bluuebunny/crossref_metadata_2025 huggingface dataset:
Movements of brown trout, Salmo trutta, and juvenile Atlantic salmon, Salmo salar, in a coastal stream in northern Norway
Authors: Hesthagen T.
Published: January 2006

Movements of resident brown trout (age 2+ to 9+ years) and young Atlantic salmon (age 1+), stocked as fry, were studied in July, August and September in a coastal stream in northern Norway. Between 85 and 89% of the brown trout were recaptured in the study area (346m, 1326m2) within 45m of their release point throughout the investigation period. Most specimens had moved less than 150m. Trout movements were related to local variation in density. Trout occupying those sections of stream with the lowest fish densities (5.3–10.9 fish 100m−2) had a significantly lower movement rate than fish from sections with densities between 13.7 and 31.5 fish 100m−2. Trout that moved from their marking section were significantly larger than specimens that did not leave their original site. There was a significant correlation between permanence of station each month and the mean water level that month. The majority of the trout (47%) were caught at undercut stream banks or at sites in the proximity of these. A decrease in water level during the study period resulted in a high loss (36%) of such habitat, probably forcing some individuals to move. The recapture data indicate that the trout population consists of one small (c. 15–20%) mobile, and one large sedentary component.

Young salmon displayed high station permanence in July and August (93% and 96%). However, in the autumn they exhibited a significant downstream movement, and only 73% were recaptured within their release section. This movement was significantly higher for larger specimens, and is thought to occur because of a pre‐winter change in habitat, initiated by a decline in stream temperature. In contrast to trout, salmon in sections containing the lowest densities (22.0–25.0 fish 100m−2) did not show significantly lower movement rates when compared with salmon at higher densities (32.2–46.3 and 51.8–60.6 fish 100m−2). The spatial distribution of young salmon indicated the formation of territorial mosaics over the stream bed, which are thought to reduce intraspecific competition.
Comparative study on the induction of triploidy in tilapias, using cold‐ and heat‐shock techniques
Authors: Don J. , Avtalion R. R.
Published: January 2006

Optimal conditions for the induction of triploidy in two different species of tilapia, Oreochromis aureus and Oreachromis niloticus, were determined using either heat‐shock or cold‐shock techniques. These treatments were applied at conditions that were separately determined for each species. Embryos of these two species were found to differ in their response to heat‐shock, but not to cold‐shock treatments. The yield of triploid O. niloticus embryos induced at 40.5°C at the zygotic age of 3‐5 min did not exceed 13%, in contrast to 60% obtained in O. aureus (heat‐shocked at 39.5°C at zygotic age of 3 min). The possibility that the different responses of the two species to heat shock is maternally inherited was supported by the fact that the two‐way F1 hybrids also responded in a similar maternally dominant manner. Although the induction of triploidy using heat shock was possible only within a narrow range of zygotic ages (2.5–3.5 and 3.5–4.5 min for O. aureus and O. niloticus, respectively), the induction of triploidy using cold‐shock treatment (11°C for 60 min) could be achieved within a wider range of zygotic ages (0–15 min). A satisfactory yield of troploids in the two species (50 and 60% in O. niloticus and O. aureus, respectively) was obtained using this technique. The possible interpretation of these results, that triploidy could be induced by interfering at two distinct meiotic cell‐division stages, is discussed. It is concluded that the cold‐shock technique is more advantageous for inducing triploidy in O. niloticus, whereas both cold‐shock and heat‐shock techniques are equally efficient in O. aureus.
The size of a vendace, Coregonus albula L., stock in a deep lake basin monitored by hydroacoustic methods
Authors: Jurvelius J. , Lindem T. , Heikkinen T.
Published: January 2006

An acoustic estimate of the number and biomass of a vendace stock (age >2 + years) in a deep basin of Lake Karjalan Pyhäjärvi was made in August 1985. The acoustic data were collected at night during the summer stagnation. The vendace were on the lake bottom during the day and rose by midnight to the hypolimnion; they did not rise to the thermocline or water layers above it. In the research area the mean number of vendace was 1900 fish ha −1 and the mean biomass was 76 kg ha −1. Total vendace biomass was 151 in the whole 200‐ha research area.
Lymphocytopenia and the overwinter survival of Atlantic salmon parr, Salmo salar L.
Authors: Pickering A. D. , Pottinger T. G.
Published: January 2006

The overwinter mortality rate of underyearling S2 Atlantic salmon parr (fish that will remain in fresh water for at least two years prior to smoltification) was almost ten times greater than that of S1 parr (fish that will smoltify after 1 year in fresh water) kept under similar conditions. The loss of condition (K factor) of the S2 parr was proportionally greater than that of S1 parr during the early winter months and this coincided with a marked lymphocytopenia and thrombocytopenia in the S2 parr. Limited evidence indicates that S2 parr have chronically elevated blood cortisol levels during the winter months. It is suggested that chronic stress resulting (in part) from nutritional deficiency has a debilitating effect on the defence systems of these fish. The ultimate cause of mortality in most cases was bacterial fin‐rot and/or fungal (Saprolegnia) infection. These findings are discussed in relation to the habitat requirements of overwintering salmonid fish.
Population differences in the reaction of minnows to alarm substance*
Authors: Levesley P. B. , Magurran A. E.
Published: January 2006

