bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolutionary relationships of Gadopsis spp. inferred from restriction enzyme analysis of their mitochondrial DNA
Authors: Ovenden J. R. , White R. W. G. , Sanger A. C.
Published: January 2006

Gadopsis marmoratus and G. bispinosus are the sole members of an endemic Australian genus of percoid fishes. At least nine mitochondrial genotypes, identified by site polymorphisms for seven restriction enzymes, were found among 50 individuals from the two species sampled during this study. Net divergence between G. marmoratus and G. bispinosus was 6.60%, or at least 12.65 mutations. Mean divergence within G. marmoratus was 5.98%, or at least 12.29 mutations. The southern and northern forms of G. marmoratus are monophyletic taxa and the amount of divergence between the two forms confirms that a detailed taxonomic study is necessary to review the status of G. marmoratus. Despite detailed phytogenies constructed from restriction enzyme analysis of mitochondrial DNA, the relationship between G. bispinosus and the northern and southern forms of G. marmoratus was not resolved.
Fish community structure in lowland drainage channels
Authors: Townsend C. R. , Peirson G.
Published: January 2006

Land drainage channels constitute a vast network of aquatic habitat utilized by fish. Surveys of these channels (dykes) in Broadland in eastern England reveal similar fish communities whether the dykes drain grazing marsh, fenland or arable land, though there are indications of poor recruitment in the recently deeply drained dykes of arable land. The species encountered most predictably were pike, roach, eel and tench. In terms of biomass, pike ranked top, followed by tench, bream and roach. Eels could not be sampled quantitatively but they must rank in the top five species in terms of biomass. Ordination and other analyses of community structure revealed several physicochemical and biotic factors that correlate with fish distribution and abundance. In particular, the presence of a floating plant mat in summer was associated with low oxygen concentrations at night and the absence of roach. The composition of fish communities in dykes contrasts in a number of ways with those recorded in local rivers and lakes (broads).
An Ichthyophonus‐typefungus in the deep‐sea pelagic fish Scopelogadus beanii (Günther) (Pisces: Melamphaidae)pathology, geographic distribution and ecological implications
Authors: Gartner J. V. , Zwerner D. E.
Published: January 2006

Parasitological examination of 400 specimens of the lower mesopelagic‐bathypelagic melamphaid fish Scopelogadus beanii (Günther) collected from throughout the species'geographic range in the Atlantic Ocean revealed cysts ranging in size from 1 to > 20 mm diameter in the livers of 50 individuals (12.5%). Histological preparations showed that the encysted material was an Ichthyophonus‐type fungus, which destroyed the liver tissue in infected individuals by progressive necrosis, the extent of which varied with cyst number and size. Infections were found primarily in individuals > 80 mm s.l. (size of sexual maturity in S. beanii), with a significantly higher rate of infection among females. Liver weight was significantly reduced in infected fishes. Body wet weights tended to be lower in infected females. Fish from the western Atlantic showed a significantly greater prevalence of infection (17.0%) than those from either the eastern (1.1%) or South Atlantic (7.1 %). Within the western Atlantic, individuals collected from the slope waters of the Mid‐Atlantic Bight showed a significantly higher percentage of infected individuals than those collected from more northerly areas (27.8% v. 9.9%, respectively); regional variations may be accounted for by differences in habitat and diet of S. beanii among these regions. The high percentage of infected individuals in the western North Atlantic, coupled with the pathogenic nature of the fungus, suggests the possible loss of reproductively competent individuals from the population of this region.
Structural characteristics of the epidermal mucosa in yellow and silver European eel, Anguilla anguilla (L.)
Authors: Saglio Ph. , Escaffre A. M. , Blanc J. M.
Published: January 2006

Histological observations were made on the distribution and concentration of the superficial mucous cells and on the thickness of the epidermis in immature yellow and in male and female silver eels. In all groups there was a decrease in the concentration of mucous cells from the anterior regions to the posterior regions, while the epidermis was thickest in the median parts of the body. Besides these common characteristics, a sexual dimorphism was shown: in silver eels the epidermis is thicker than in immature yellow eels; female silver eels have both the thickest epidermis and the greatest concentration of superficial mucous cells.

Results are discussed in the light of knowledge on the influence of environmental and endocrine factors on the structure and function of epidermal mucosa in teleosts.
Characterization of inflammatory neutrophils induced by bacterial endotoxin in the blood of eels, Anguilla australis
Authors: Hine P. M. , Wain J. M.
Published: January 2006

Peripheral blood neutrophils were studied in eels injected with phosphate buffered saline, bacterial lipopolysaccharide (LPS), carrageenan (CAR), LPS and CAR together (CAR/LPS(T)), CAR and LPS 4 days later (CAR/LPS(S)), zymosan and latex beads. All stimuli caused a left shift toward neutrophil immaturity but LPS‐elicited neutrophils, particularly in CAR/LPS stimulated eels, were often extremely basophilic, enlarged, vacuolated and had a large nucleus with poorly differentiated nuclear chromatin. These intensely basophilic neutrophils (IBN) had few granules and lower acid phosphatase and non‐specific esterase, but higher PAS levels, compared to normal neutrophils. Ultrastructurally, IBN showed loss of cytoplasmic content that gave a ragged appearance, the nucleus was often immature and many rough endoplasmic reticulum profiles restricted the distribution of reduced numbers of cytoplasmic granules. These features are attributed to asynchronous development, and IBN are compared with mammalian toxic neutrophils.
Aetiology of ‘red spot’ disease (vibriosis) with special reference to the ectoparasitic digenean Prototransversotrema steeri (Angel) and the sea mullet, Mugil cephalus (Linnaeus)
Authors: Rodgers L. J. , Burke J. B.
Published: January 2006

