bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal structures of apo wild‐type M. jannaschii tyrosyl‐tRNA synthetase (TyrRS) and an engineered TyrRS specific for O‐methyl‐L‐tyrosine
Authors: Zhang Yan , Wang Lei , Schultz Peter G. , Wilson Ian A.
Published: April 2005

The Methanococcus jannaschii tRNATyr/TyrRS pair has been engineered to incorporate unnatural amino acids into proteins in E. coli. To reveal the structural basis for the altered specificity of mutant TyrRS for O‐methyl‐l‐tyrosine (OMeTyr), the crystal structures for the apo wild‐type and mutant M. jannaschii TyrRS were determined at 2.66 and 3.0 Å, respectively, for comparison with the published structure of TyrRS complexed with tRNATyr and substrate tyrosine. A large conformational change was found for the anticodon recognition loop 257–263 of wild‐type TyrRS upon tRNA binding in order to facilitate recognition of G34 of the anticodon loop through π‐stacking and hydrogen bonding interactions. Loop 133–143, which is close to the tRNA acceptor stem‐binding site, also appears to be stabilized by interaction with the tRNATyr. Binding of the substrate tyrosine results in subtle and cooperative movements of the side chains within the tyrosine‐binding pocket. In the OMeTyr‐specific mutant synthetase structure, the signature motif KMSKS loop and acceptor stem‐binding loop 133–143 were surprisingly ordered in the absence of bound ATP and tRNA. The active‐site mutations result in altered hydrogen bonding and steric interactions which favor binding of OMeTyr over l‐tyrosine. The structure of the mutant and wild‐type TyrRS now provide a basis for generating new active‐site libraries to evolve synthetases specific for other unnatural amino acids.
Three‐dimensional structure of (1,4)‐β‐d‐mannan mannanohydrolase from tomato fruit
Authors: Bourgault Richard , Oakley Aaron J. , Bewley J. Derek , Wilce Matthew C.J.
Published: April 2005

The three‐dimensional crystal structure of tomato (Lycopersicon esculentum) β‐mannanase 4a (LeMAN4a) has been determined to 1.5 Å resolution. The enzyme adopts the (β/α)8 fold common to the members of glycohydrolase family GH5. The structure is comparable with those of the homologous Trichoderma reesei and Thermomonospora fusca β‐mannanases: There is a conserved three‐stranded β‐sheet located near the N terminus that stacks against the central β‐barrel at the end opposite the active site. Three noncanonical β‐helices surround the active site. Similar helices are found in T. reesei but not T. fusca β‐mannanase. By analogy with other β‐mannanases, the catalytic acid/base residue is E204 and the nucleophile residue is E318. The active site cleft of L. esculentum β‐mannanase most closely resembles that of the T. reesei isozyme. A model of substrate binding in LeMAN4a is proposed in which the mannosyl residue occupying the −1 subsite of the enzyme adopts the 1S5 skew‐boat conformation.
Tidal and diel timing of river entry by adult Atlantic salmon returning to the Aberdeenshire Dee, Scotland
Authors: Smith I. P. , Smith G. W.
Published: April 2005

The timing of salmon migration from the estuary of the Aberdeenshire Dee into the river in relation to tidal phase and time of day was studied by combined acoustic and radio‐tracking of individual fish and by analysing records of untagged fish from a resistivity fish counter 0.8 km upstream from the tidal limit. Up‐estuary movements that led to river entry were predominantly nocturnal and tended to occur during the ebb tide. Penetration into the non‐tidal reaches of the river also tended to occur at night, but the timing of salmon movements was no longer significantly associated with tidal phase. The tracking data suggested that the reduction in the strength of the association between salmon migration and tidal phase resulted from variability in rates of progress from the estuary to the river. This variability may have been random, or related to changes in migratory behaviour during entry to fresh water. A simulation of upstream progress by groups of salmon illustrated the decay of the relationship between salmon movements and tidal phase and the advance of the average tidal phase of observed salmon movements with increasing distance of the observation point from where movements were initiated. The magnitude of these effects depended on the average rate of upstream progress and variability in the rate of progress, being greatest when upstream progress was slow and variable. These results highlight a limitation of point observations of migration with regard to identifying environmental stimuli for migration and quantifying their effects.
Low fat contents in female silver eels: indications of insufficient energetic stores for migration and gonadal development
Authors: Svedäng H. , Wickström H.
Published: April 2005

The main energetic stores at the silver eel stage were studied by analysing muscle fat concentrations and hepatosomatic indices in female silver eels from various habitats in Sweden. Muscle fat concentrations varied both within and between localities and lean eels with muscle fat concentrations <20% occurred at all study sites. Furthermore, no correlation could be found between muscle fat content and internal or external maturation indices, neither was the relative liver size related to the maturation process, as the correlation between the hepatosomatic and gonadosomatic indices was very weak. Consequently, it was concluded that silvering and the spawning migration may begin also at low muscle fat concentrations. However, most of the energy reserve is stored as muscle fat in eel, and it is highly unlikely that female silver eels with such low fat contents, as were observed occasionally in this study, will ever recruit to the next generation. Therefore, it is suggested that the maturation process in eel is more flexible than previously recognized, and that this process might be temporarily arrested and feeding resumed during the first part of the migratory phase.
The so‐called tonic muscle fibre type in cyprinid axial muscle: their morphology and response to endurance exercise training
Authors: Sänger A. M.
Published: April 2005

