bluuebunny/crossref_metadata_2025 huggingface dataset:
The growth and feeding habits of Clarias anguillaris during their first season in the floodplain pools of the Sokoto‐Rima river basin, Nigeria
Authors: Hyslop E. J.
Published: January 2006

The growth and feeding habits of juvenile Clarias anguillaris (Linné 1762) during their 5‐month residence in the floodplain pools of the Sokoto‐Rima river basin are described. A mean growth increment of 202 mm and 69.7 g attained in the October to March season compares favourably with first‐year growth recorded for other Clarias species. The diet of C. anguillaris is relatively unspecialized and includes a wide variety of items ranging from algae, higher plant material and detritus through larval dipterans, rotifers and copepods, to fish. There is variation in the diet according to month of capture and capture location, and a reduction in diet diversity with fish size. The findings are discussed in the context of work carried out on other Clarias species. It is proposed that C. anguillaris is suitable for locally operated fish culture programmes.
Serum agglutinating titres against Renibacterium salmoninarum the causative agent of bacterial kidney disease, in rainbow trout, Salmo gairdneri Richardson, and Atlantic salmon, Salmo salar L.
Authors: Bruno D. W.
Published: January 2006

Serum agglutinating titres against Renibacterium salmoninarum were determined from clinically infected, sub‐clinically infected and non‐infected rainbow trout, Salmo gairdneri Richardson, and Atlantic salmon, Salmo salar L. Titres ≥16 occurred in clinically infected rainbow trout, but declined after a few months when disease signs were absent. Non‐infected rainbow trout had titres ≤ 16. No correlation between the agglutinating titre and the level of infection was found in farmed Atlantic salmon. Variable titres were found in wild salmon broodstock although there was no evidence of BKD during 4 years of testing.
Composition and ultrastructure of elasmobranch granulocytes. I. Dogfishes (Squaliformes)
Authors: Hine P. M. , Wain J. M.
Published: January 2006

The blood granulocyte composition of 10 species of dogfish is given, together with ultrastructural observations made on Etmopterus baxteri Leydig organ and blood, and on spleens of Oxynotus bruniensis, Deania calcea, Scymnodon plunketi and blood of Centroscymnus crepidator. Neutrophilic granulocytes, which were common, had spherical granules that developed a dense core, which then lost contents to become lucent. Eosinophilic granulocytes had ovoid or elongated granules with a fibrillar content that became aligned longitudinally, and rarely formed an axial rod. Eosinophils had large spherical granules that were electron‐dense but in early stages had a disorganised fibrillar content. These cells correspond to the neutrophils, heterophils and eosinophils, respectively, of other elasmobranchs.

Dogfish granulocytes are compared with those of other elasmobranchs, and their lack of similarity to those of higher vertebrates is noted.
Composition and ultrastructure of elasmobranch granulocytes. III. Sharks (Lamniformes)
Authors: Hine P. M. , Wain J. M.
Published: January 2006

The peripheral blood granulocyte composition of five species of shark is given together with ultrastructural observations made on the epigonal organ and blood of Mustelus lenticulatus and spleen of Apristurus sp. Three granulocyte lineages occurred in Mustelus. Ultrastructurally, eosinophilic granulocytes contained granules that were very variable in size and contained parallel fibrillar arrays that were unidirectional in small granules, but which were often orientated in several directions in larger granules. This dense core material sometimes formed angular crystalloids.

Eosinophils had ovoid or irregular granules that were usually uniformly electron‐dense, but some had an eccentric ovoid area of greater electron‐density. Some eosinophils enter the blood where they are phagocytic, but others, in blood and epigonal organ, showed an unusual but characteristic process of disintegration, leaving a ragged cell full of cellular debris.

The third granulocyte type had features of mast cells and basophils of higher vertebrates and was tentatively identified as belonging to that lineage. The inter‐relationships of these cells, and of them with granulocytes of other elasmobranchs, are discussed.
Sex‐inversion of the hermaphroditic, protogynous teleost Coris julis L. (Labridae)
Authors: Brusléa S.
Published: January 2006

Sex‐inversion of Coris julis, a protogynous hermaphrodite, was studied using histological and cytological criteria. Four stages were recognized: oocyte and oogonial atresia; occurrence of spermatogonia with primordial germ cells (PGC) in the ovarian wall; onset of spermatogonial proliferation; considerable proliferation of spermatogonia and PGC with build‐up of seminiferous tubules. Spermatogonia arise from PGC, undifferentiated and bipotential cells, in which mitotic activity was detected.
Blood pressure, electrolyte composition and renal studies of pike, Esox lucius, following administration of salmon calcitonin
Authors: Wales N. A. M. , Gaunt T.
Published: January 2006

Pike were adapted to both fresh water and brackish water (salinity 2.2‰) conditions prior to measurements of blood pressure, electrolyte composition and renal function both before and after administration of either 3.75 μg calcitonin kg−1 body weight or acetate saline. This protocol was designed to test the ability of calcitonin to affect significantly the fluid and electrolyte status of fish exposed to varying salinity. Whilst in freshwater‐adapted animals the plasma content of calcium and magnesium was significantly depressed following calcitonin injection, no corresponding effect was seen following 2.2‰ salinity brackish water‐adaptation. Moreover, no significant changes were apparent in renal function of pike adapted to either medium. It is concluded from these experiments that calcitonin in pike may play some part in extra‐renal control of plasma calcium and magnesium content in fresh water but that it is unable to affect significantly the measured plasma ion content of brackish water‐adapted animals.
Kinetics of transfer of immunity by immune leucocytes and PFC response to HRBC in isogeneic ginbuna crucian carp
Authors: Nakanishi T.
Published: January 2006