The ectoparasitic digenean trematode Prototransversotrema steeri was observed to infect a wide range of estuarine fish species of southern Queensland. The intensity and incidence of trematode infections on Mugil cephalus hosts were recorded and appeared to alter with the estuarine movement of the sea mullet host.

Highest trematode population densities were present on post‐spawning M. cephalus which had recently traversed brackish estuarine waters. Similarly, the highest prevalence of external ‘red spot’ lesions was also recorded from such fish.

The degree of complicity between P. steeri and ‘red spot’ bacterial pathogens was examined and is discussed. ‘Red spot’ or ‘ulcer disease’ is presented as a disease of multiple aetiology. It is suggested that some ectoparasites and a variety of primary and secondary bacterial pathogens may interact with environmental and behavioural factors to determine the prevalence of external lesions within each affected fish species.
Bacterial involvement in a saddleback disease of the reef silverside, At henna harringtonensis Goode (Pisces: Atherinidae) from Bermudan waters
Authors: Rand T. G. , Wiles M.
Published: January 2006

Saddle‐shaped skin lesions commonly occurring in both wild and captive Bermudan reef silversides yielded a mixed infection of motile and non‐motile Gram‐negative cells of Acinetobacter calcoaceticus, Aeromonas hydrophila, Pseudomonas sp., Vibrio parahaemolyticus and a myxobacterial‐like strain. Bacteria occurred as almost pure microcolonies and mixed clumps on proximal scale and fin ray surfaces, in intercellular epidermal spaces, on perimysium of fin erector muscle myomeres and on eroded dorsal fin rays and their intact membranes, but neither on healthy areas of the skin nor within muscle cells. Effects were epithelial destruction and liquefactive necrosis of myomeres, and raising and sloughing of Malpighian cells, scales and dermis. Host response was minimal, consisting of infiltration of a few lymphocytes and macrophages. The fish pathogenic dinoflagellate Amyloodinium ocellatum was seen in one fish with a saddle lesion and caused muscle cell lysis, as evidenced by cloudy cell swelling. Antibiotic sensitivity tests showed increased drug resistance with mixed bacterial types compared to that of single pure isolates. This suggests that alternatives to chemotherapy for control of bacterial fish diseases is appropriate, because most are probably caused by mixed infections.
Ploidy levels in silverside fishes (Atherinidae, Menidia) on the Texas coast: flow‐cytometric analysis of the occurrence of allotriploidy
Authors: Echelle A. A. , Echelle A. F. , DeBault L. E. , Durham D. W.
Published: January 2006

Flow cytometry of nuclear DNA fluorescence in erythrocytes, coupled with gene dosage assessments derived from electrophoresis of proteins, reaffirmed that the Menidia clarkhubbsi complex of unisexual atherinid fishes is diploid. Non‐recombinant hybrids between M. beryllina and M. peninsulae represented 18% (108 specimens) of the Menidia collected from three pools in the Copano Bay area and 9‐6% (42 specimens) of those from a pool on Galveston Island. Of those hybrids, 35 and 5%, respectively, were triploids. Zymograms indicated that the triploids either had two doses of genes from M. beryllina and one from M. peninsulas or they had one from the former species and two from the latter. The hybrids seem to be maintained primarily, if not entirely, by ongoing hybridization and back‐crossing of F1 hybrids to the parental species. Triploids apparently result from the combination of unreduced, diploid gametes from F1 hybrids with haploid gametes from either M. beryllina or M. peninsulae.
Immunocytochemical studies on immunoglobulin‐containing cells in the epidermis of rainbow trout Salmo gairdneri Richardson: influence of bath vaccination*
Authors: Peleteiro M. C. , Richards R. H.
Published: January 2006

The presence of immunoglobulin–containing cells in the epidermis of rainbow trout was traced, using post–embedding immunocytochemical techniques, in resin–embedded fragments of skin. Light microscopy observations (for which the PAP method was used)revealed the presence of immunoglobulin–containing cells in the epidermis, although no accurate identification was possible. Electron microscopy observations (employing gold–labelling) showed that, in spite of the poor preservation thought unavoidable to protect the antigenicity of the immunoglobulins, the positive cells were either lymphocyte–like cells or mucous cells. Anti–Vibrio anguillarium antibody was detected in the epidermal mucous cells of rainbow trout juveniles vaccinated by immersion, using an immunoenzymatic sandwich technique, modified for resin–embedded tissue. The possibility of the existence of a local immune system is discussed, considering the involvement of the mucous cells.
A new natural intergeneric cyprinid hybrid from the Jordan River drainage, with a key to the large barbine cyprinids of the southern Levant
Authors: Mir S. , Al‐Absy A. , Krupp F.
Published: January 2006