Experiments showed that minnows, Phoxinus phoxinus, sympatric with pike, Esox lucius, responded more vigorously to alarm substance than minnows from a population with no experience of pike predation in the wild. Minnows from the pike‐sympatric (Dorset) population were more likely to hide and less likely to risk feeding than their pike‐allopatric (Gwynedd) counterparts. The reaction to alarm substance in the pike‐sympatric population was further increased when it was presented along with the visual stimulus of a ‘stalking’ model pike. When the Dorset minnows experienced both alarm substance and the pike model together they reduced their inspection behaviour to a level below that of the Gwynedd minnows. Minnows from the Gwynedd (pike‐allopatric) population displayed increased levels of shoaling in the treatments in which alarm substance was used.
Sound production by the gudgeon, Gobio gobio L., a common European freshwater fish (Cyprinidae, Teleostei)
Authors: Ladich F.
Published: January 2006

Acoustic signals emitted by the gudgeon are described and the context of sound production is considered.

In aquaria, gudgeons produce creaking sounds of differing duration, which are always built up of single bursts. Each burst is composed of a series of rapidly repeated short pulses. Vocalization is correlated with the level of activity: it increases at higher temperatures and decreases when fish are disturbed. After acclimatization to the aquarium, fish which formerly showed a diurnal pattern of activity became active at all times of the day and night. Gudgeon called as a reaction to digging by other members of the group and a variety of disturbances, the latter including being touched or hindered by a conspecific or being frightened by the sudden movement of another fish. The fact that only certain interactions in a gudgeon shoal are accompanied by sound production is discussed.
Effects of ration, temperature and body size on the body composition, energy content and condition of the minnow, Phoxinus phoxinus (L.)
Authors: Cui Y. , Wootton R. J.
Published: January 2006

The effects of ration and temperature on the body composition, energy content and indices of condition of the minnow. Phoxinus phoxinus (L.) (Cyprinidae). were studied experimentally. Five ration levels over the range starvation to ad libitum and five temperatures over the range 5–15°C were used. The fish weighed 1‐5‐4 g. At each temperature, the relative dry matter content, lipid content and energy content increased with increased ration. The response of the protein content to ration was temperature‐dependent. Temperature had a significant effect on body composition and energy content, but this effect was irregular. The Fulton condition factor was less sensitive to ration than the wet or dry liver‐somatic index. Temperature had a significant effect on the condition factor and liver indices. Significant, positive correlations were found between growth rate, lipid content and the indices of condition. The liver indices were better predictors of growth rate than the condition factor or lipid content and may provide useful information on the physiological condition offish in field studies.
Sediment processing by the surgeonfish Ctenochaetus striatus at Moorea, French Polynesia
Authors: Nelson S. G. , Wilkins S. DeC.
Published: January 2006

The sediment‐feeding surgeonfish Ctenochaetus striatus was found to reduce the sizes of ingested carbonaceous particles. The mean sizes of particles in stomach samples of the surgeonfish were smaller than those from areas where the fish were observed feeding. The particle sizes in the rectal contents of the fish were smaller than those in the stomach samples. The sediment‐feeding activities of this and related surgeonfishes are likely to have a local impact on the particle‐size distributions of sediments in reef and lagoon habitats. The assimilation efficiencies of the fish were estimated by the ash‐ratio method to be 20% for total organic matter and 37% for nitrogen.
Influence of gut morphology, sensory cues and hunger on feeding behaviour of spangled perch, Leiopotherapon unicolor (Günther, 1859), (Percoidei, Teraponidae)
Authors: Gehrke P. C.
Published: January 2006

The morphology of the alimentary canal, feeding technique and responses to sensory cues were investigated in Leiopotherapon unicolor. The small conical teeth on the jaws and pharynx, simple Y‐shaped stomach and short gut of L. unicolor are characteristic of opportunistic carnivorous fish. Five types of behaviour, ‘basal’, ‘orientation’, ‘positioning’, ‘attack’, and ‘ingestion’, were recognised and are described. Capture of prey small enough to swallow whole was assisted by suction created as the mouth opened to engulf prey. Crustaceans too large to ingest whole were broken into smaller pieces against the substrate. Directional and oscillatory movement were the most effective sensory cues in eliciting feeding behaviour, implicating vision as an important sense for L. unicolor feeding in confined aquaria. Acoustic and olfactory senses are less important in prey capture. The frequency with which spangled perch responded to different sensory cues increased with increasing hunger.
Ultrastructural and cytochemical observations on the granulocytes of the sturgeon, Acipenser brevirostrum (Chondrostei)
Authors: Hine P. M. , Wain J. M.
Published: January 2006

Granulocytes from cranial granulopoietic tissue were studied under the electron microscope, and cytochemistry carried out oncranial and peripheral blood granulocytes of two sturgeons, Acipenser brevirostrum. Ultrastructurally, eosinophils and basophils had homogeneous electron‐dense granules similar to those of teleosts and some higher vertebrates. Neutrophils contained two granule types: small elongated fibrillar granules and large (<3.8μm long) usually homogeneous granules.