Transfer of immunity to horse erythrocytes (HRBC) by immune lymphoid cells was performed to analyze the kinetics of adoptive immunity in the clonal ginbuna crucian carp, Carassius auratus langsdorfti. Immune lymphoid cells were intravascularly transferred to the unprimed recipients and then recipients were evaluated by measuring the antibody titre of the plasma. Antibody productivity was most successfully conferred by splenic cells, followed by pronephric and mesonephric cells, taken from immune donors 7 days post‐immunization, while transferability by thymic cells was lacking or very low, even if possible. Peak response of plaque‐forming cells (PFCs) was observed at 5–7 days after the first injection, and the maximum number of PFCs at peak response was almost the same in all organs examined, such as the pronephros, mesonephros, spleen and the thymus. Direct correlation between transferability and number of PFCs was not observed on individuals, although the peak of transferability corresponded to that of the PFC response. Preliminary experiments of cell transfer by separated pronephric cells showed that the lymphocyte‐rich fraction was more effective than the bottom fraction containing fewer lymphocytes in transferring immune reactivity. These results suggest that cells involved in transferring immune reactivity are B lymphocytes, composed of different developmental stages and distributed differently in the different lymphoid organs.
Individual growth and smoltification of juvenile masu salmon, Oncorhynchus masou Brevoort, under rearing conditions
Authors: Hirata T. , Goto A. , Yamazaki F.
Published: January 2006

In a reared population of individually marked juvenile masu salmon, individual growth was monitored from the first autumn in 1983 to the following spring. The potential smolts were not significantly greater in mean fork length and body weight than the potential parr in late August of the first year, but they then grew faster until March of the second year. As a result, the potential smolts formed the upper mode of the bimodal length distribution after February. Especially in autumn (October and November) the specific growth rates of potential smolts were significantly greater than those of parr, and the bimodality in growth rate distribution was more distinct for males than females. These suggest that there are two groups having different growth rates in autumn of the first year and that sufficient growth in this period may play an important role in smoltification in the following spring.
Identification of grey mullet (Teleostei: Mugilidae) juveniles from British waters
Authors: Reay P. J. , Cornell V.
Published: January 2006

Examination of juveniles (25–50 mm t.l.) of the three species of grey mullet present in British and other nothern European waters has indicated that the melanophore pattern on the ventral surface of the head is a reliable and useful character for identification.
The role of air breathing in the resistance of bimodally respiring fish to waterborne toxins
Authors: Kulakkattolickal A. T. , Kramer D. L.
Published: January 2006

The bimodally respiring catfish Clarias macrocephalus Günther responded to a toxic extract of Croton tiglium (Euphorbiaceae) seeds by increased air breathing under both normoxic (8.1 ± 0.4 mgO2 l−1) and hypoxic (0.7 ± 0.1 mgO2l−1) conditions. Fish in hypoxia survived longer than those in normoxia when surface access was provided. When air breathing was prevented, survival time in toxin was greatly reduced at both levels of dissolved oxygen, and fish in normoxia survived longer than those in hypoxia. Non‐toxin controls without surface access survived in normoxia but in hypoxia died at the same time as the fish in toxin. These results suggest that air breathing increases the resistance offish to toxins by permitting a decrease in the rate of gill ventilation and hence the rate at which toxins are absorbed.
Presumptive mycobacteriosis in North‐east Atlantic mackerel, Scomber scombrus L.
Authors: MacKenzie K.
Published: January 2006

A total of 9470 mackerel aged from 0 to 20 years was examined for a disease condition whose causative agent has not been identified but which resembles mycobacteriosis. The study area extended from off Portugal to the northern North Sea. Most mackerel over 2 years old snowed evidence of gross infection. Mean intensity increased with age, indicating a chronic disease of low pathogenicity. There is statistical evidence of an adverse effect on growth, and it is suggested that this may delay first spawning of some young mackerel for at least 1 year. Western stock mackerel appear to be more heavily infected than North Sea stock, and the lowest levels of infection were found off Portugal. The general level of infection decreased in the most recent year classes examined–those of 1982, 1983 and 1984.
Widespread hybridization between native Atlantic salmon, Salmo salar, and introduced brown trout, S. trutta, in eastern Newfoundland
Authors: Verspoor E.
Published: January 2006

Hybridization between native Atlantic salmon and introduced brown trout was found to occur at a mean frequency of 0.9% in Atlantic salmon populations in eastern Newfoundland. Hybrids were detected in five of the 10 watersheds studied, but consideration of sampling error suggests that they could have been present in the remaining five watersheds although they were not detected. The frequency found in the Newfoundland and other North American salmon populations is significantly greater than the 0.3% reported for salmon populations in the British Isles, and both are higher than frequencies observed in salmon populations in Sweden. The higher frequency in North America is in accord with the prediction that hybridization between species will be more frequent where one species is introduced than in areas where both are native.
Burst swimming speeds of mackerel, Scomber scombrus L.
Authors: Wardle C. S. , He P.
Published: January 2006