In Ain al‐Qunaiya. an isolated source within the Jordan River drainage basin of Jordan, several fishes were found to have characters intermediate between two cyprinid species. Barbus canis Valenciennes in Cuvier & Valenciennes. 1842 and Capoeta damascina (Valenciennes in Cuvier & Valenciennes. 1842). The hypothesis of their hybrid origin is advanced. A key to the large barbine cyprinids of the Jordan River system and their hybrids is given.
Prevalence of two site‐specific populations of Diplostomum spp. in eye infections of rainbow trout, Salmo gairdneri Richardson, from lakes in Washington State, U.S.A.
Authors: Bortz B. M. , Kenny G. E. , Pauley G. B. , Bunt‐ Milam A. H.
Published: January 2006

Two distinct site‐specific populations of Diploslomum spp., occurring concurrently in the lens and retina of naturally infected rainbow trout, were different morphologically. They represent separate populations epidemiologically. The lens and retina metacercariae did not differ immunologically when tested by an enzyme‐linked immunosorbent assay against immune rabbit and trout antisera. Antibody titres became positive by September 1982 in a natural population of yearling rainbow trout infected with lens and retina metacercariae and remained positive for at least 8 months. The antibodies formed may offer protection against reinfections with Diplostomum spp. cercariae.
Distribution and variation in the growth of roach, Rutilus rutilus (L.), and dace, Leuciscus leuciscus (L.), in a river catchment in south‐west England
Authors: Cowx I. G.
Published: January 2006

The distribution and growth of roach and dace in the R. Exe catchment was studied. Distribution conformed to the classic theories of zonation, although human interference extended or reduced the range of species. Distinct differences were found in the growth rates of roach and dace between different regions of the catchment. Both species achieved their fastest growth in zones where the river topography portrayed their ‘preferred’ habitat characteristics, i.e. the fast‐flowing middle and slow‐flowing lower reaches for dace and roach, respectively. Female roach were found to grow considerably faster than male fish, whilst no sexual differentiation in growth rates was found in dace. Considerable fluctuations in year class strength were observed in both species.
Predation on hatchery‐reared and wild smolts of Atlantic salmon, Salmo salar L., in the estuary of River Orkla, Norway
Authors: Hvidsten N. A. , Lund R. A.
Published: January 2006

Predation on wild and hatchery‐reared Atlantic salmon smolts was studied in the estuary of River Orkla. Cod and saithe congregating in the estuary were the most serious predators on smolts. There was no difference between the mortality rates of wild and hatchery‐reared smolts. Predation by cod was estimated at 20%. No evidence was found to indicate selective predation on the smallest wild and hatchery‐reared smolts.
Life styles and patterns of development of gills and muscles in larval cyprinids (Cyprinidae; Teleostei)
Authors: El‐Fiky N. , Wieser W.
Published: January 2006

A morphometric study of gill structures and of the body musculature during the first weeks after hatching was carried out on larvae of six cyprinid species: Leuciscus cephalus, L. leuciscus, Rutilus rutilus, Alburnus albumus, Chondrostoma nasus and Abramis brama. In all species a unicellular layer of red muscle fibres covers the central muscle mass; this layer is of greatest extent shortly after hatching but diminishes gradually in mass by contracting towards the lateral region of the body until it merges with (or gives rise to) the adult red muscle fibres proper. There is a close relationship between the rate of differentiation of gill structures and the rate at which the larval red muscle layer disappears, the pattern of this relationship reflecting the life style of the species. The longer the larvae delay the start of their free‐swimming existence after hatching (which in A. alburnus may be as long as 10 days) the longer does the red layer of muscle fibres serve as the organ of gas exchange and the longer is gill development suppressed. It appears that the metabolism of the swimming muscles is almost entirely aerobic so long as gas exchange takes place across the whole body surface, the glycolytic capacity of the central muscle mass developing only slowly in conjunction with the switch from red layer to gills as the major respiratory organ.
Size‐selective overwintering mortality in the sand smelt, Atherina boyeri Risso, and its role in population regulation
Authors: Henderson P. A. , Holmes R. H. A. , Bamber R. N.
Published: January 2006

The fat laid down as a winter reserve by O‐group sand smelt, Atherina boyeri, was found to be size‐dependent. The larger, earlier‐spawned fish lay down more fat prior to the onset of winter. During the winter the fish do not feed for some 100 days and rely on this fat for energy; laterspawned O‐group fish (<59 mm s.l. in November) have insufficient fat reserves and starve to death in a normal winter. This loss of the smallest 46% of the O‐group is shown as an increase in the mean size of the O‐group over the winter period. Older sand smelt age classes have more than sufficient fat reserves for overwintering. There is thus a clear advantage in spawning early in the season, and any restriction on spawning ground availability at that time will result in overall population regulation. This conclusion supports the hypothesis that the density‐dependent control on population size in the sand smelt is a limitation on the number of fish which can spawn at the optimum time.
Measurement of regurgitation in feeding studies of predatory fishes
Authors: Treasurer J. W.
Published: January 2006