Neutrophil fibrillar granules were positive for alkaline phosphatase (ALP), acid phosphatase (ACP), α‐naphthyl acetate esterase (ANAE), acetyl‐l‐tyrosine‐α‐naphthyl esterase (ATNE) and periodic acid Schiff (PAS) reaction. The large homogeneous granules were negative for all enzymes, and were only PAS positive. Eosinophils had granular, cyanide‐, azide‐ and aminotriazole‐resistant peroxidase (PO) and were ACP, ATNE, tosyl‐l‐lysine‐α‐naphthyl esterase (TLNE) and Luxol fast blue positive.

Ultrastructure and cytochemistry are discussed in relation to other vertebrates, and eosinophils identified as the main phagocytic leucocyte.
Observations on the granulocyte peroxidase of teleosts: a phylogenetic perspective
Authors: Mine P. M. , Wain J. M.
Published: January 2006

Observations on granulocyte peroxidase of 123 teleosts are reported and correlated with previous studies to put occurrence of fish granulocyte peroxidase in a phylogenetic perspective. Eosinophil peroxidase occurs in archaic groups such as lungfish and sturgeons, but is usually weak and infrequently observed in chondrichthyans, and in teleosts occurs in some elopomorphs, is consistently observed in stomiiforms, is rarely observed and usually weak in acanthopterygians and absent from salmoniforms, scopelomorphs and paracanthopterygians. Peroxidase is absent from lungfish and sturgeon neutrophils, is present in neutrophils of some elopomorphs and clupeimorphs. both of which are basal teleost groups, but in salmoniforms and higher teleosts is consistently observed in neutrophils. although often weak in pleuronectiforms.

Loss of eosinophil peroxidase and development of neutrophil peroxidase in teleosts may be due to inefficient phagocytosis and loss of peroxidase with degranulation in eosinophils, being superseded by concentration of peroxidase in phagosomes in neutrophils.
Diet of the garfish, Belone belone (L.), from Courtmacsherry Bay, Ireland
Authors: Dorman J. A.
Published: January 2006

Adult garfish were captured by rod and line from Courtmacsherry Bay, Co. Cork, southern Ireland. Examination of gut contents showed that they feed on crustaceans, especially crab larvae, and juvenile fish, mostly clupeids. They also take stranded insects from the sea surface. Post‐larval garfish were found to be feeding on the smaller elements of the neuston, such as copepods and larval bryozoans.
The distribution and dispersal of introduced fish at Thumbi West Island in Lake Malawi, Africa
Authors: Trendall J.
Published: January 2006

The rock‐dwelling cichlids, or mbuna, of Lake Malawi are exceptionally diverse. Explanations of this diversity have used limited dispersal by the mbuna as the basis for allopatric models of speciation. However, there have been no studies that have attempted to define the extent and rates of dispersal of mbuna populations in the field. The present work took advantage of some translocations in which several species of mbuna were introduced to the Cape Maclear region of Lake Malawi from elsewhere in the lake. A detailed series of transects involving observations at four depths was undertaken at Thumbi West Island to define the distribution of the introduced species. There are large differences between species in the extent to which they have spread. Some species are now present all round the island while others have dispersed only a limited distance from the site of the initial introductions. This survey provides the first comprehensive data set on the distribution of the introduced species and it raises a number of important questions regarding their dispersal ability and their likely impact on the endemic community.
The relation between daily rings, body growth and environmental factors in plaice, Pleuronectes platessa L., juvenile otoliths
Authors: Alhossaini M. , Pitcher T. J.
Published: January 2006

The deposition rate of sagittal otolith rings in post‐metamorphosed plaice, Pleuronectes platessa, was considered in relation to body growth under three feeding levels and two photoperiod regimes. Feeding levels and photoperiods significantly influenced the number of rings; more rings were deposited at higher levels of feeding and in longer photoperiod regimes. There was also a linear relationship between fish growth and the number of rings. The results suggest that sagittal rings could be used for aging wild juvenile plaice during the period of the growing season when growth rate is greater than 0.1 mm day1.
Variation in plasma oestrogens and androgens during the seasonal and semilunar spawning cycles of female gulf killifish, Fundulus grandis (Baird and Girard)
Authors: Greeley M. S. , MacGregor R. , Marion K. R.
Published: January 2006

Variations in 17β‐oestradiol, oestrone, testosterone, and 11‐ketotestosterone were measured by radioimmunoassay in the plasma of female Gulf killifish, Fundulus grandis, during their seasonal and semilunar spawning cycles. Both 17β‐oestradiol and testosterone exhibited distinct seasonal variation, peaking very early in the breeding season during March and April, decreasing gradually thereafter the cessation of spawning in late August and the seasonal regression of ovaries in September, and eventually falling below the detectable limits of our assays during the very early stages of seasonal ovarian recrudescence in November. Both steroids also exhibited distinct semilunar variation within the breeding season, with highest plasma concentrations immediately prior to, and during, each spring tide spawning. Such results suggest that these steroids have physiological roles in the generation and regulation of both seasonal and semilunar reproductive cycles: 17β‐oestradiol by controlling development of vitellogenic oocytes; testosterone perhaps by acting as a precursor in the production of oestrogens and other steroids. In contrast, oestrone and 11‐ketotestosterone were only rarely detected, implying that these particular oestrogens and androgens are probably not physiologically active in female killifish.
Aspects of energetics of adult walleye pollock, Theragra chalcogramma (Pallas), from Alaska
Authors: Smith R. L. , Paul A. J. , Paul J. M.
Published: January 2006

Body energy partitioning was examined for field‐caught, adult walleye pollock; additional laboratory studies were conducted on fish held under controlled temperature conditions at Seward, Alaska.