Burst swimming speeds were measured in mackerel 0.275–0.380 m long by filming newly caught fish, first released into a large shore‐sited tank, using a high‐speed cine camera and real time TV camera. The highest speed was 5.50 m s−1 or 18 body length per second (b.l. s−1) in a 0.305 m long mackerel at 12° C. The recorded maximum tail beat frequency of 18 Hz agrees well with 19 Hz predicted from the measured contraction time of 0.026 s for the anterior lateral swimming muscle. The stride length was close to 1 B.L.; the power, calculated from the drag, was 4.53 W, and, calculated from the muscle used, was 5.07 W; all suggesting that the mackerel is swimming close to its physiological limit.
A preliminary assessment of the biomass of the pelagic sardine Limnothrissa miodon in Lake Kariba
Authors: Marshall B. E.
Published: January 2006

The sardine Limnothrissa miodon was very patchily distributed in Lake Kariba in 1981–1983 and its mean biomass was 59 23 kg ha−1, declining from 90–91 kg ha−1 in 1981 to 38–66 kg ha−1 in 1983. In addition, the mean size of the fish fell from 55–2 mm in 1981 to 49–9 mm in 1983. These changes are attributed to the effects of drought and reduced river flows as well as to the high level of commercial fishing for this species. There was a correlation between commercial catches and biomass estimates which allowed estimation of biomass in previous years from fishing statistics. Fishing effort appeared to be a major influence on sardine abundance: total biomass in 1985 was about 10% of what it was in 1974 when the fishery began. When expressed in terms of unit area, as is usual for African lakes, the pelagic biomass appeared to be greater in Lake Tanganyika, where Limnothrissa is endemic, than in Lake Kariba, although there is little difference in their primary productivity, but consideration in terms of volume rather than area shows that this was not the
The effect of β‐adrenergic blockade on the recovery process after strenuous exercise in the rainbow trout, Salmo gairdneri Richardson
Authors: van Dijk P. L. M. , Wood C. M.
Published: January 2006

Trout fitted with arterial catheters were subjected to 6 min of strenuous exercise, injected with either saline (controls) or the β‐adrenergic antagonist propranolol, and monitored over the following 8‐h recovery period. Control responses were very similar to those previously reported, except for much higher resting and post‐exercise plasma catecholamine levels, and less marked RBC pHi regulation, perhaps due to season (February–May). Trout subjected to prior β‐blockade would not exercise. Trout β‐blocked immediately after exercise showed a much higher incidence of mortality during the recovery period, but accompanying symptoms were similar to those previously documented in control trout dying after exercise. Specific effects of post‐exercise β‐blockade seen in both survivors and mortalities were a sustained elevation of arterial Pco2 and an inhibition of blood glucose elevation. There were negligible effects on RBC pHi and volume regulation, blood metabolic acid and lactate dynamics, or plasma ion changes. The results provide little support for the hypothesis that β‐adrenergic actions of plasma catecholamines are intimately involved in post‐exercise recovery, but must be considered in the context of the ‘winter’ trout, where β‐responses may be diminished.
A natural hybrid of Leuciscus cephalus macedonicus X Chalcalburnus chalcoides macedonicus (Pisces, Cyprinidae) from Lake Volvi (Macedonia, Greece)
Authors: Economidis P. S. , Sinis A. I.
Published: January 2006

A massive hybridization between Leuciscus cephalus macedonicus and Chalcalburnus chalcoides macedonicus has been recognized and studied by examining 67 specimens from Lake Volvi (Macedonia, Greece). The majority of meristic and other characters present an intermediate position in the hybrid (total hybrid index Vh= 38.37). Nevertheless, the best expression of intermediacy is shown most clearly by the numbers of anal fin soft rays, lateral line scales and gill rakers, and also by the height of the dorsal fin and the length of the base of anal fin. Of the examined hybrid specimens. 92.5% were females. It seems that hybridization takes place during the reproduction period in the main streams flowing into the lake under special conditions which hinder the migration of the majority of the population of C. chalcoides from the lake to the breeding sites. It is suggested that individuals of C. chalcoides, which manage to arrive in these sites, mate with L. cephalus, the normal inhabitant of the streams, thus producing the hybrid.
The fish community of an East African mangrove creek
Authors: Little M. C. , Reay P. J. , Grove S. J.
Published: January 2006

The results of a beach seine survey of an East African mangrove creek are presented. The fish community of the creek is described and is compared with that of a nearby lagoonal site and with those described for other mangrove and estuarine systems. The species composition was found to differ substantially between the creek and the lagoon site, though diversity indices for the two areas were similar. Eighty‐three species of teleost fish werecollected from the mangrove area of the creek. This number is considered high in relation to comparable studies and is attributed to the constant high salinity (approximately 35%o) measured throughout the study period. Approximately 90% of the fish caught were juveniles. Plankton sampling was also carried out and representatives of 21 fish families were collected as larvae within the creek. Catches from both beach seining and plankton sampling in the mangrove areas were dominated numerically by resident clupeid and gobiid species. The majority of species, however, were considered to have a widespread distribution as adults. A discrepancy between the catch composition of larvae and juveniles suggests that species that use the creek as a nursery area enter the system principally at a post‐larval/ juvenile stage of development. No systematic spatial or temporal variation in the community structure was identified over the study period.
Feeding motivation and response to predation risk in Atlantic salmon parr adopting different life history strategies
Authors: Huntingford F. A. , Metcalfe N. B. , Thorpe J. E.
Published: January 2006