Regurgitation of stomach contents in the predatory perch and pike captured in gill nets could be readily identified and occurrence measured. Stomachs following regurgitation, as opposed to true ‘empty’ stomachs, were large, distended, with a thin wall and little internal ridging. The mean percentage of genuinely empty stomachs over a 22‐month period in perch was 20–21 % and in pike 7–10%. Regurgitation in perch was rare (<9% stomachs), normally only partial and restricted to water temperatures > 21°C: gill netting is therefore a legitimate means of sampling perch in food studies. In pike the sum of partial and complete regurgitation was important, with mean annual values in two lakes of 48 and 50%, and up to 84% in summer samples; it was related to water temperature (x) and described by the significant relationship y= 20.63+x 2.84, but was unrelated to fish length and gill net mesh size. Food studies of predatory fishes using gill nets as a capture method should take account of regurgitation. Further information is required on the extent of regurgitation when other sampling methods are used.
Two new indices for stomach content analysis of fishes
Authors: Mohan M. V. , Sankaran T. M.
Published: January 2006

Two indices, Simple Resultant Index (Rs) and Weighted Resultant Index (RH), are proposed for enabling the analysis of stomach contents of fishes. The indices are based on percentage occurrence and percentage volume, as in the case of the Index of Preponderance. Possible graphical representation of the indices helps towards understanding the relative representation of the two contributing parameters. The weighted index is, in particular, a means of comparison, grading food items in the order of importance.
Gastric digestion and evacuation in whiting, Merlangius merlangus (L.)
Authors: Bromley P. J.
Published: January 2006

Three meal sizes of sandeels were fed to whiting in order to monitor the evacuation of food out of the stomach. The stomach contents were sampled at intervals after feeding, using a stomach pump. In such experiments, the proportion of fish with empty stomachs tends to increase with time and, since stomach contents are limited to zero or positive values, the variance of the stomach contents becomes censored at zero. This tends to produce a curved relationship between mean stomach content and time, which gives the impression that evacuation rate slows down at low levels of stomach fullness. By taking account of censoring, it was shown that the evacuation curve generated for whiting was consistent with and could be generated from a linear model in which the rate of gastric evacuation exhibited by the fish was constant and independent of meal size, level of stomach fullness and time after feeding. The parameters of the linear model were estimated by maximum likelihood and then applied in a second model to predict the observed mean stomach content. The average gastric evacuation rate of whiting of mean weight 268 g at 10°C was 0.31 g h−1.
Temporal and spatial segregation of spawning in sympatric populations of Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L.
Authors: Heggberget T. G. , Haukebø T. , Mork J. , Ståhl G.
Published: January 2006

Based on data from Norwegian streams with sympatric populations of Atlantic salmon and brown trout, it is suggested that temporal segregation is the main mechanism segregating Atlantic salmon and brown trout during spawning. Peak spawning of trout was about 15 days earlier than that of salmon. Physical factors, such as water depth, water velocity and distance from the river banks segregate spawning sites of salmon and trout poorly. Gravel sizes of the redds of salmon and trout were significantly different, though with a considerable overlap, and mean egg depth of salmon and trout were 0.18 and 0.12 m, respectively, probably attributable to the different size of spawners of salmon and trout. None of the temporal or spatial parameters analysed segregate spawners of salmon and trout completely. Species determination of eggs and alevins from the redds showed no interspecific superimposition of redds. It is, therefore, concluded that low survival of hybrids after hatching does not explain the low frequency of hybrids observed in sympatric populations of salmon and trout.
Kidney morphology in sturgeons: a microdissectional and ultrastructural study
Authors: Gambaryan S. P.
Published: January 2006

The anatomy and ultrastructure of nephrons were studied in various euryhaline and freshwater sturgeons. Microdissection failed to reveal marked differences in the nephron structure between freshwater and euryhaline fishes which might be considered as specific adaptations to the salinity of the environment. Some adaptive changes in the nephron structure were revealed by electron microscopic examination. The glomerular basal membrane is thicker in euryhaline sturgeons than in the freshwater sterlet. The processes of mesangial cells penetrating the basal membrane are much more numerous in fishes caught in the sea than in those from fresh water. Euryhaline sturgeons exhibit a great variability in the ultrastructure of epithelial cells of proximal and distal tubules. The number of mitochondria‐rich cells possessing well‐developed basolateral foldings is significantly higher in fishes caught in the sea. In the freshwater sterlet the ultrastructure of the epithelium of proximal and distal tubules resembles that in freshwater teleosts.