Average consumption for pollock feeding daily was 0.5% of body weight (3100 cal) at 5°C, resulting in an average growth of 0.12% body weight day−1. These results suggest that large pollock grow at similar rates and have similar food conversion efficiencies to those of Atlantic cod held at similar temperatures.

Resting metabolic rates measured on adult fish were combined with similar data from juveniles to calculate a regression of specific metabolic rate against wet weight: y= 173x−026. Maintenance rations amounted to 4.8 cal g−1 day−1 at 5°C, very close to the 0.28% value for juveniles. Estimation of metabolic rate using maintenance ration data resulted in values that were 55% higher than those obtained from oxygen consumption data for unfed fish. Weight loss during starvation was 0.18% of body weight day−1 at 5°C, corresponding roughly to a starvation metabolic rate 50% lower than the resting metabolic rate we report.

We estimate that an adult pollock will lose about 37% of its prespawning body weight and about 46% of its body energy during spawning. These losses result, primarily, from changes in the weight of gonad, liver and somatic tissues as opposed to changes in specific energy content of those tissues.
Changes in ammonia and amino acid levels in the erythrocytes and plasma of carp, Cyprinus carpio, during passage through the gills
Authors: Ogata H. , Murai T.
Published: January 2006

Differences in ammonia and free amino acid levels between the dorsal aorta (post‐gills) and bulbus arteriosus (pre‐gills) were studied in sixteen unanaesthetized carp, Cyprinus carpio, to clarify he roles of erythrocytes in inter‐organ transport of these substances. Both erythrocyte and lasma ammonia concentrations decreased significantly during passage through the gills, and the erythrocyte contribution (53%) to the total net decrease of ammonia on a whole blood basis was approximately equal to that by the plasma (47%). The glutamine level in the plasma showed no significant change, but that in the erythrocytes increased slightly. There were losses of some amino acids from the plasma circulating through the gills, while significant increases were noted in the erythrocytes, i.e., changes in the concentrations of most amino acids were in opposite directions in the erythrocytes and plasma across the gills. The results of this study show that not only plasma but also erythrocytes are involved in ammonia and amino acid transportations in carp.
Cytogenetic studies of Atlantic salmon, Salmo salar L., in Scotland
Authors: Hartley S. E.
Published: January 2006

Chromosome numbers for Atlantic salmon, Salmo salar L., from ten populations in Scotland were ascertained. The majority of fish had 2n = 58, NF = 74 karyotypes, and no polymorphisms between populations were found. The findings suggest that Atlantic salmon in Scotland are cytogenetically homogeneous.
Bioenergetics of growth of a cyprinid, Phoxinus phoxinus (L.): the effect of ration and temperature on growth rate and efficiency
Authors: Cui Y. , Wootton R. J.
Published: January 2006

Growth of minnows, Phoxinus phoxinus, weighing 1‐5.5 g was studied experimentally at five ration levels from starvation to ad libitum and four temperatures ranging from 5 to 15°C. The relationship between specific growth rate (SGR) and ration was a decelerating curve. SGR at maximum rations increased with increased temperature, but at restricted rations it decreased with increased temperature. Predictive models for the specific growth rates were developed using multiple regression. Maintenance rations and optimum rations both increased with increased temperature. Maintenance rations were less sensitive to temperature than optimum rations and mostly lay between 1 and 2% of body weight per day. Conversion efficiencies increased with increased ration from zero value at the maintenance ration to a peak at the optimum ration, then decreased with further increases in ration. At a given restricted ration level, conversion efficiencies generally decreased with increased temperature. At maximum rations, conversion efficiencies were relatively insensitive to temperature. Growth in wet weight, dry weight and energy content showed similar responses to ration, temperature and body weight.
Inhibitory effect of 11‐ketoandrostenedione and androstenedione on spermatogenesis in the three‐spined stickleback, Gasterosteus aculeatus L.
Authors: Andersson E. , Mayer I. , Borg B.
Published: January 2006

Stickleback males were implanted with Silastic capsules filled with 11‐ketoandrostenedione or androstenedione at the end of the breeding season. 11‐Ketoandrostenedione prevented the natural decline in secondary sexual characters and testes weight. It also completely inhibited the commencement of spermatogenesis, which normally takes place in late summer after having been quiescent during the breeding season. Androstenedione also exerted these effects, but to a lesser degree.
The cryopreservation of fish thymocytes and its potential application for immunological reconstitution experiments
Authors: Tatner M. F.
Published: January 2006

Fish thymocytes were cryopreserved by two methods, a programmed freezing method by a direct control system and a mechanical freezing method. There was no loss of viability or ability to respond to Concanavalin A compared to control thymocytes, up to 5 months after cryopreservation, and no difference between the two methods.
Epidermis thickness and secondary sexual characters in mature male and immature Baltic salmon, Salmo salar L., parr: seasonal variations and effects of castration and androgen treatment
Authors: Rydevik M.
Published: January 2006