Feeding intensity was measured before (baseline level) and after (disturbed level) brief exposure to a potential predator in groups of 0+ Atlantic salmon, Salmo salar. parr destined to follow either a fast‐growth, early‐smolting life history (upper modal group or UMG fish) or a slow‐growth, late‐smolting life history (lower modal group or LMG fish). Feeding intensity decreased following exposure to the predator. While the absolute decrease in feeding intensity is constant regardless of baseline level, the proportionate decrease is negatively related to pre‐presentation feeding intensity. Parr that are strongly motivated to feed thus maintain a higher food intake and incur greater risks when foraging in the presence of a predator. No differences in baseline or disturbed feeding intensity of UMG and LMG parr were found up to September of their first year. Previous work has shown that baseline feeding intensities decrease in LMG fish after September but increase in UMG fish. In the present study, these differences were reflected in greater disturbed feeding intensities in UMG fish, but fish destined to follow different life history patterns do not differ in risk‐taking, once these differences in baseline feeding motivation have been taken into account.
The effects of reversal of seasonal changes in photoperiod on the growth and food consumption of cod, Gadus morhua L.
Authors: Hall S. J.
Published: January 2006

The effect of reversing the natural seasonal change in photoperiod on the feeding and growth of juvenile cod, Gadus morhua. was investigated in two experiments. In an experiment conducted in spring no photoperiod effects on overall growth and food consumption were observed; however, tissue analysis at the end of the experiment showed that treatment groups differed significantly in their muscle water content. A repeat experiment conducted in early winter similarly failed to reveal an effect of photoperiod reversal on overall growth and feeding, although a very marked decline in growth rate was observed for all fish. The decline in growth rate observed in the second experiment cannot be accounted for by any changes in experimental procedure and is interpreted as possible evidence for an endogenous circa‐annual rhythm in growth rate.
A comparison of the composition of the juvenile fish catch from the Sokoto–Rima floodplain, Nigeria in years preceding and immediately after upstream dam completion
Authors: Hyslop E. J.
Published: January 2006

The species composition of the juvenile fish catch from part of the Sokoto–Rima floodplain was monitored over four seasons. In three of the years, 1981–1984, the flood pattern of the river was normal. During the 1984–1985 season the cycle was disrupted by completion of the Goronyo Dam, approximately 100 km upstream from the sampling area. The composition of the juvenile fish catch was markedly altered during this season and the diversity greatly reduced. Ways in which fish species could be affected by the change in flood regime are discussed.
The effect of feeding frequency on utilization of algal nutrients by the marine herbivore, the luderick, Girella tricuspidata (Quoy and Gaimard)
Authors: Anderson T. A.
Published: January 2006

Utilization of whole algae, lipid, protein and total nitrogen and total carbon by the luderick, Girella tricuspidata, fed ad libitum were found to be comparable with published results obtained for other species. Periods of food deprivation were found to cause reduced efficiency of utilization for all nutrients measured, with a 4–day deprivation period having a greater effect than a 24–h deprivation period.

Only animals fed ad libitum were able to obtain a greater amount of lipid from their food than was defaecated. Utilization of protein and non–protein nitrogen is similar in fish fed ad libitum, but a greater reliance upon the non–protein nitrogen content of the food for nutrition is apparent when the fish are subjected to periods of food deprivation. Nitrogen utilization, relative to other nutrients, by fish subjected to periods of food deprivation is greatest immediately after a feeding bout. Total carbon utilization relative to other nutrients increases with increasing time of deprivation following a feeding bout.

It is suggested that these changes in nutrient utilization with time after feeding are the result of rapid utilization of the nitrogen–rich cell contents, followed later by utilization of the algal cell wall.
Influence of photoperiod on growth changes in juvenile Atlantic salmon, Salmo salar L.
Authors: Villarreal C. A. , Thorp J. E. , Miles M. S.
Published: January 2006

During their first 6 months sibling Atlantic salmon parr, Salmo salar L., grew larger under constant light than under natural photoperiod or simulated natural photoperiod (control). When rate of change of photoperiod was accelerated after midsummer, ×2, ×3 and ×4, there were no growth differences between the three groups, but all were smaller than the control population. Under constant autumn photoperiod of 8 h light: 16 h dark growth was less than under all other experimental photoperiod conditions. Mean length was directly correlated with total hours of daylight experienced, excluding those fish kept under constant light.