Comparison was made of the kidney morphology and ultrastructure in sturgeons, elasmo branchs and bony fishes. It is speculated that in sturgeons the adaptation to varying salinity is achieved by changes in the ultrastructure of glomeruli and differentiation of the cells of the tubular epithelium.
Gastric emptying in cod, Gadus morhua L.: effects of food particle size and dietary energy content
Authors: dos Santos J. , Jobling M.
Published: January 2006

Whole herring, Clupea harengus, were digested and emptied from cod stomachs much more slowly than meals of minced herring, showing that prey integrity is an important factor controlling emptying. Increasing the energy content of the minced herring by addition of fish meal and oil led to a reduction in the percentage of the meal emptied in the 24 h subsequent to feeding, but rates of energy throughput on the enriched herring diet were high. The physical form of the diet appears to be more important than energy content in the control of gastric emptying in cod. The results are discussed with respect to possible effects of dietary type on absorptive and metabolic processes.
Effects of anaesthesia on the chemosensory behaviour of Pacific salmon
Authors: Quinn T. P. , Olson A. F. , Konecki J. T.
Published: January 2006

As Lewis et al. reported in J. Fish Biol.26, 355–358 (1985) that the anaesthetic tricaine methanosulphate (MS 222) damaged the olfactory epithelium of channel catfish, two assays were used to determine whether MS 222 or 2‐phenoxyethanol (an alternative anaesthetic) influenced subsequent olfaction‐mediated behaviour. Tests revealed that the homing of adult chinook salmon, Oncorhynchus tshawytscha, and the l‐serine avoidance response of juvenile coho salmon, O. kisutch, were not altered by anaesthesia.
Observations on the nesting habits of Oreochromis mossambicus (Peters) (Pisces: Cichlidae) in Sri Lankan reservoirs
Authors: de Silva S. S. , Sirisena H. K. G.
Published: January 2006

The nest‐building characteristics of Oreochromis mossambicus (Peters) were studied in five manmade lakes (reservoirs) Sri Lanka. The nests were always found in clusters (arenas) and were generally located in or near coves and/or bays in shallow water. The density of nests in an arena varied between arenas in a reservoir and between reservoirs. The overall mean density of nests ranged between 0.47 and 6.31 m 2 in the five reservoirs. The nests ranged from 11 to 110 cm in diameter, two size groups of nests being recognizable: small, with diameter 10–50 cm, and large with diameter >50 cm. At any nesting site only one size group of nests was found.

Nest diameter (ND) was curvilinearly related to mean nest density (D) and linearly to mean distance between nests (Dis), the respective statistical relationships being

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The diameter of nests was also related to nest depth (Dep) as

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There was no apparent relationship between nesting characteristics and morphometric characters of the reservoirs.
Experimental analysis of the thermal and salinity preferences of glass‐eels, Anguilla anguilla (L.), before and during the upstream migration
Authors: Tosi L. , Sala L. , Sola C. , Spampanato A. , Tongiorgi P.
Published: January 2006

During their upstream migration European glass‐eels, Anguilla anguilla (L.), encounter a series of varying environmental situations. The migration requires a sequence of physiological adaptations determined by the different chemico‐physical conditions they meet. Temperature and salinity are two of the most important factors. It is reasonable that glass‐eels may utilize them as cues to orientation. Laboratory experiments were designed to elucidate the thermal and salinity preferences of glass‐eels. These were assessed by examining the choices of specimens caught either at sea and then kept in salt water (33%), or in the Arno river and then reared in fresh water. Water flows, triggering the rheotactic reaction, prompted glass‐eels to choose between two different salinities and/or temperatures. The results confirm the preference of glass‐eels for flows whose temperature does not differ from that of acclimation. Specimens tested towards two water flows, both at different temperatures from that of acclimation, preferred the colder. Fresh water was usually preferred to salt water, this preference being not so marked in the case of the glass‐eels caught at sea and thus not yet adapted to fresh water. Clear‐cut choices were recorded when one of the tested flows presented both the preferred temperature and preferred salinity. When only one of the two parameters reproduced the preferred situation, the choices were differently affected by temperature and salinity at different values of temperature. When the temperature of both flows was below 11–12°C, glass‐eels preferred fresh water; at higher temperatures the colder of the two flows was preferred, even if salty.
Early sexual maturation in males of wild sea trout, Salmo trutta L., inhibits smoltification
Authors: Dellefors C. , Faremo U.
Published: January 2006

Precocious maturation among wild sea trout, Salmo trutta (L.), was studied in two small streams in south‐western Sweden. The proportion of parr males varied between 17.9 and 57.0%. Parr males and immature individuals of the same age were compared with respect to length distribution, migratory tendency and seawater tolerance. Precocious males were, on average, longer than immature fish. Marking and recapture showed a reduced or inhibited migration tendency of parr males. The seawater tolerance of these was also consistently lower than for juveniles. The seasonal pattern in osmoregulatory ability was similar for both categories, with a peak during the smolt run.
Seasonality, depth and habitat distribution of breeding males of Oreochromis spp., ‘chambo’, in Lake Malawi National Park
Authors: McKaye K. R. , Stauffer J. R.
Published: January 2006

The temporal pattern of breeding by chambo, Oreochromis spp., and the vertical and horizontal distribution of territorial males at the Golden Sands‐Chembe beach were examined in the Cape Maclear region of Lake Malawi National Park. The breeding season began in September and ended in April, and the number of breeding males between 3 and 15 m was approximately 25 ha. Along the beach studied, the highest concentrations of nests were found at the ends of the beach near rocks, and the lowest number of breeding males occurred in front of Chembe village