At the breeding season (November) the mature male parr had a thicker epidermis than had the immature parr. In winter (February) there was no difference, while in May, at the smoltification period, the previously mature male parr had a thicker epidermis than the immature parr. In both categories of fish the epidermis was thinner in May than in November. The epidermal thickness in castrated male parr was the same as in immature parr. Treatment with 11‐ketoandrostenedione (llkΔ4) increased epidermal thickness in castrated males. Treatment with testosterone and llkΔ4 increased epidermal thickness in previously mature males in spring. There was no development of anadromous secondary sexual characters (hooked lower jaw, adult nuptial colouration) in any male.
Episodic events and estuaries: effects of cyclonic flushing on the benthic fauna and diet of Solea bleekeri (Teleostei) in Lake St Lucia on the south‐eastern coast of Africa
Authors: Cyrus D. P.
Published: January 2006

The effects of an episodic event, involving the cyclonic flushing of, and associated rapid decrease in salinity in an estuarine system, on two faunal components was investigated. The rapid salinity decrease of some 25% had a direct, short‐term effect on most components of the benthos of Lake St Lucia, as well as a long‐term effect on the bivalves, particularly Solon cylindraceus, which species was unable to re‐establish itself at previous densities. Indirect long‐term effects were noted in the diet of Solea bleekeri, which feeds predominantly on the siphon tips of S. cylindraceus, in that it switched to feeding on whatever prey it could locate at the surface of the benthos. Although no change in densities of S. bleekeri was noted after the event, it is considered that the resultant change of diet did lead to some stress in the population. This study clearly demonstrates the need to monitor episodic events due to the direct and indirect effects, either short‐ or long‐term, which they may have on the estuarine fauna.
Pre‐adaptive plasticity in atherinids and the estuarine seat of teleost evolution
Authors: Bamber R. N. , Henderson P. A.
Published: January 2006

With the aid of models and selected examples, an analysis of speciation within the family Atherinidae is presented. This is a large family of pelagic fish, many members of which look strikingly similar. They are primarily a marine coastal group, favouring sheltered estuaries and lagoons, although in some regions they have invaded fresh waters.

Many atherinids show a high degree of intraspecific morphological variability which can be linked to their estuarine habitat. It is argued that estuarine and lagoonal environments are physically highly variable and this has acted to select for generalist genotypes able to adjust their morphology, physiology and behaviour to a wide range of conditions. Such plasticity pre‐adapts atherinids to invade and rapidly speciate in fresh waters containing vacant niches. Examples of such invasions and speciation are presented, and the rate of evolution discussed.

The selective forces acting on atherinids should be common to other fish groups, suggesting that many freshwater fish may have estuarine ancestors. The influence of estuaries in evolution may be out of all proportion to their size.
Population dynamics and community structure of fish in the mangroves of Pagbilao, Philippines
Authors: Pinto L.
Published: January 2006

128 fish species were recorded for the mangroves of Pagbilao. Aspects of the population dynamics of the common species, Ambassis kopsi, Secutor ruconius. Leiognathus brevirostris and Prosopodasys gogorzae were investigated. Growth coefficients varied from 0.41 to 1.2. Mortality in the mangroves was high, and most species there breed once per year.

Species diversity (H') of the community ranged from 1.05 to 2.9. It was influenced by evenness rather than by species richness. Species abundance gave a log normal distribution, except during the typhoon, when it fitted the niche preemption model.
A review of information relating to fish passage through turbines: implications to tidal power schemes
Authors: Davies J. K.
Published: January 2006

Field and laboratory studies on the passage of adult and juvenile fish through hydroelectric turbines are reviewed, with special emphasis on tidal schemes in operation. Although the types of injury which fish incur and their frequency are well documented, little appears to be known about the specific hydraulic conditions within the turbine structure which actually cause the injury, despite the fact that the four main causes of fish loss (abrupt changes in pressure, water turbulence, shearing currents and mechanical contact with turbine blades) have been identified.

Factors causing fish mortality fall into two main categories: (a) hydraulic conditions of pressure change, cavitation, shearing and turbulence, producing direct, characteristic injuries; (b) conditions influencing the likelihood of actual fish collision with turbine components. These factors can be enhanced or reduced by alterations in turbine operation and, possibly, design.

The significance of fish behaviour and ecology with respect to prediction of numbers of fish passing through installations, plus criteria which govern actual mortality rates have yet to be elucidated.
Reproductive mode in the percomorph fish genus Polyprion Oken
Authors: Roberts C. D.
Published: January 2006

Reproductive mode of the two widespread species Polyprion americanus (Bloch and Schneider, 1801) and P. oxygeneios (Schneider in Bloch and Schneider, 1801) was investigated in specimens from New Zealand waters. Analysis of sex ratios, length frequencies and gonad morphology indicates that both species are primary gonochorists. Published suggestions that Polyprion species are hermaphroditic and undergo sex change are rejected.
Sexual differences in the increase of white muscle fibres in Argentine hake, Merluccius hubbsi, from the San Matias Gulf (Argentina)
Authors: Calvo J.
Published: January 2006