Fish reared from first feeding under photoperiod regimes delayed 6 and 9 months out of phase with the natural light cycle were smaller than the controls, whereas those under a regime 3 months out of phase did not differ from the controls. The clear segregation of modal length groups within the 3, 6 and 9 months out‐of‐phase populations occurred 1, 4 and 4 months, respectively, after the segregation in the control group. Under constant light, and under constant 12 h light: 12 h dark (12 LD), the segregation was delayed 3 and 4 months, respectively. The proportion of the population which maintained growth (upper modal group) was significantly less in the 9 and 6 months out‐of‐phase and 12 LD groups (39, 40 and 42%, respectively) than in the other three groups (82.5‐85%). Acceleration of photoperiod change also resulted in decreased growth.

The results support a model of salmon development in which, 2‐3 months after first feeding, growth is maintained if feeding opportunities at that time are above a threshold level, and in which this critical timing is influenced by photoperiod. It is suggested that the delays reflect a synchronizing effect of photoperiod on an endogenous rhythm of appetite and growth. The differences in upper modal group proportions observed in the present experiments, reflect the relative feeding opportunities available at the critical period in July‐August.
The influence of alarm substance and shoal size on the behaviour of zebra danios, Brachydanio rerio (Cyprinidae)
Authors: Rehnberg B. G. , Smith R. J. F.
Published: January 2006

Timidity, vigilance and response to alarm substance were examined in shoals consisting of one to 12 zebra danios, Brachydanio rerio. Measures of timidity were not clearly related to shoal size. Fish in larger shoals spent more time in central areas of the tank away from cover than fish in smaller shoals. However, fish in small shoals appeared to be as aggressive as those in larger shoals. Vigilance and foraging rates did not appear to be related to shoal size. Per capita foraging rates and shoal size were not correlated. After being frightened by alarm substance, danios in larger shoals did not return to foraging sooner than those in smaller groups. Zebra danios in all shoal sizes responded behaviourally to alarm substance. It appears that the presence of conspecifics is unnecessary for alarm behaviours to occur and that the nature of the behaviours are independent of shoal size.
Effect of individual and group rearing on age and size at maturity of male mosquitofish, Gambusia affinis
Authors: Campton D. E. , Gall G. A. E.
Published: January 2006

Age and size at sexual maturity were significantly greater for male mosquitofish, Gambusia affinis Baird and Girard, reared in sib‐groups than for their sibs reared individually. Age at sexual maturity averaged 43.3 and 62.1 days for individually‐ and group‐reared males, respectively, a 43% difference; final length and weight at maturity were 7.7 and 34.2% greater, respectively, for group‐reared males than for their individually‐reared sibs. The results were consistent among 30 families that represented the progeny of 30 wild‐caught females. The observed differences may be attributable to behavioural interactions affecting the neuroendocrine control of the maturation process, as suggested by previous studies of Xiphophorus.
Ontogenetic changes in the diet of early post‐settlement Scarus species (Pisces: Scaridae)
Authors: Bellwood D. R.
Published: January 2006

Ontogenetic changes in the diet of early post‐settlement Scarus species are described, based on analyses of intestinal contents. There is a marked change‐over from carnivory to herbivory. Newly settled individuals feed on Crustacea, primarily harpacticoid nauplii and adults, whilst larger juveniles almost exclusively ingest algae and sand. In comparison, the diets of recentlysettled Acanthuridae, Siganidae and Pomacanthidae were found to be almost exclusively herbivorous.
Effects of sampling conditions on selected blood variables of rainbow trout, Salmo gairdneri Richardson
Authors: Korcock D. E. , Houston A. H. , Gray J. D.
Published: January 2006

The effects of two methods of specimen immobilization (MS 222 anaesthesia and stunning), two types of anticoagulant (EDTA and heparin), two storage temperature ranges (0–2°C and 22–25°C) and four sample storage periods (0, 1, 3, and 24 h) on the haemoglobin, haematocrit, plasma and packed cell sodium, potassium and chloride ion concentrations and packed cell ATP levels of rainbow trout were examined. Stored samples exhibited increases in cell volume, net transfer of sodium and chloride from plasma into cells, net loss of potassium to plasma and rapid depletion of ATP. Room temperature conditions and prolonged storage exacerbated these changes. Use of EDTA, particularly in combination with MS 222, frequently led to haemolysis. Least change in most variables was observed in samples drawn from stunned specimens, treated with heparin and refrigerated before use or preparation for deep cold storage.
Age, growth and reproduction of the barbel, Barbus sclateri (Günther, 1868), in a first‐order stream in southern Spain
Authors: Herrera M. , Hernando J. A. , Fernandez‐Delgado C. , Bellido M.
Published: January 2006

This study was based on examination of 1476 barbels from a first‐order stream located in the Guadalquivir River basin (38°N, 4°43′W). This stock comprised nine age groups of male and 11 of females. No growth was recorded between October and March, most occurring in April–June and, to a lesser extent, in July–September. A classification analysis revealed that this stock had the lowest growth rate of 37 different European barbel populations. Length–weight relationships were obtained for 12 barbel categories and used to estimate both condition and instantaneous growth rate. Relative condition (before and after subtracting gonad weight) was similar in both sexes and was affected by gonad growth and environmental summer conditions.