The morphology and the effect of an endurance training programme on tonic muscle fibres were studied in chub Leuciscus cephalus, by means of histochemistry and immunohistochemistry, electronmicroscopy and morphometry/stereology. Location and distribution, SDH‐ and mATPase‐activity, reaction to an anti‐tonic myosin antibody and ultrastructural features of the fibre type were investigated. With regard to training conditions, fibre size was not significantly affected. However, an increase in the volume densities of mitochondria, lipid and myofibrils can be observed, suggesting a training influence on the aerobic capacity of the so‐called tonic muscle fibres. Based on the quantitative findings, the fine structure and the response to training, similarities with intermediate muscle fibres and the functional role of these so‐called tonic muscle fibres are discussed.
Regulation of hyperphagia in response to varying energy deficits in overwintering juvenile Atlantic salmon
Authors: Bull C. D. , Metcalfe N. B.
Published: April 2005

Resident juvenile Atlantic salmon responded to a period of winter food restriction by subsequently increasing appetite when food again became available. This hyperphagy contributed to the restoration of an energy deficit (derived from a biometric estimation of body lipid reserves) incurred during the period of food restriction. The extent of this deficit influenced the duration of the hyperphagic response: those fish incurring the greatest fat losses maintained appetite longer than those with a smaller energy deficit. The initial feeding intensity of fish incurring a wide range of fat losses was found to be similar, indicating that fish were regulating the length as opposed to the intensity of the hyperphagic response in order to restore losses. The ecological implications of the results are discussed in relation to juvenile salmon overwintering strategies.
Genetic divergence and interactions in the wild among native, farmed and hybrid Atlantic salmon
Authors: Einum S. , Fleming I. A.
Published: April 2005

There is concern that the progeny resulting from the spawnings of escaped farmed Atlantic salmon may compete with and disrupt native salmon populations. This study compared, both in the hatchery and in the wild, fitness‐related traits and examined interactions among farmed, native and hybrid 0+ parr derived from controlled crosses and reared under common conditions. The farmed salmon were seventh‐generation fish from the principal commercial strain in Norway and native salmon were from the rivers Imsa and Lone, Norway. In the hatchery, farmed salmon were more aggressive than both native populations and tended to dominate them in pairwise contests. Farmed salmon were also more prone to risk, leaving cover sooner after a simulated predator attack, and had higher growth rates than native fish. Interbreeding between farmed and native fish generally resulted in intermediate expression of the above traits. There was, however, evidence of hybrid vigour in Lone/farmed crosses which were able to dominate both pure Lone and farmed parr in pairwise contests. In the wild, observations of habitat use and diet suggested that the populations compete for territory and food, and both farmed fish and hybrids expressed higher growth rates than native fish. Our results suggest that these innate differences in behaviour and growth, that probably are linked closely to fitness, will threaten native populations through competition and disruption of local adaptations.
Foam nest production in the armoured catfish
Authors: Andrade D. V. , Abe A. S.
Published: April 2005

Foam nest production in Hoplosternum littorale is described in detail. This fish produces foam, while swimming belly‐up, by pumping water over the gills and using their pelvic fins to mix water and mucus. The bubbles resulting from this process are added to plant debris carried by the male, which possesses a specialized pectoral fin spine to perform such activity.
Genetic population structure of the catadromous Perciform: Macquaria novemaculeata (Percichthyidae)
Authors: Chenoweth S. F. , Hughes J. M.
Published: April 2005

Genetic population structure in the catadromous Australian bass Macquaria novemaculeata was investigated using samples from four locations spanning 600 km along the eastern Australian coastline. Both allozymes and mtDNA control region sequences were examined. Population subdivision estimates based on allozymes revealed low levels of population structuring (Gst=0·043, P<0·05). However, mtDNA indicated moderate levels of geographic population structure (Gst=0·146, P<0·0l). Phylogenetic analysis of mtDNA control region sequences (mean sequence divergence 1·9%) indicated little phylogeographic structuring. Results suggested that genotypic variation within each river population, while being affected primarily by genetic drift, was also prevented from more significant divergence by homogenizing levels of gene flow—synonymous with a one‐dimensional stepping‐stone model of population structure. The catadromous life history of Macquaria novemaculeata was considered to be influential on the pattern of population structure displayed. Results were compared to the few population genetic studies involving catadromous fishes, indicating that catadromy alone is unlikely to be a good predictor of population structure. A more comprehensive suite of biological characteristics than simple life‐history traits must be considered fully to allow reliable predictive models of population structure to be formulated.
Seasonal cycles in total chemical composition of two Lake Baikal benthic‐pelagic sculpins (Cottocomephorus, Cottoidei)
Authors: Kozlova T. A.
Published: April 2005