Growth dynamics of white fibres from axial muscle has been investigated in Argentine hake, Merluccius hubbsi, discriminating between sexes for the first time. The frequency distributions of fibre diameters are remarkably different in both sexes at sizes between 42 and 63·9 cm total length (T.l.). Males have a much lower proportion of newly recruited fibres (0–10 μm) than females; at 52–53·9 cm T.l., females have 4% of fibres in that category and males 0·5%. It appears that, from this size interval onwards, the increase in muscle mass is due only to the increase in diameter of individual fibres, which may exceed 300 μm. The lower recruitment rate of new fibres in males, and its relationship to lower growth rates and smaller final sizes, are discussed, and possible effects of reproductive activity are considered.
The attachment of micro‐organisms to macrophages isolated from the tilapia Oreochromis spilurus Gunther*
Authors: Saggers B. A. , Gould M. L.
Published: January 2006

The non‐specific and specific recognition of Candida guillerimondii and Staphylococcus epidermidis by macrophages isolated from the gills, kidney and spleen of Oreochromis spilurus has been investigated. Lectin‐like receptors that bind L‐fucose, D‐galactose, D‐glucose, D‐mannose, a‐methyl mannoside and N‐acetyl‐D‐glucosamine that are involved in non‐specific recognition have been demonstrated on macrophages isolated from the different organs. In addition, receptors that recognize complement have been shown to function in the recognition of opsonized micro‐organisms.
The effect of calcium concentration on the toxicity of copper, lead and zinc to yolk‐sac fry of brown trout, Salmo trutta L., in soft, acid water
Authors: Sayer M. D. J. , Reader J. P. , Morris R.
Published: January 2006

Yolk‐sac fry of brown trout were exposed to three levels of single trace metals (Cu, 20,40,80 nmol 1‐1; Pb, 12·5,25,50 nmol 1‐1; Zn, 75,150,300 nmol 1‐1) typical of concentrations reported for acid soft waters, in flowing, artificial, soft water media maintained at pH 4·5 and [Ca] of 20 or 200 μmol 1‐1for 30 days.

Mortalities were high in fry subjected to all levels of the three trace metals at [Ca] 20 μmol 1‐1, with 80% of the total deaths occurring between days 11 and 15 of the experiment. 25% mortality occurred at low [Ca] and pH 4·5 in the absence of trace metals, with only one death recorded at [Ca] 200 μmol1‐1’(Cu, 80 nmol 1‐1). At high [Ca] all three levels of Cu and Pb impaired net Na and K uptake; Cu was the only metal to reduce the uptake of Ca. The Zn treatments had no significant effect on mineral uptake. Calcification of centra was reduced by all three Cu treatments at [Ca] 200 μmol 1‐1. The lowest Zn concentration (75 nmol 1‐1) was the only other treatment to impair skeletal development. In the absence of trace metals, low [Ca] significantly reduced Ca, Na and K uptake, skeletal calcification and dry mass at pH 4·5.

The deleterious effects of low Cu, Pb and Zn concentrations at low pH and low [Ca], and the ameliorative effect of higher ambient [Ca], are discussed in relation to fishery status in soft, acid waters.
Cytotoxic reactions of rainbow trout, Salmo gairdneri Richardson, macrophages for larvae of the eye fluke Diplostomum spathaceum (Digenea)
Authors: Whyte S. K. , Chappell L. H. , Secombes C. J.
Published: January 2006

The killing ability of rainbrow trout macrophages for the infective larval stages of Diploslomum spathaceum, cercariae and diplostomules, was investigated. Isolated macrophages kill significant numbers of diplostomules at effector: target ratios of 150: 1 or greater. In vitro killing was not increased using antiserum‐coated larvae or in vivo‐activated macrophages individually, but when they were combined increased killed occurred. Diplostomules were capable of eliciting respiratory burst activity from macrophages in vitro, suggesting that reactive oxygen species may have a role to play in the killing mechanism. The importance of macrophage activation in the protection afforded by immunization against this parasite is discussed.
The effects of prey relative abundance and chemical cues on prey selection in rainbow trout
Authors: Bres M.
Published: January 2006

An optimal foraging model was used to predict prey selection based on both energy maximization and number maximization strategies. The influence of chemical cues and relative abundance on rainbow trout diet selection was examined under laboratory conditions.

In most fish, diet composition was strongly influenced by chemical cues. No fish followed an energy maximization strategy, and selection of prey based on taste persisted despite large caloric penalties associated with these choices. In the absence of chemical cues, diet composition was based on relative abundance of prey (a number maximization strategy). Within the feasible constraints of the optimal foraging model lie a large number of possible diet combinations which would provide sufficient energy for growth and reproduction. This provides a wide scope for feeding flexibility. Response to prey chemical cues may be the basis for observations of individual diet variability in trout.
Mediterranean juvenile bluefin tuna: life history patterns
Authors: Radtke R. L. , Morales‐Nin B.
Published: January 2006