Spawning occurred during the second half of May (15 May is suggested as the birthday). Gonads began to develop in September (females) and in February (males). Males matured at between 7 and 9 cm fork length (f.l.) (2–4 years old) and females between 11 and 16 cm (6–7 years). The fecundity of this stock was represented by the formula F=6.07 10 4 f.l. (mm)3.0667. Larger and older fish showed a higher fecundity and bigger eggs. The overall sex ratio did not differ from 1:1.
Bioenergetics of growth of a cyprinid, Phoxinus phoxinus: the effect of ration, temperature and body size on food consumption, faecal production and nitrogenous excretion
Authors: Cui Y. , Wootton R. J.
Published: January 2006

Food consumption, faecal production and nitrogen excretion by minnows, Phoxinus phoxinus, weighing 1–5.5 g were studied at five rations ranging from starvation to ad libitum and four temperatures ranging from 5 to 15°C.

The maximum rate of food consumption (Cmax) was related to body weight (W) and temperature (T) by the relationship: Cmax=aWb1Tb2. There were significant daily variations in Cmax, which tended to decline over time. Absorption efficiency increased with increasing ration size and decreasing temperature. Body weight had no significant effect on the faecal production. The equation F= aCb1eb2 T described the relationship between faecal production (F), food consumption (C) and temperature. Ammonia‐N predominated over urea‐N in the excreta of most experimental fish. The proportion of urea‐N in the total nitrogen excreted was generally higher at lower rations than at higher rations. Rates of nitrogen excretion increased with increased ration size and were, to a lesser extent, influenced by temperature. Body weight had no significant effect on the nitrogen excretion by feeding minnows. The equation N = a+blT+b2C described the effects of food consumption and temperature on nitrogen excretion (N) other than urea‐N excretion. The relationship between urea‐N excretion (Nu), food consumption and temperature was described by the equation Nu= aeb1T((C+1)b2.

On the average, 11 % of food energy was lost in faecal production and nitrogen excretion by minnows feeding on whiteworms, Enchytraeus spp.
Length‐dependent changes in egg size and fecundity in females, and brooded embryo size in males, of fork‐tailed catfishes (Pisces: Ariidae) from the Sepik River, Papua New Guinea, with some implications for stock assessments
Authors: Coates D.
Published: January 2006

Data suggest that mature egg weight is positively correlated to female parent length in all five species of fork‐tailed catfish studied. Embryo weight is positively correlated with the length of the male mouthbrooding parent in the four species where data are available. Non‐random mate pairing is probably between fish of equivalent size. Fecundity appears to be linearly related to female fish length in all species. There is no significant correlation between fecundity and female weight, probably because egg size increases with fish size. Low fecundities and breeding behaviour suggest that recruitment is likely to be highly density‐dependent and the stocks vulnerable to increased mortality (fishing). Changes in egg size with fish size may account for deviations from a cube relationship between fecundity and fish length in other species. The relevance of this to other fish stock assessments is discussed. Attention is drawn to possible changes in egg size with fish length which could affect recruitment in fished stocks, depending on the specific relationship and the length at which mature fish are caught.
Age and growth parameters of Siganus sutor in Kenyan marine inshore water, derived from numbers of otolith microbands and fish lengths
Authors: Ntiba M. J. , Jaccarini V.
Published: January 2006

Siganus sutor (Valenciennes, 1835) is, together with the Lethrinidae, commercially the most important fish of Kenyan waters. Age and growth parameters of this fish have been estimated for stock assessment purposes, using the von Bertalanffy growth model while taking into account the initial small but finite length of fish, Lo. Microbands on the otoliths were used as a measure of age in days. Data of fish length against numbers of microbands were fitted to the growth formula by a least squares procedure applied to a non‐linear fit. This gave an L∞ of 36.2 cm s.l. and a K of 0.87 on an annual basis. Independently, a curve was fitted by eye to the same data, and values were read off the curve and used in a standard Ford–Walford plot. This gave an Lx of 35 cm and a K of 0.9. The close agreement of the values obtained by the two methods, and of these with values in the literature, demonstrates the value of using microbands for determining growth parameters in a tropical fish.
Differential effects of largemouth and smallmouth bass on habitat use by stoneroller minnows in stream pools
Authors: Harvey B. C. , Cashner R. C. , Matthews W. J.
Published: January 2006

Previous investigations of within‐reach distribution patterns of the stoneroller minnow, Campostoma anomalum Rafinesque, suggest that this species behavioural response to piscivorous bass differs among streams with different bass species. This study compares the responses of Camposloma to two common piscivorous fishes, largemouth bass, Micropterus salmoides Lacepede, and smallmouth bass, M. dolomieui Lacepede. Field experiments in Brier Creek, Oklahoma, U.S.A. showed that Campostoma responded to the presence of adult largemouth bass by shifting to shallow water habitats (commonly < 20 cm), but responded weakly or not at all to adult smallmouth bass. The magnitude of the response of Campostoma was positively related to activity level of the predators. Differences in behaviour between these two predator species may contribute to the differences in spatial distribution patterns of Micropterus and Campostoma observed in earlier investigations, but differences in stream channel morphology and temperature regimes among streams may also be important.
Kinetic analysis of the swimming behaviour of bluegill sunfish, Lepomis macrochirus Rafinesque, exposed to copper: hypoactivity induced by sublethal concentrations
Authors: Ellgaard E. G. , Guillot J. L.
Published: January 2006