Annual cycles in chemical composition of the body, liver, gonads, red and white muscles were determined for two medium fat sculpins, Cottocomephorus grewingki and C. inermis, endemic to Lake Baikal. Their total lipid content ranged from 3 to 9% during the year. The content of defatted dry substance was 14–17%, similar to the protein content of the other Baikalian cottoid fishes. The prespawning period was characterized by a positive lipid and protein balance in both species. In C. grewingki the liver performed largely a metabolic function, whereas in C. inermis it served also as a storage site for lipid reserves. During spawning, total body lipids of females of both species showed a two‐ to threefold decrease. Males of C. grewingki guarding nests deplete greatly their total body lipids, which decrease seven‐ to ninefold by the time of larval hatching in comparison with the prespawning period, and constitute 1–2%. After spawning, lipid reserves of C. grewingki were quickly restored to the initial level (from about 3 to 9%) and maintained during the long sexual maturation period. In C. inermis total body lipids increased only twofold in comparison to those observed during the spawning period.
Waste‐water management plant effluents cause cellular alterations in the skin of brown trout
Authors: Burkhardt‐Holm P. , Escher M. , Meier W.
Published: April 2005

To assess the impact of a sewage plant on fish, brown trout Salmo trutta were kept in two cages for 55 days in a moderately polluted river upstream of a sewage plant. In one of the cages, undiluted treated waste water of the sewage plant (WWE) was added at an average concentration of 5%, whereas the other cage received river water (R) only. A high mortality occurred in the WWE group. In comparison to control trout held in tap water, the skin structure and ultrastructure were altered clearly in both groups exposed to river water, including necrosis, apoptosis, decreased number of mucous cells, decrease in epidermal thickness, invasion of leucocytes, extension of melanocytes into the epidermis, being gradually more prominent in the WWE group. The most obvious difference between the two exposed groups was found in structure, size and electron density of the secretory vesicles of the filament cells. This and the observed vacuolation of Golgi saccules are indicative for disturbances in the secretory pathway of the filament cells. Certain toxins were suspected to cause the decompaction of myelin sheaths demonstrated in both groups. Reasons for the rather minor overall differences between the exposed groups are discussed. The extremely high mortality rate in the WWE group supports the importance of reducing the load of pollutants in the effluent of the waste‐water management plant.
Phenotypic plasticity and predator effects on morphology and physiology of crucian carp in nature and in the laboratory
Authors: Holopainen I. J. , Aho J. , Vornanen M. , Huuskonen H.
Published: April 2005

Crucian carp Carassius carassius show great phenotypic plasticity in individual morphology and physiology, and strong variation in population density in different fish communities. Small fish with shallow bodies and large heads are typical in overcrowded monospecific fish communities in small ponds, whereas deep‐bodied, large fish are found in larger, multispecies lakes. Crucian carp are especially vulnerable to predation by piscivorous fish and their greater relative body depth in multispecies fish communities has been proposed to be an induced defence against size‐limited predation, and hence to be an adaptive feature. Data are presented here on the two divergent body forms in field populations in eastern Finland, together with results of laboratory experiments on predator effects on morphology and physiology (growth, respiration, heart rate). The deep body can be achieved in a few months by introducing a low population density of shallow‐bodied fish into a food‐rich environment with no piscivores. In the laboratory, both the presence of piscivores (chemical cues) and enhanced food availability increased the relative depth of crucian carp, but only to a modest extent when compared to natural variation. It is concluded that the deep‐body form of crucian carp in the low density populations of multispecies fish communities is the normal condition. Reproduction in monospecific ponds results in high intraspecific competition, low growth rate and a stunted morphology. According to pilot tests, the mechanism behind the predator effect in the laboratory might be a behavioural reaction to chemical cues (alarm substances/predator odour) causing changes in energy allocation: predator‐exposed crucian carp adopt a ‘hiding’ mode with decreased activity (less swimming, lower respiration and heart rate) and with higher overall growth. Whether, and to what extent, this predator‐induced mechanism works in nature is unclear.
The effect of physical condition and shoalmate familiarity on proliferation of alarm substance cells in the epidermis of fathead minnows
Authors: Wisenden B. D. , Smith R. J. F.
Published: April 2005

Ostariophysan fishes have specialized epidermal alarm substance cells (ASCs). In this study, metabolic cost to the production and maintenance of these cells was demonstrated. Fathead minnowsPimephales promelaswere maintained on high or low food rations and, to test for the effect of social context on the number of ASCs, they were held with either zero or two shoalmates. Shoalmates were familiar (from the focal fish's shoal), or unfamiliar (from a shoal separated by 1 km from the focal fish's shoal). After 16 days, epidermal thickness, number of mucus cells and number of ASCs were all significantly greater for minnows on the high ration than for those on the low ration. Within the high ration group, physical condition was positively correlated with epidermal thickness and ASC number. The shoalmate treatment had no measurable effect on the epidermis. It was concluded that food availability determines investment into ASCs, inferring a trade‐off between the cost of ASCs and the fitness benefits they accrue.
The distribution and function of mucous cells and their secretions in the alimentary tract of Arrhamphus sclerolepis krefftii
Authors: Tibbetts I. R.
Published: April 2005