As there is a lack of information on the growth and migrations of bluefin tuna, information about them was gathered using the structural and chemical characteristics of their otoliths and mercury levels in body tissues as indicators of physiological and habitat characteristics. The otoliths of juvenile tuna caught in the Spanish Mediterranean littoral were studied. Otolith increments, assumed to be formed daily, were enumerated. Measurements by wavelength dispersive electron microprobe confirmed the presence of strontium in otolith tissue, and an inverse relationship between strontium/calcium (Sr/Ca) concentration ratio and temperature is suggested. Electron microprobe analyses combined with daily increment analyses of otoliths provided life history profiles for individual fish. Additional Sr/Ca concentration ratio data on fish supported the idea that Sr/Ca ratios can provide information on the environmental history of individual fish. Body concentrations of mercury were related to otolith analyses to suggest age structure, critical life history periods, growth environment, stock structure, food web position, and migration history. The techniques applied present an innovative approach to management‐related problems, and the combination of chemical analyses with structural analyses promises to expand our knowledge of the life history of migratory fishes.
The growth of juvenile Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in a Scottish river system subject to cooling‐water discharge
Authors: Morrison B. R. S.
Published: January 2006

The River Fiddich, a tributary of the R. Spey in north‐east Scotland, is a spawning river for both Atlantic salmon and brown trout. Warm cooling water effluent is discharged from several distilleries at different points in the lower reaches and raises the temperature of the river 1–3°C above ambient for most of the year. Salmon and trout grow more rapidly in this region than further upstream, and juvenile salmon generally migrate a year earlier, as 2 + smolts. Available data were too few to determine whether there was a similar difference for trout. Similar studies on the R. Dullan, a tributary of the Fiddich, and on the Cromdale Burn in the same area, confirmed that the growth rate of fish is faster downstream from distillery discharge points. It is suggested that increased invertebrate production may influence the growth rate.
Analysis of the enzyme polymorphism in a plaice, Pleuronectes platessa L., population from the north‐west coast of Brittany, France
Authors: Brulé T.
Published: January 2006

A study of enzyme polymorphism by electrophoretical techniques permitted the genetic structure and the homogeneity degree of the plaice population present in the Abers Wrac'h and Benoit along the north‐west coast of Brittany to be determined. Thirteen enzymic systems encoded by 21 loci were analysed and nine of these loci were polymorphic at the 5% level. The comparison of allelic frequencies and of observed heterozygosity hobs did not show significant differences between these two individual groups. Nei's genetic identity (I= 0.998) and distance (D= 0.002) as estimated from allelic frequencies showed that the plaice of the two estuaries are very similar.

Thus, the plaice of A. Wrac'h and of A. Benoit belong to the same population in which the average level of polymorphism per locus P is 47% and the observed average heterozygosity per individual Hobs is 0.163 ± 0.094.
Mitochondrial DNA as a genetic marker for brown trout, Salmo trutta L., populations
Authors: Hynes R. A. , Duke E. J. , Joyce P.
Published: January 2006

Mitochondrial DNA was examined in natural and hatchery‐reared stocks of brown trout, using different methods of restriction analysis. The methods included the development of a brown trout mt DNA hybridization probe through cloning part of the brown trout mitochondrial genome. In addition, fragments were analysed by ethidium bromide staining and end‐labelling. The relative merits of each of these methods in assessing levels of genetic relatedness between the natural and hatchery‐reared brown trout stocks were evaluated. In addition, the study revealed a diagnostic mtDNA restriction pattern which could be used as a genetic marker for the discrimination of these two groups of brown trout.
Grouping fails to affect the growth and energy budget of a cyprinid, Phoxinus phoxinus (L.)
Authors: Cui Y. , Wootton† R. J.
Published: January 2006

The effects of grouping on the growth and some components of the energy budget of the minnow, Phoxinus phoxinus (L.), were tested in the laboratory. No effects of grouping were detected on absorption efficiency, the proportion of food energy lost in nitrogenous excretion, maximum rate of food consumption and conversion efficiency. Grouping had no significant effect on either specific growth rate or the dry matter content of individual fish.
Karyotype variability in successive generations after hybridization between the great sturgeon, Huso huso (L.), and the sterlet, Acipenser ruthenus L.
Authors: Arefjev V. A.
Published: January 2006

The karyotypes of bester (the hybrid between great sturgeon and sterlet) in three generations do not differ in diploid chromosome number from parental species and are displaced towards the sterlet in numbers of bi‐ and uni‐armed chromosomes and chromosome arms. The variability of quantitative karyotypic parameters other than number of bi‐armed chromosomes increases considerably (double, on average) in F1 and F2 and declines to the level characteristic of the parental species in F3. The variability results mainly from aneuploidy in microchromosomes and the karyotypic variabilities of 3 to 6‐week‐old and 4 to 5‐month‐old fish are the same. The stabilization of the hybrid karyotype in the third generation is rather rapid and may reflect the formation of a breed. The degree of individual karyotypic variability estimated on the basis of the coefficient of variation is 2‐3 % for parameters other than the number of microchromosomes, for which it is 6‐7%.
Light and scanning electron microscopic studies on the effect of biocidal plant sap on the gills of a hill stream fish, Garra lamta (Ham.)
Authors: Ojha J. , Rooj N. C. , Mittal A. K. , Datta Munshi J. S.
Published: January 2006

The effect of a biocidal plant sap (Terminalia tomentosa) on the gills of a swift‐current‐adapted hill‐stream fish, Garra lamia, has been investigated using light and scanning electron microscopy. The biocidal plant sap affected the dissociation of the gill filament and lamellar epithelia to expose their microvasculature. Some findings on the microvasculature are discussed in the light of their probable functions. Fusion of lamellae and prominent chloride cells are further effects of the plant sap, and their impact on respiratory and osmoregulatory functions of the fish are discussed.