The concentration of copper which caused 50% mortality of bluegill in 96 h (96‐h LC50) was between 4 and 16 ppm of the metal, copper. During the 6–8 day treatment period, sublethal concentrations of copper elicited a hypoactive locomotor response which was dependent on both concentration and time of exposure. Fish treated in 0.04, 0.08 and 0.4 ppm of copper were only 67, 61 and 44% as active, respectively, as they were prior to treatment. Locomotor activity decreased dramatically during the first 4 days of exposure to copper and remained low during further exposure.
Diet, gastric evacuation rates and food consumption in a stunted population of Arctic charr, Salvelinus alpinus L., in Takvatn, northern Norway
Authors: Amundsen P. A. , Klemetsen A.
Published: January 2006

Diet and food consumption of a stunted population of Arctic charr in Takvatn, northern Norway, was studied throughout the ice‐free season. Chironomid pupae dominated the diet in June, July and August, while zooplankton and three‐spined sticklebacks dominated in September and October. Estimates of gastric evacuation rates were obtained from laboratory experiments with wild‐caught, acclimated charr, and these estimates were used for in situ estimation of food consumption from weights of stomach contents. The daily food consumption was greatest in July, after which it decreased markedly towards autumn. The estimated food intake rates were low, especially in September and October. The food supply appears to be restricted, which is probably the main reason why the charr in Takvaln exhibit stunted growth.
Diel movements of scalloped hammerhead sharks, Sphyrna lewini Griffith and Smith, to and from a seamount in the Gulf of California
Authors: Klimley A. P. , Butler S. B. , Nelson D. R. , Stull A. T.
Published: January 2006

Occurrences of 18 scalloped hammerhead sharks tagged with coded ultrasonic transmitters were recorded at seamount El Bajo Espiritu Santo in the Gulf of California over a 10‐day period by automated, data‐logging monitors. These sharks remained grouped at the seamount during the day and moved separately into the surrounding pelagic environment at night. The temporal pattern of shark occurrences was related to the light‐dark cycle: individuals departed prior to dusk and returned near dawn next morning. However, arrivals and departures of more than one shark within short daytime periods indicated group movements to and from the seamount. Sharks returned repeatedly to the tagging site and not to another site centred less than 240 m from the former site.
An electrophoretic and biometric study of Arctic charr, Salvelinm alpinus (L.), from ten British lakes
Authors: Partington J. D. , Mills C. A.
Published: January 2006

Samples of Arctic charr, Salvelinus alpinus (L.), were collected from the eight Cumbrian lakes containing all the known English populations. Comparative material was obtained from North Wales and southern Scotland. Comparisons were performed using otolith ages, meristic and morphological characters and by assessing allele frequencies for serum esterase and for skeletal muscle malate dehydrogenase. The results confirm that both basins of Windermere contain spring and autumn spawning races of charr. As well as differing genetically and exhibiting differing growth rates, the two races have different mean gill raker numbers and mean gill raker lengths. The latter two variables were used to derive a discriminant function which enables individual charr to be ascribed to the correct race with 94‐96% accuracy. Within both principal races there were further significant differences between charr from the north and south basins of the lake and possibly also between different spawning grounds within each basin. Variation between six of the remaining seven Cumbrian populations is significant but generally no greater than that between the Windermere spring and autumn spawners. The exception is the Ennerdale charr which stands out on morphological, meristic and genetic characters, has a rapid growth rate despite its oligotrophic environment, and is a river rather than a lake spawner. The charr from North Wales and southern Scotland were clearly distinct, both from each other and from the English populations.
Choice of feeding station in Atlantic salmon, Salmo salar, parr: effects of predation risk, season and life history strategy
Authors: Huntingford F. A. , Metcalfe N. B. , Thorpe J. E.
Published: January 2006

The current speed at which underyearling salmon parr held feeding stations was examined from late summer to early winter in laboratory flume tanks that offered a choice between (a) areas with high water flow, high food availability but high predation risk and (b) areas with low flow, little food but shelter from predators. In August, those fish that would become smolts aged 1 + (and which by late winter formed the upper modal group, UMG, of the bimodal size distribution) adopted positions in faster currents than did the fish which would take a further year to reach the smolt stage (the lower modal group, LMG). However, the chosen current speed of UMG fish decreased through the period of study, so that by December all fish were found in areas of low flow, and hence little food. Both date and water temperature had independent effects on the chosen current speed of UMG fish.

The effect of predation risk was investigated using a model trout. A brief sight of this predator caused 47% of fish that had been in the main, exposed currents to move to slacker, sheltered areas; they took 1 h, on average, to return to their previous position. The fish that remained in position upon seeing the predator reduced their rate of tail beating, presumably increasing crypticity. Eventual UMG parr were less likely than were LMG fish to move away upon seeing a predator. The fish moved to faster currents than normal 2–3 h after seeing the predator, possibly compensating for the earlier reduction in feeding rate.
The seasonal partitioning of energy in an estuarine fish, the common goby, Pomatoschistus microps Krøyer
Authors: Rogers S. I.
Published: January 2006