The mucosa of the mouth, pharynx, oesophagus and rectum of Arrhamphus sclerolepis krefftii contain saccular mucous cells and the lining of the intestinal mucosa contains goblet mucous cells. Saccular mucous cells in the buccal epithelium are present in relatively low densities and contain acidic and neutral glycoprotein‐secreting cells in an approximately 1:1 ratio. The saccular mucous cells in the mucosa of the pharynx, oesophagus and rectum are abundant and contain acidic glycoprotein which consists principally of sialomucin with traces of sulphomucin distributed around the periphery of the mucous vacuoles. Goblet cells in the intestinal mucosa contain neutral glycoprotein. Mechanically digested plant material within the lumen of the gut is bound by a sheath of acidic glycoprotein which is in contact with the intestinal mucosa. From these observations and with information on the known properties of acidic glycoproteins, a novel mechanism for the involvement of mucus in the extraction of nutrients from plant material mechanically digested by fish is proposed.
Characterization of parvalbumin isotypes in white muscle from the barbel and expression during development
Authors: Huriaux F. , Collin S. , Vandewalle P. , Philippart J. C. , Focant B.
Published: April 2005

Parvalbumin isotypes PA II, PA III, PA IVa, and PA IVb were isolated by chromatography from trunk white muscle of barbel and physicochemically characterized. Electrospray ionization mass spectroscopy revealed that PA II has a lower molecular weight than the other isotypes and that PA IVa and PA IVb each consist of two subforms. Isotype distribution was studied by polyacrylamide gel electrophoresis. In adult fish, the total parvalbumin titre decreased and the isotype distribution varied from the anterior to the posterior myotomes. In the course of barbel development, the total parvalbumin titre increased rapidly as fish standard length increased from 1·3 to 5 cm; then sloped down gently as the length increased to 60 cm. At least six parvalbumin isotypes were identified, three of which are different forms (a, b, and c) of PA II. These three forms were present together at the larval stage, but PA IIc and chiefly PA IIb appeared as early isotypes, contrary to PA IIa which was present until the adult period. Later PA IVb accounted for up to 90% of the total parvalbumin content; PA III and PA IVa are minor adult isotypes. Temporal and spatial variations in the total parvalbumin titre and in the differential expression of barbel parvalbumin isotypes very likely reflected the functional requirements of the fish axial musculature according to fish size and myotome location. Physiologically, the larval isotypes could promote faster relaxation of fast fibres than the adult isotypes, and hence favour shorter contraction times.
Variations in feed intake and growth of Baltic salmon and brown trout exposed to continuous light at constant low temperatures
Authors: Koskela J. , Pirhonen J. , Jobling M.
Published: April 2005

Interindividual variations in feed intake and growth were studied in Baltic salmon Salmo salar and brown trout S. trutta, held under constant low temperatures of 2, 4 or 6° C and continuous light for 2 months. Rates of feed intake and growth were dependent upon rearing temperature, being lowest at 2° C and highest at 6° C. Further, feed intake and growth were initially low, but increased during the course of the experiment in both species and at all temperatures. These results suggest that acclimatization to the rearing conditions may have required several weeks. The increase in group mean feed intake with time was the result of both an increase in the proportions of fish that fed and an increase in feed intake amongst feeding fish. At the same time as feeding and growth rates increased, interindividual variations in feed intake and growth tended to decrease, suggesting that individual fish were acclimatizing to the new rearing conditions at different rates. Thus, the differences in group mean feed intake and growth rates observed at a given temperature reflected interindividual variations among fish making up the groups. This suggests that group rates of feed intake and growth are not only temperature‐ dependent, but that they are also highly influenced by variability among fish making up the group.
Shifts in morphometrics and their relation to hydrodynamic potential and habitat use during grayling ontogenesis
Authors: Sagnes P. , Gaudin P. , Statzner B.
Published: April 2005

The theory of saltatory ontogeny predicts sudden morphological shifts during fish development which often occur simultaneously with physiological, anatomical or behavioural shifts. Therefore, our objectives were to identify potential sudden morphological shifts during grayling Thymallus thymallus ontogenesis and to check if these shifts affected the hydrodynamic potential of grayling in periods of known shifts in habitat use. In the 144 grayling studied (total length: 14·9–142·7 mm), three of 28 morphological variables considered revealed saltatory events during ontogenesis: position of maximal body height, position of maximal body width, and length to pelvic fin insertion. Using all variables (except total and standard length), five morphological groups were separated by multivariate analysis and each group had a particular hydrodynamic potential related to the drag of flow. Between these five different morphological groups, differences in the physical habitat use were observed. Basically, the saltatory pattern during grayling ontogenesis corresponded to a sequential habitat use that increased flow exposure and, simultaneously, to a stepwise improvement (at each habitat shift) of the hydrodynamic potential until the body had a shape that minimized drag of flow. The study confirms the theory of saltatory ontogeny for grayling in a context of flow physics and hydrodynamic adaptations.
State‐dependent feed acquisition among two strains of hatchery‐reared Arctic charr
Authors: Damsgård B. , Arnesen A. M. , Baardvik B. M. , Jobling M.
Published: April 2005

The effects of genetic and environmental factors on aggression and feeding hierarchies were studied using X‐radiography to measure food intake by hatchery‐reared individuals of two strains (Hammerfest and Svalbard) of Arctic charr Salvelinus alpinus. A reduction in food rations and/or water current speed increased intraspecific aggression, and both factors led to increased interindividual variability in food intake, increasing the coefficient of variation (CV). Following a return to pre‐manipulation conditions, CVs decreased to their original level. In control groups, CVs and share of group meals were stable throughout the experiment. The increase in CVs following manipulation was the result of a small number of dominant individuals obtaining a high share of the meal. Restriction in food ration affected share of meals, specific growth rates and the frequencies of non‐feeding fish, while reductions in water current speed affected only share of meals. Feeding hierarchies were size‐dependent in the control groups. In contrast, no relationships between body weight and feeding rank were evident in groups in which food ration or water current speed were reduced. A small, but consistent, difference was revealed in feeding hierarchy responses between the two strains.
The response of bleak to predator odour of unfed and recently fed pike
Authors: Jachner A.
Published: April 2005