Use of biocidal plant sap in mass killing of hill‐stream fish is considered in relation to conservation.
Seasonal dynamics of the acanthocephalan Pomphorhynchm laevis (Müller, 1776) in its intermediate and preferred definitive hosts
Authors: Brown A. F.
Published: January 2006

No seasonal cycle was found in either the prevalence or the intensity of natural Pomphorhynchus laevis infections in Leuciscus cephalus. There was a slight seasonal change in female maturity distribution but only irregular fluctuations in the size structure of the adult parasite population throughout the year. Cystacanths were available in all seasons. Rates of parasite growth, maturation and mortality, but not establishment, increased with water temperature (or factors indirectly associated with elevated water temperature) in laboratory‐infected Salmo gairdneri. Increased rates of parasite growth and maturation mask any marked shifts in the size and maturity structure of the adult parasite population which might otherwise be due to the higher turnover of adult parasites in the summer months.
The spawning activity of cod, Gadus morhua L.
Authors: Kjesbu O. S.
Published: January 2006

Aspects of the reproduction of reared cod, Gadus morhua L., with special emphasis on the females, were studied under laboratory conditions. The fecundity and condition factor were 2–5 and 1–5 times, respectively, that of wild cod. A total of 18 spawning females were kept in separate tanks/ chambers, each with one or two males. Seven of the 18 females were classified as stressed, based upon behaviour, irregular spawning intervals and low fertilization rates of the eggs. The reared cod were found to spawn 17–19 batches. The number of eggs liberated in each batch normally followed a smooth, dome‐shaped curve with time. The fertilization rate was normally 100%. Egg size decreased from first to last batch and the egg dry weight decreased by about 20–30%. The reared cod showed the same egg diameter to dry weight relation as wild cod. Egg diameter of first batch and maternal fish length were significantly positively correlated. The mean spawning interval for the female and the mean water temperature during its spawning were negatively correlated. The reared cod spawned in both the night and the day for about 50–60 days.
Changes in the sexual tendency accompanying selection for aggressiveness in the three‐spined stickleback, Gasterosteus aculeatus L.*
Authors: BAKKER Th. C. M. , SEVENSTER P.
Published: January 2006

Independent selection experiments for reduced juvenile and reduced territorial aggression levels in male three‐spined sticklebacks both resulted in reduced courtship aggression levels. In the low juvenile aggression line this is accompanied by an enhanced sexual activity, but in the low territorial aggression line males display a reduced sexual activity. These results are consistent with a mutually inhibitory relationship between the aggressive and sexual tendencies, if selection for juvenile aggressiveness has only affected the aggressive tendency while selection for territorial aggressiveness has simultaneously affected the aggressive and sexual tendencies in the same direction. This is in agreement with the hormonal changes (pituitary‐gonadal axis) suggested by the selection studies.
Laboratory and field studies on diet choice in three‐spined sticklebacks, Gasterosteus aculeatus L., in relation to profitability and visual features of prey
Authors: Ibrahim A. A. , Huntingford F. A.
Published: January 2006

Diet choice by three‐spined sticklebacks was investigated under both laboratory and field conditions. In the laboratory, sticklebacks did not always choose the more profitable of two prey items; instead, they apparently selected prey according to a set of proximate decision rules based on visual cues provided by the prey. Studies of the diet of sticklebacks in the field suggest that they may use the same set of proximate decision rules to select their food and that in these more complex conditions this may lead them to feed preferentially on the more profitable types of prey. In general, sticklebacks selected zooplanktonic rather than benthic prey (which is less profitable), but the importance of benthos in the diet increased as the density of zooplankton decreased.
Pathological changes in the gill filaments of Acanthopagrus australis (family Sparidae) associated with the post‐settlement growth of a lernaeopodid copepod, Alella macrotrachelus
Authors: Roubal F. R.
Published: January 2006

The extent of the histopathology associated with the attachment of post‐settlement stages of the lernaeopodid copepod Alella macrotrachelus on the gills of Acanthopagrus australis was related to parasite size. Initial penetration of the attachment organ into the epithelium was associated with hyperplasia, oedema and accumulation of infiltrating cells in the immediate vicinity of the frontal filament or bulla. Adult parasites caused crypting and fusion of filaments with associated chronic inflammation. Penetration of the bulla into the connective tissue invoked fibroplasia and chondrocyte proliferation that enclosed the bulla. The bulla matured from the centre to the periphery by a condensation of the matrix into coarse fibrils. The bulla was delineated by a tri‐laminar wall from the surrounding connective tissue fibrils.
Gonochorism and seasonal variations in the gonads of the labrid Symphodus (Crenilabrus) ocellatus (Forsskål)
Authors: Bentivegna F. , Benedetto F.
Published: January 2006

A histological study of gonadal organization of 354 Symphodus ocellatus caught in the Bay of Naples from June 1985 to December 1986 demonstrated the absence of sexual inversion in this species. Four phases of gonadal development, related to the seasonal cycle, are described. During the reproductive period the ovaries showed the asynchrony in oocyte development that is typical of serial spawners. The testes of three types of males present in this species (territorial, satellite and sneaker males) were examined: the only difference found was in the gonadal growth pattern during the reproductive period.