The common goby, Pomatoschistus microps, is an abundant brackish water species which has an appreciable role, both as predator and prey, in the ecosystems of British estuaries. The partitioning of energy within each sex is described and discussed, and energy values are provided for the gonad, liver and carcass throughout almost the entire life of one year class. Partitioning of resources within the body at different times of the year shows considerable variation, not only with time but also between the sexes. In particular, the energy content of the male gonad during the spawning season is never more than 3.7% of that of the female. Important aspects of the biology of the species which relate to energy partitioning are maturation at an early age, high reproductive investment, high stochastic mortality, and death usually after a single breeding season.
Beam trawl surveys as a monitoring tool in polluted estuaries in north‐east England
Authors: Pomfret J. R. , Turner G. S. , Phillips S.
Published: January 2006

Surveys of demersal fish and epibenthos in the Tyne, Wear and Tees estuaries, begun in 1981 as part of a wider sampling programme to assess the effects of pollution and its reduction by various control measures, are discussed. Available survey methods are reviewed and the development of a survey protocol is described. A preliminary assessment of the data identified differences between the estuaries and the distribution of major species in the Tyne, and provides evidence of long‐term water quality improvements.
A model to predict the level of artificial radionuclides in environmental materials in the Severn Estuary and the Bristol Channel
Authors: McColl N. P.
Published: January 2006

The SEVERN compartment model, of the Bristol Channel and Severn Estuary, has been developed for use in predicting environmental concentrations of artificial radionuclides present in the estuary. A comparison between predicted and measured values of salinity and environmental 137Cs concentrations has demonstrated the overall validity of the model. SEVERN has been used to assess the radiological impact of radionuclides present in the estuary which result from low‐level routine discharges from the nuclear power industry.
Movements of Atlantic salmon, Salmo salar L., in an estuary in south‐west England
Authors: Potter E. C. E.
Published: January 2006

In the years 1985–1987, salmon were tracked in the estuary of the River Fowey, Cornwall using the ‘sonar buoy’ system developed at the M.A.F.F. Fisheries laboratory and described by Solomon & Potter (1988). Sixty‐one salmon were caught and tagged in the estuary, 25 with radio and 36 with combined radio and acoustic transmitters. About half these fish were not recorded entering the freshwater reaches of the R. Fowey, and from tag recoveries it seems likely that about 27% were returning to other rivers. For fish returning to the R. Fowey the time between tagging and entry into fresh water varied between 9 h and 130 days. In the estuary the fish largely moved in the same direction as the tidal currents, although movements over the ground against the current were more common in the bottom 2 km and the top 2 km. During periods of low river‐flow in summer all salmon tracked in the estuary dropped back out to sea where they stayed for varying periods: some of these made several sorties past the estuary mouth and on occasions well up the estuary before finally entering fresh water. During periods of higher river discharge, in both the summer and the autumn, some fish remained in the estuary for longer periods, sometimes holding position in deep, sheltered water. Most fish entered fresh water at night during periods of increased freshwater discharge, although at very high flows fish also entered in daylight.
Ria de Alvor as a spawning place and a nursery ground
Authors: Antunes M. M. , da Cunha P. L. , Duarte A. P. , Mendonça E. P.
Published: January 2006

Ria de Alvor is a small estuary between Lagos and Portimão on the south coast of Portugal, 37°7′–37°10′N, 8°35′–8°38′W.

Samples were collected monthly in the period April 1985–March 1986 in an ichthyoplankton and ichthyofauna survey of the estuary. A WP‐2 plankton net was used for catching ichthyoplankton, and a beam trawl and a beach seine were used for catching ichthyofauna.

Scaldfish, Arnoglossus laterna (Walbaum, 1792), even though the most abundant species in ichthyoplankton samples, was never found in ichthyofauna samples.

From the results obtained, it is concluded that a great part of the fish species are temporary marine visitors using the Ria as a nursery ground, although this system appears to provide a spawning area for species with benthic eggs. No evidence was found of pelagic spawning.
Plaice nurseries: effects on recruitment
Authors: Bergman M. J. N. , van der Veer H. W. , Zulstra J. J.
Published: January 2006

The function of coastal nursery areas is discussed in relation to the variability in North Sea plaice recruitment. Since 60% of the recruitment of juveniles originates from the Wadden Sea, special attention is paid to this area. The concentration of juveniles in a restricted area seems to evoke only adverse effects: an increased risk of food limitation and hence reduced growth, and an increased vulnerability to predation. Despite these expectations, growth of most of the plaice in the Wadden Sea has always been optimal within the wide range of year‐class strength observed and depends only on ambient water temperature. The same situation is indicated for some British bays, where the growth of 0‐group plaice is far lower than in the Wadden Sea, because of lower temperatures. Mortality through predation seems to be relatively low in the Wadden Sea and restricted to only a short period, because of the absence of almost all potential predators. In the more open British bays higher mortalities are found, probably due to the presence of a number of predatory fish species. The low variability in the recruitment of plaice might be the combined result of optimal growth with the absence of between‐year fluctuations in predator abundance in the Wadden Sea. As a result, observed mortality only depends on prey abundance and is therefore density‐dependent both within one year and especially between years, reducing variations in recruitment. This suggestion is supported by the situation in more open British bays: here too, growth is maximal, but the abundance of predators shows larger fluctuations between years and, as a result, greater fluctuations in mortality are observed.