Results from experimental gill netting demonstrated that the catches of chambo within the 100‐m Lake Malawi National Park ‘no fishing zone’ were identical to those outside the 100‐m zone, suggesting that fishermen would suffer little or no loss in catch by being encouraged to fish more than 100 m from the shore. Such a reduction in fishing and disturbance of the shallow water breeding grounds would probably enhance the chambo fishery. Preliminary data are provided on the chambo nest forms found in the Cape Maclear region, and further research is suggested to resolve the question of how many species comprise the genus Oreochromis in Lake Malawi.
Otolith shape discriminates between juvenile Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L.
Authors: L'Abée‐Lund J. H.
Published: January 2006

Otoliths of Atlantic salmon, Salmo salar L., are more slender than the otoliths of brown trout, Salmo trutta L. Discriminant analysis on otolith measurements of juvenile Atlantic salmon and brown trout from four river systems revealed a discriminant function which distinguished more than 94% of the cases. This function was tested by using data from a fifth river with cohabiting Atlantic salmon and brown trout: all Atlantic salmon and 91 % of the brown trout were correctly classified.
Movement rhythms in juvenile Atlantic salmon, Salmo salar L.
Authors: Thorpe J. E. , Morgan R. I. G. , Pretswell D. , Higgins P. J.
Published: January 2006

Nocturnal downstrean migration of juvenile Atlantic salmon is usually interpreted as increased locomotor activity. The frequency of downstream passages of 0–1 + salmon in an endless stream channel was greater by night than by day in both smoking and non‐smolting fish in autumn and spring. Movement increased at dusk, and decreased after dawn. Mature male 1 + fish moved slightly less than immatures in October, but significantly more in November. Total movement frequency was lower at full moon than at other moon phases, and movement was reduced when the moon was up. Under turbid conditions by day, the threshold water velocity inducing nett downstream movement was 8.2 cm s−1, and the relative velocity of fish swimming downstream was never more than one third that of fish holding station at the normal maximal flow of 25–30 cm s−1.

At the end of their first growing season in October, fish which had been offered food continuously through 24 h did not differ in size from those fed by day only, but the latter were significantly larger than those offered food only at night.

We conclude that: (1) the fish fed actively by day, and not by night; (2) station‐holding represented activity, and downstream nocturnal movement represented relative inactivity (displacement) which occurred on loss of visual orientation, hence migration resulted from reduced activity; (3) lack of displacement in early autumn has adaptive value for maturing fish, but not for non‐spawners.
Effect of temperature on the deformability of a lamprey, Entosphenus japonicus, and Pacific salmon, Oncorhynchus keta, red blood cells, studied using a modified filtration method
Authors: Hughes G. M. , Koyama T.
Published: January 2006

The rates of filtration through Nuclepore filters (5 or 8 μm) of blood from lampreys and Pacific salmon have been studied using a method which visualizes the flow pattern. From these measurements, passage times for single red blood cells have been calculated and serve as an index of their deformability. The deformability increases as temperature is raised in vitro, but even at 5°C the passage time of lamprey blood is relatively rapid. The increase in deformability with a rise in temperature is small relative to that found in other fish such as yellowtail and carp.

The distribution of red cell volumes has shown the presence of a secondary peak for salmon blood taken during surgery which is reduced following recovery, the main peak being at a lower volume.
Fish impingement at estuarine power stations and its significance to commercial fishing
Authors: Turnpenny A. W. H.
Published: January 2006

The abstraction of cooling water at power stations sited on tidal waters inevitably leads to mortalities of some fish which are drawn in with the cooling water supply and become impinged on the intake screens. These fish are predominantly 0‐ or I‐group juveniles which, owing to their small size, are unable to resist intake currents.

Commercial fishermen often object to the fact that juvenile fish are killed in this way. Their concern stems from the fact that, in order to protect stocks, commercial fishing is restricted to fish which are above a statutory minimum landing size, whereas the majority of fish killed by impingement are below this size.

This paper considers the significance of impingement mortalities at estuarine sites in Britain for six commercially important species: cod, Gadus morhua, whiting, Merlangius merlangus, plaice, Pleuronectes platessa, dab, Limanda limanda, sole, Solea solea and herring, Clupea harengus. Life tables are used to establish expected survival trajectories for each species and to compute reproductive potential. Each fish killed on intake screens is then considered in terms of the fraction of the reproductive potential of a single adult at maturity, and is ascribed an ‘adult equivalent’ value. Total catches of mixed juveniles and adults are then presented as ‘adult equivalent’ values. The results are then compared with commercial landings data and it is shown that catches by power stations are trivial in comparison with commercial landings.
Movements of juvenile Dover sole, Solea solea (L.), in the Tamar Estuary, South‐western England
Authors: Coggan R. A. , Dando P. R.
Published: January 2006

Solea solea start to appear in the Tamar Estuary in April–May when they are 10 mm long. The majority of young sole move into the estuary in June–July. Most sole leave the estuary towards the end of their second year in October–November, when they have reached a total length of 150–200 mm. The young O‐group fish remain in the main channel, whereas the I‐group move with the tide onto the mud‐flats.