Feeding and growth responses of bleak Alburnus alburnus to the odour of unfed and recently fed pike Esox lucius were quantified in laboratory experiments. Bleak reacted more strongly to the latter than to the former and feeding rates were lowered by 35 and 20%, respectively. The decreases in feeding rates were not an effect of the absence of fish from the feeding place, but of a lowered feeding efficiency due mainly to diminished time spent foraging. The lowered consumption rate of bleak exposed to the odour of recently fed pike caused a decrease in their individual growth rate. The stronger reaction to the recently fed pike stimulus supports the view that alarm substance is a marker for predator odour. In the absence of any further signal from the predator, the bleak became habituated to the predator odour and showed the reaction for only 5 days.
Sexual differentiation in Salaria (=Blennius) pavo
Authors: Patzner R. A. , Kaurin G.
Published: April 2005

The sexual differentiation of Salaria (=Blennius) pavo is described from the stage of hatching to a body length of 35 mm. At hatching, the primordial germ cells (PGCs) can be recognized clearly. At a standard body length of 5 mm, they begin to protrude into the peritoneal cavity and at 14 mm they transform to oogonia. At 17 mm length, the first oocytes can be observed. In males at a standard length of 16–17 mm, the first signs of a differentiation into a testis can be recognized. Shortly after the differentiation of the male sex, the division of the male gonad into a testis and a testicular gland can be seen. The fine structural characteristics of the PGCs and of differentiation stages are presented.
Potential artefacts in morphometric analyses of fish: effects of formalin preservation on 0+ grayling
Authors: Sagnes P.
Published: April 2005

In 0+ grayling, 2 months of preservation in a 4% formalin solution usually caused decreases in various body lengths and fin areas and increases in various body widths. These effects of formalin were variable between two grayling populations and among three length classes of one population.
Ichthyophonus infections in cultured marine fish from Spain
Authors: Franco‐Sierra A. , Sitj́a‐Bobadilla A. , Alvarez‐Pellitero P.
Published: April 2005

Ichthyophonus sp. is reported for the first time in Mugil capito (thinlip grey mullet) and Li a saliens (leaping grey mullet). The fungus was also found in L. aurata (golden grey mullet), Dicentrarchus labrax (sea bass), Sparus aurata (gilthead sea bream) and Scophthalmus maximus (turbot), whereas Mugil cephalus (grey mullet) was not parasitized. In fish sampled periodically, the highest prevalences were observed in sea bass and the lowest in turbot. Among the fish sampled occasionally, the fungus was found associated to an epizootic in thinlip grey mullet. Ichthyophonus was never found in fish weighing <0·5 g. An increase in the prevalence of infection with the age of turbot and gilthead sea bream was observed. Gilthead sea bream and sea bass showed higher prevalences in a closed system than in open and semi‐intensive systems. Multinucleate spherical spores, hyphae and endospores of Ichthyophonus sp. parasitized different organs of thinlip and leaping grey mullets, though infection intensity was maximal in the spleen. In the remaining fish, the fungus was found mainly in the trunk kidney, where it appeared frequently in a necrotic form. Ichthyophonus sp. can be considered a potential threat for marine fish aquaculture, especially in culture conditions which may favour the introduction and transmission of the fungus.
Seasonal cycles of gonadal development and plasma sex steroid levels in Epinephelus morio, a protogynous grouper in the eastern Gulf of Mexico
Authors: Johnson K. , Thomas P. , Wilson R. R.
Published: April 2005

In a field population of the protogynous red grouper Epinephelus morio in the eastern Gulf of Mexico, females with oocytes at all stages of development were collected during the spawning season suggesting that several batches of oocytes may be released over the spawning period. Plasma oestradiol (E2) levels were highest in ripe females whose gonads contained both cortical alveoli and vitellogenic oocytes during the breeding season. Males were still spermiating as late as August, although levels of androgens 11‐ketotestosterone (11‐KT) and testosterone (T) had declined from their peaks in March. A few red grouper with either perinucleolar or cortical alveoli stage oocytes were undergoing sex change both during and after the spawning period. Low levels of E2, T and 11‐KT were detected in transitionals. Proliferation of male tissue was not restricted to any specific area of the gonad but occurred in pockets within the ovarian lumen. The sequence of an increase in gonial cells along the periphery of the lamellae, increase in interstitial tissue, degradation of female elements, and formation of a sperm duct seemed to be concurrent with spermatocyte proliferation and the process of preparing the gonad to function as a testis.
Use of shallow marginal habitat by Phoxinus phoxinus: a trade‐off between temperature and food?
Authors: Garner P. , Clough S. , Griffiths S. W. , Deans D. , Ibbotson A.
Published: April 2005