Approximately 7000 fish were marked by freeze‐branding or dye‐injection. The recaptures showed that there was an up‐estuary migration in May–June. Most of the recaptures were taken at the site of original capture and there was only a limited movement of fish between adjacent mud‐flat areas. Average growth rate tends to be greater in sole inhabiting the upper reaches of the estuary.
Migratory behaviour of adult cisco, Coregonus albula L., in the Bothnian Bay
Authors: Enderlein O.
Published: January 2006

The population of adult cisco in the Bothnian Bay consists of a number of spawning populations. Each one of these returns to the same inshore area for spawning every autumn. In the summer these populations are mixed and occur mainly offshore. These are the main conclusions of an experiment in which cisco were marked with Carlin‐type tags. The cisco were caught mainly in fyke nets both in the summer and in the autumn and released after tagging in the area where they had been caught. Fish tagged in the autumn and recaptured in the autumn one or more years later showed a strong affinity to the point of release, while fish from the same group recaptured in the summer had migrated far from the release site. The distribution of cisco that were tagged in the summer and caught in the autumn showed no correlation with the release site.
Natural hybridization between Atlantic salmon, Salmo salar, and brown trout, Salmo trutta, in northern Spain
Authors: de Leaniz C. Garcia , Verspoor E.
Published: January 2006

Hybrids between Atlantic salmon and brown trout were detected in two of four watersheds studied in northern Spain. The proportions of hybrids in samples of 'salmon’ranged from 0 to 7–7% but they were not significantly heterogeneous among locations, resulting in a mean hybridization rate of 2–3%. This is the highest rate of natural hybridization so far reported and is significantly greater than rates observed elsewhere in Europe.
Population dynamics of brown trout, Salmo trutta L., in a tributary in Brittany (France): spawning and juveniles
Authors: Bagliniére J. L. , Maisse G. , Lebail P. Y. , Nihouarn A.
Published: January 2006

The colonization by both resident and migrating spawner populations of brown trout and the characteristics of resident and migrating juveniles derived from the two populations have been studied in a brook and its tributary over 4 years. Resident trout spawns mainly in the upstream part of the brook and migrating trout in the downstream part. There are density and growth variations for the two age classes (0+ and 1 +) of juveniles in autumn according to the year and the environment. In the brook, the population of 0 + fish increases from downstream to upstream while the density of other age classes decreases. The migrating juvenile population of the brook changes annually and consists mainly of 1 s (one summer) individuals coming from the upper part. These individuals migrate generally in autumn and winter while young trout produced in the middle and downstream parts of the brook migrate mainly in the spring. The emigration process of the 0 + population decreases markedly from upstream to downstream and appears to be independent of the autumn length and sex ratio. In the tributary, most trout are 0+ years old, the population structure is different, and no migrating fish is observed. The results are discussed and a colonization strategy of the brown trout population in this brook is suggested.
The palatability of amino acids and related compounds to rainbow trout, Salmo gairdneri Richardson
Authors: Jones K. A.
Published: January 2006

Using a behavioural assay, the palatability of urea, taurine, betaine and the 20 common amino acids (L‐isomers) to rainbow trout was determined. The trout responded positively only to aqueous solutions of leucine, isoleucine, proline, phenylalanine, tryptophan, methionine, glutamate, arginine, taurine and urea. Proline, the most effective compound, was active at 10 ‐4 m but not 10‐5m. Palatibility was not directly related to test solution pH; concentration and molecular structure apparently played a greater role. There is good, though not perfect, agreement between the behavioural results obtained here and published electrophysiological data on the palatal sensitivity of rainbow trout to these substances.
The influence of three unchanging photoperiods on growth and parr‐smolt transformation in Atlantic salmon, Salmo salar L.
Authors: Stefansson S. O. , Naevdal G. , Hansen T.
Published: January 2006

Groups of pre‐smolt Atlantic salmon were reared under three experimental photoperiods. Growth rate was significantly enhanced under 24 h of light: 0 h of darkness per diem (24 L: 0 D) compared with 16 L: 8 D and 8 L: 16 D from early January to early May. From the beginning of May until the termination of the experiment on 27 May, growth rate was highest under 8 L: 16 D.

All groups developed bimodal length‐frequency distributions during the experiment. The proportion of the population in each of the two growth modes was significantly affected by photoperiod treatment.

The level of plasma cortisol increased significantly from February to May. There were no differences in levels of plasma cortisol among photoperiod treatments.

Judged by development in plasma cortisol, changes in condition factor and external appearance, the parr‐smolt transformation was not completed under any of the experimental photoperiods.
The effect of ultrasonic tags on the growth rates of Atlantic salmon, Salmo salar L., parr of varying size just prior to smolting
Authors: Greenstreet S. P. R. , Morgan R. I. G.
Published: January 2006

The attachment of dummy, ultrasonic, acoustic tags, of the Stirling Mk. VI design, to pre‐smolt Atlantic salmon parr significantly affected fish growth rates. Fish less than 160 mm in length lost weight and showed no change in length. Fish over 160 mm in length put on weight, though at a rate significantly lower than that of untagged controls. For fish between 160 and 180mm in length, the increase in length was significantly smaller in tagged fish than in untagged controls. Over 180 mm in length, no difference could be detected in the length gains of tagged and untagged fish.