Fish may alter their habitat use in accordance with the profitability of differing habitat patches. During summer, in the River Frome, minnows Phoxinus phoxinus used shallows in a selective manner, preferring shallows in which water temperature was higher than the ambient river temperature. During the morning and evening, the minnows occasionally entered the shallows but did not linger. They spent considerably longer periods in the shallows when water temperature was greater than in the main channel of the river. During these periods the minnows were inactive. Gut fullness of wild minnows varied temporally and on one occasion spatially, with gut fullness rising rapidly after dawn and remaining high throughout the day. Minnows held in enclosures in the river had significantly higher gut fullness than those held in the shallows. The minnows use shallows that are warmer than the adjacent river preferentially but must return to the river to feed. Thus, there is evidence for a trade‐off between a habitat with high prey density, but low temperature and a low prey density, warmer habitat.
Long‐term study of the ecology of wild Atlantic salmon smolts in a small Norwegian river
Authors: Jonsson N. , Jonsson B. , Hansen L. P.
Published: April 2005

Backcalculated lengths at the end of the first growth season in wild Atlantic salmon Salmo salar differed significantly between parr smolting at age 1, 2 and 3 years over a period of 11 years (i.e. 1983–1993). Mean body lengths of the respective age groups at the end of the first growth period were 11·1, 6·2 and 4·7 cm, respectively. The mean percentage distribution of fish smolting at age 1, 2 and 3 was 14, 78 and 7%, and the mean smolt age was 1·95 years. Mean lengths at smolting of age groups 1, 2 and 3 were 13·6, 15·8 and 17·5 cm, respectively. Females outnumbered males among the downstream migrating smolts with a mean sex ratio (females/ males) estimated at 1·61, with a significant female surplus in 7 of the 11 years sampled. Of the smolts sampled, 14% exhibited enlarged gonads indicative of parr maturation, and all were males (37% of the parr males sampled). Mean annual smolt density from 1975 to 1996 was 13·4 individuals 100 m−2 ranging between 0·3–31 smolts 100 m−2. Mean densities (100 m−2) of the smolts aged 1, 2 and 3 years were 1·5, 9·3 and 0·9 fish, respectively. Mean annual biomass for the 22‐year period (1975–1996) was estimated at 437 g 100 m−2, with a range of variation from 136 to 683 g 100 m−2. Smolt age 2 made up 81% of the mean annual biomass (355 g 100 m−2) and smolt age 1 and 3, 8% (35 g 100 m−2) and 11% (47 g 100 m−2), respectively.
Movements of adult Atlantic salmon through a reservoir above a hydroelectric dam: Loch Faskally
Authors: Gowans A. R. D. , Armstrong J. D. , Priede I. G.
Published: April 2005

Movements of adult Atlantic salmon were determined as they migrated through Loch Faskally, a 4‐km long hydroelectric reservoir in North‐east Scotland. The horizontal and vertical movements of four salmon were monitored for periods of 4–7 days using depth‐sensing acoustic transmitters in June–July 1995. Each fish began sustained directed upstream movements within 5·5 h after release at swimming speeds of 0·15–0·40 bl s−1. Three fish reached the head of the loch after 7·25–17 h, but then returned downstream. The four fish remained in the upper half of the loch for 15–51 days, making localized movements. Mean depths of fish were 3·7–4·0 m (max 20·7 m). Two fish were recorded at significantly shallower depths at night than during the day. Departure from the loch coincided with periods of high water flow into the reservoir. In May–July 1996, 17 radio‐tagged salmon entered Loch Faskally and reached the head of the loch in 3 h–5·8 days (mean 39 h). The durations of stay in the loch varied from 3 h 50 min to 67·4 days (mean 10·9 days). Only two radio‐tagged salmon left the loch under conditions of high water flow into the loch.
Stock structure of Lake Baikal omul as determined by whole‐body morphology
Authors: Bronte C. R. , Fleischer G. W. , Maistrenko S. G. , Pronin N. M.
Published: April 2005

In Lake Baikal, three morphotypes of omul Coregonus autumnalis migratorius are recognized; the littoral, pelagic, and deep‐water forms. Morphotype assignment is difficult, and similar to that encountered in pelagic and deep‐water coregonines in the Laurentian Great Lakes. Principal component analysis revealed separation of all three morphotypes based on caudal peduncle length and depth, length and depth of the body between the dorsal and anal fin, and distance between the pectoral and the pelvic fins. Strong negative loadings were associated with head measurements. Omul of the same morphotype captured at different locations were classified to location of capture using step‐wise discriminant function analysis. Jackknife correct classifications ranged from 43 to 78% for littoral omul from five locations, and 45–86% for pelagic omul from four locations. Patterns of location misclassification of littoral omul suggested that the sub‐population structure, hence stock affinity, may be influenced by movements and intermixing of individuals among areas that are joined bathymetrically. Pelagic omul were more distinguishable by site and may support a previous hypothesis of a spawning‐based rather than a foraging‐based sub‐population structure. Omul morphotypes may reflect adaptations to both ecological and local environmental conditions, and may have a genetic basis.
Changes in branchial and intestinal osmoregulatory mechanisms and growth hormone levels during smolting in hatchery‐reared and wild brown trout
Authors: Nielsen C. , Madsen S. S. , Björnsson B. Th.
Published: April 2005

Evidence of smolting was studied in Danish hatchery‐reared brown trout Salmo trutta L. Twenty‐four hour seawater (SW) challenge tests (28‰, 10°C) at regular intervals showed that maximal hypo‐osmoregulatory ability developed within a 3–4‐week period in March and April. The improved ability to regulate plasma osmolality, muscle water content and plasma total [Mg] developed asynchronously, indicating that developmental changes in the gill, the gastrointestinal system and the kidney may not necessarily concur during smolting. Gill Na+, K+‐ATPase activity peaked in April at the time of optimal hypo‐osmoregulatory ability. Na+, K+‐ATPase a ‐subunit mRNA level in gills was unchanged from January until April, but decreased in May in parallel with a decrease in the activity of the enzyme. In the middle region of the intestine, Na+, K+‐ATPase activity increased in February and remained high until April. In the posterior region of the intestine, the activity was stable from January until April after which it decreased. In vitro fluid transport capacitity, Jv, in the middle intestine fluctuated throughout the spring. In the posterior intestine, Jv was low until late March, when it increased fivefold until early May. Drinking rate in fish transferred to SW for 24 h surged during spring. Na+, K+‐ATPase activity in the pyloric caeca was elevated from March until May, and increased in response to SW transfer in June, suggesting a hypo‐osmoregulatory function of the pyloric caeca. Plasma GH levels surged in FW trout during spring, concurring with the increase in gill Na+, K+‐ATPase activity and SW tolerance, but peaked in May when gill Na+, K+‐ATPase activity and SW tolerance were regressing. GH levels were generally low in SW‐challenged fish, and there was no consistent effect of 24‐h SW exposure on GH levels. In wild anadromous trout, gill Na+, K+‐ATPase activity varied seasonally as in hatchery‐reared fish, but peaked at higher levels suggesting a more intense smolting in fish living in their natural environment.
Early development and allometric growth patterns in Siberian sturgeon and their ecological significance
Authors: Gisbert E.
Published: April 2005

Early development of Siberian sturgeon Acipenser baeri was divided into two different phases, the prelarval stage between hatching (10·4–11·1 mm LT) and first feeding (19·6–21·0 mm LT), and the larval stage between the initiation of external feeding and metamorphosis (28·6–32·4 mm LT). Morphogenesis and differentiation were more intense during the prelarval than larval and early juvenile stages; the prelarval period was characterized by the replacement of embryonic adaptations and functions by definitive ones, such as branchial respiration, exogenous feeding, and active swimming. The positive allometry of the head for feeding, sensorial and respiratory functions (inflexion point at 20·0 mm LT), and the tail for reducing costs of transport, routine swimming and escape reactions from predators (inflexion point at 20·2 mm LT) confirmed the hypothesis that growth patterns of early life stages closely match specific needs.
Effects of aluminium and cortisol on in vitro calcium deposition on otoliths in rainbow trout
Authors: Mugiya Y. , Tohse H. , Katoh S.
Published: April 2005

Aluminium (1–100 μM) reduced in vitro calcium deposition on otoliths concentration‐dependently in rainbow trout, but cortisol (1 and 10 μg ml−1) had no effect.
The influence of a power station on the survival of juvenile sea bass in an estuarine nursery area
Authors: Pawson M. G. , Eaton D. R.
Published: April 2005

Trawl surveys in the estuary of the River Medway in the autumns of 1987–1991 have shown that the distribution of juvenile sea bass Dicentrarchus labrax is strongly associated with the warm‐water outflow from Kingsnorth power station. In years of low abundance of first‐year bass, very few were caught outside the warm‐water discharge channel, whereas proportionately more fish of abundant year classes occupied the main river. About 15% of the available juvenile bass population died on the cooling‐water intake screens at Kingsworth in the autumn and winter of 1987 and 1988. However, growth and survival of first‐year bass in the Medway Estuary may be enhanced by the power station's warm‐water effluent, such that overwinter mortality due to inadequate nutritional reserves and low temperatures may be considerably reduced.
Population stability of the sea snail at the southern edge of its range
Authors: Henderson P. A. , Seaby R. M.
Published: April 2005

The sea snail Liparis liparis population in the Bristol Channel on the Atlantic coast of Britain is close to the south‐western extremity of its range and yet it is one of the more abundant species present. Using a 17‐year time series of monthly samples collected at Hinkley Point power station in Bridgwater Bay, Somerset, U.K., the coefficient of variation of annual abundance of sea snail was estimated as 70·48%. Analysis of variance of the six replicate time series showed that 94% of the total variance was attributable to between‐year variation in local abundance and only 6% to sampling error. A comparison of the coefficients of variation in the annual number of captures of all the common fish found that the sea snail had one of the more stable populations in the estuary and bottom‐living fish tended to show the lowest variability in population number. Arguments based on either the assumed maladaptation of populations at the periphery of their geographical range or the rapid response of short‐lived animals to change would have predicted sea snail to have one of the more variable populations. As might be expected for a fish adapted to cooler, more northern and eastern waters, sea snail winter abundance was negatively correlated with seawater temperature. Using the unusual oscillation in water temperature observed during the winter of 1996/1997, it is argued that the correlation of sea snail abundance with temperature reflects changes in distribution rather than mortality, with the fish avoiding inshore waters in warm winters. It is hypothesized that demographic plasticity and biotic interactions such as parasite and pathogen attack can result in fish populations showing neither latitudinal nor longitudinal trends of increasing population variability from the centre towards the periphery of the range.
Mitochondrial genealogy of Western Australian barramundi: applications of inbreeding coefficients and coalescent analysis for separating temporal population processes
Authors: Doup R. G. , Horwitz P. , Lymbery A. J.
Published: April 2005