Smaller tagged fish gave up maintaining station and showed signs of distress at an earlier stage in the experiment than larger tagged fish. Tag‐related mortality was inversely related to fish size. All but two of the control fish survived the experiment and continued to maintain station throughout.

The results suggest that the minimum length of Atlantic salmon parr on which this design of acoustic tag could be employed is 160 mm, and that caution is needed in the interpretation of track lengths longer than l0 daysof parr in the size range 160–180 mm.
Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature
Authors: Walsh W. A. , Swanson C. , Lee C.‐S. , Banno J. E. , Eda H.
Published: January 2006

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk‐sac, preflexion, flexion and post‐flexion larval stages.

Oxygen uptake rates of eggs increased linearly from 0.024 μl O2 per egg h‐1 (0·323 μl O2 mg‐1 dry wt h‐1) by blastulae to 0·177 μlO2 per egg h‐1 (2·516 μlO2mg 1dry wth‐1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%0).

Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O2 per larva h‐1 shortly after hatching to 18·880 μl O2 per larva h‐1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass‐specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O2 mg 1dry wt h‐1).

Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk‐sac larvae (Q10= 2·75) than in postflexion larvae (Q10= 1·40).
Histological structure of the intestine and pyloric caeca of the green sunfish, Lepomis cyanellus Rafinesque
Authors: Williams J. A. , Nickol B. B.
Published: January 2006

A histological study was made of the intestine and pyloric caeca of green sunfish, Lepomis cyanellus (Centrarchidae). The intestinal and caecal walls are histologically very similar, consisting of a mucosa (epithelial layer), submucosa (lamina propria and stratum compactum), muscularis (circular and longitudinal layers) and the serosa. Cellular constituents of the mucosal layer include absorptive, columnar epithelial cells, mucous‐secreting goblet cells, and various leucocytes, the majority of which are lymphocytes. Other than relative size and the entrance of the bile duct at the base of the first caecum, no difference was found among caeca.

When fish were nutritionally stressed, a greater variety and number of leucocytes and shifts in the numbers of lymphocytes and goblet cells of the mucosal layer were the only observable effects.
Sexual dimorphism in the energetics of reproduction and growth of North Sea plaice, Pleuronectes platessa L.
Authors: Rljnsdorp A. D. , Ibelings B.
Published: January 2006

The chemical composition and energy content of North Sea plaice during the spawning period were examined in mature males and females and in immature fish, to study differences in the allocation of energy over reproduction and somatic growth between the sexes.

At the beginning of the spawning period mature males and females had equal dry weights of lipid that were 70% higher than in immatures. Protein content in mature males was equal to that in immatures but was 23 % higher in mature females. Immature males and females did not differ in chemical composition. At the end of the spawning period, spent and immature fish had equal lipid contents, but protein content in spent females was 10% lower than in spent males, and 17% lower than in immatures. Gross energy content of the body decreased by 44% (65·2 to 36·3 J cm‐3) in mature females, 27% (55·0 to 40·OJ cm‐3) in mature males, and 9% (48·7 to 44·2J cm‐3) in immatures. Energy content of plaice eggs was estimated at 6·60 kJ per 1000 eggs.

Reproductive investment was estimated from the energy loss during the spawning period and included the energy of sex products and spawning metabolism. Somatic growth comprised the annual increase in energy content of fish. The pattern of energy allocation over reproduction and somatic growth differed between males and females. Males started their reproduction at a smaller length and a younger age and allocated a higher proportion of the available energy into reproduction than females. Available energy resources for somatic growth and reproduction (surplus production) were equal between the sexes up to a length of about 30 cm. Beyond this length male surplus production levelled off whereas female surplus production continued to increase. The differences in surplus production and the allocation patterns are discussed.

For female plaice the energy allocated into egg production was estimated as between 48 and 64% of the total amount of energy lost during spawning. The remaining energy is used for metabolism during the spawning period, yielding an estimate of the metabolic rate of mature females of between 6·4 and 9·1 kJ day‐1. A maximum estimate of the metabolic rate of mature males was 7·4 kJ day‐1.
The food and feeding relationships of black oreo, Allocyttus niger, smooth oreo, Pseudocyttus maculatus, and eight other fish species from the continental slope of the south‐west Chatham Rise, New Zealand
Authors: Clark M. R. , King K. J. , McMillan P. J.
Published: January 2006

The food and feeding habits of black oreo and smooth oreo sampled at depths of 600–1200 m from the south‐west Chatham Rise in 1983 are described, with notes on prey of eight other fish species. All these fish species fed benthopelagically. Black oreo preyed on hyperiid amphipods, salps and natant decapod crustaceans; smooth oreo on salps and amphipods. Dietary composition of both species changed with size of fish. Aspects of feeding relationships between the fish species were examined including dietary similarity and prey‐size selection. Findings are compared with results of research on other New Zealand deepwater fish species.