In Australian populations of barramundi Lates calcarifer, phylogenetic reconstruction of mtDNA sequences provided evidence of significant historical levels of gene flow, despite the substantial structuring of contemporary populations. The geographical pattern of mtDNA sequences among the populations was not congruent with previous evidence of a major disjunction between western and eastern populations of barramundi in Australia.
Genetic differentiation among Atlantic cod in south and south‐east Icelandic waters: synaptophysin (Syp I) and haemoglobin (HbI) variation
Authors: Jónsdóttir Ó. D. B. , Imsland A. K. , Daníelsdóttir A. K. , Thorsteinsson V. , Nævdal G.
Published: April 2005

Significant differences were found at the synaptophysin (Syp I) locus between two groups of Icelandic cod Gadus morhua; Loftstaõahraun (spawning ground), Reykjanesgrunn and Eyrabakkabugur (feeding grounds) on the one hand and Kantur (spawning ground) and Austfjarõadjúp (feeding ground) on the other. There was also a considerable genetic heterogeneity within the former group. The results indicate that the cod in south and south‐east Icelandic waters do not belong to one panmictic population.
Morphological correlates of diet in an assemblage of West African freshwater fishes
Authors: Hugueny B. , Pouilly M.
Published: April 2005

Morphological correlates of diet were sought among 18 species of distantly related freshwater fishes from Guinea (West Africa). With regard to the percentage occurrence of six food items, the studied species could be classified into four broad trophic categories reflecting what was eaten and where: detritivores, piscivores, surface feeders and benthic invertivores. Detrivory was associated with a high relative gut length and eyes in a dorsal position; piscivory with large body and mouth size; surface feeding with a dorsally orientated mouth; and benthic invertivory with eyes in a lateral position and small relative gut length. Similarity in diet and in morphology were both significantly correlated with taxonomic relatedness. Nevertheless, when taxonomic relatedness was accounted for, the relationship between observed similarity in diet and similarity in diet predicted from morphology was still significant. This result leads to the conclusion that species having similar diet tend to converge for some morphological attributes.
First inland records of the euryhaline goby Knipowitschia caucasica from lakes in Anatolia, Turkey
Authors: Neer W. Van , Wildekamp R. H. , Küccedel;ük F. , Unlüsayin M.
Published: April 2005

Knipowitschia caucasica, a euryhaline Ponto‐Caspian‐Aegean gobiid fish, is recorded for the first time from Lakes Eǧirdir, Eber and Demirköprü (Anatolia). Its presence in these lakes is probably due to involuntary introduction with common carp from hatcheries in the Edirne‐Ipsala region, Thrace, the European part of Turkey.
Feeding ecology of juvenile flatfishes of the surf zone of a sandy beach
Authors: Besyst B. , Cattrijsse A. , Mees J.
Published: April 2005

Prey items of 0‐ and 1‐group plaice Pleuronectes platessa, sole Solea solea, brill Scophthalmus rhombus, turbot S. maximus and dab Limanda limanda of the surf zone of a Belgian sandy beach, included hyperbenthic (e.g. mysids), endobenthic (e.g. polychaetes) and epibenthic (e.g. shrimps) species. Little dietary overlap was observed. If diet overlap did occur, it mainly involved prey species that are dominant in the surf zone of Belgian beaches, such as shrimps and mysids. These results suggest an opportunistic utilization by flatfish of the available food resources in surf zone ecosystems. Also, two strategically different feeding habits could be distinguished between the five flatfish species. Turbot and brill mainly fed on large, highly mobile prey (e.g. fish, mysids) and had a rather narrow prey spectrum, whereas plaice, dab and sole ate more benthic prey (e.g. polychaetes) and had a broader prey spectrum.
Egg cannibalism in river blennies: the role of natural prey availability
Authors: Vinyoles D. , Côté† I. M. , De Sostoa A.
Published: April 2005

The abundance of benthic macro‐invertebrates, the main prey of river blenniesSalaria fluviatilis, decreased drastically through the blenny reproductive season in the River Matarraña, south‐east Spain. Despite this, females maintained their body condition, while the body condition of males increased. The latter coincided with the onset of egg guarding, which is carried out by males and which provided them with an opportunity to cannibalize eggs. Indeed, significantly more males than females were egg cannibals. The proportion of cannibalistic males increased as the season progressed, but the overall frequency remained low (7·4%). The number of eggs eaten was not related to the weight of macro‐invertebrates ingested by males. In addition, the body condition of cannibalistic and non‐cannibalistic males was similar and was not correlated with the number of eggs ingested. It is possible that non‐cannibalistic males may have eaten and digested eggs prior to capture. It is concluded that even in productive rivers such as the Matarraña, males may still rely on filial cannibalism to survive until the end of the parental care period.
Alarm pheromones of rainbow darters: responses to skin extracts of conspecifics and congeners
Authors: Commens A. M. , Mathis A.
Published: April 2005

Rainbow darters Etheostoma caeruleum exposed to extracts from macerated skin of both conspecifics and of yoke darkers E. juliae responded with decreased activity. Both species have epidermal sacciform cells that are candidates as the source of the pheromone.