The angle of attack of the body of common bream while swimming at different speeds in a flume tank

The body attack angle of common bream Abramis brama varied with swimming speed and was best described by θ = −3·32 (±0·24) − 9·23 (±0·54)e^{− u} ( r ² = 0·56, P  < 0·0001; ±1 s . e . given in parentheses), where θ is the body attack angle and u is swimming speed. The hypothesis that neutrally buoyant fishes may swim with body attack angles deviating increasingly from 0° as the swimming speed decreases is supported.     

Early growth and juvenile population structure of lemon sharks Negaprion brevirostris in the Atol das Rocas Biological Reserve, off north‐east Brazil

Lemon sharks Negaprion brevirostris were sampled in the Atol das Rocas, a nursery area, on nine occasions from March 1999 to October 2003, during which 157 individuals were tagged and 35 were recaptured. The male : female sex ratio of captured individuals was 1 : 1·12. Mean ±  s . d . growth rates were 24·7 ± 3·4 cm year⁻¹ in total length ( L _T), 20·7 ± 3·2 cm year⁻¹ in fork length, and 19·5 ± 2·7 cm year⁻¹ in precaudal length. There was no significant difference in growth rates between males and females. Mean ±  s . d . increase in mass was 2565 ± 762 g year⁻¹. The von Bertalanffy growth parameters estimated by the Fabens method based on L _T were: k  = 0·077, L _∞ = 399·9 cm and t ₀ = −2·16. Despite the large variation of environmental conditions, particularly of tidal range and currents, and the lack of protective mangrove cover in the nursery area at Atol das Rocas, juvenile lemon sharks grew relatively faster than at other nurseries. Such rapid growth could be a response to abundant food availability or high risk of predation by adults that enter the nursery area.     

A field and experimental evaluation of the effect of data storage tags on the growth of cod

The effect of electronic data storage tags (DSTs) on the growth of cod Gadus morhua was evaluated in laboratory and field experiments. In the first laboratory experiment, large DSTs (60 × 18 mm, 3 g in water ) attached externally for 3 months did not have any effect ( anova , P  > 0·05) on the growth of adult cod (mean ±  s . d . 65 ± 4·5 cm total length) relative to untagged adult cod. In a second experiment, small DSTs (34 × 11 mm, 1·5 g in water) implanted into young cod (48·1 ± 4·4 cm) for an 8 month period did not have any effect upon the growth relative to untagged controls ( anova , P  > 0·05). Length data returned from tagging experiments conducted on adult cod (57·3 ± 7·5 cm) in the North Sea showed that the growth of fish tagged either externally or internally with large DSTs was not different ( t ‐test, P  > 0·05). Attachment wounds, however, provided evidence that external attachment of DSTs should be avoided unless sensor configuration requires access to the external environment, and that internal implantation should be preferred whenever possible.     

Haematology and leucocyte morphology of wild caught Thunnus maccoyii

The haematology of wild southern bluefin tuna Thunnus maccoyii was described using blood samples collected from fish immediately after they were caught. Cytology and cytochemistry revealed that the blood in peripheral circulation is comprised of erythrocytes, reticulocytes, ghost cells, lymphocytes, thrombocytes, eosinophilic granulocytes, neutrophilic granulocytes and monocytes. Reference ranges established were 41·09–55·50% for haematocrit, 0·62–3·00% for leucocrit, 13·25–17·92 g dl⁻¹ for haemoglobin and 2·1–2·9 million erythrocytes μl⁻¹ for erythrocyte count. Differential cell counts showed 94·58 ± 2·15% erythrocytes, 3·99 ± 1·44% leucocytes and 1·43 ± 1·03% thrombocytes (mean ±  s . d .). Normal ranges for differential leucocyte counts were 0·00–5·45% for neutrophils, 0·69–12·06% for eosinophils, 0·00–5·03% for monocytes, 46·97–74·32% for lymphocytes and 14·47–43·92% for thrombocytes. Erythrocyte indices, leucocyte types and cytochemistry were comparable to other species of scombrids. Packed cell volume was sensitive to the physiological state of the fish and to sample handling technique.     

The genetic architecture of correlations among growth‐related traits and male age at maturation in rainbow trout

Heritabilities and genetic correlations among growth‐related traits of two cultured strains (Rainbow Springs and Spring Valley) of rainbow trout Oncorhynchus mykiss were estimated using restricted maximum likelihood methods with a three‐generation pedigree. Heritability was high (>0·50 ± 0·03) for body mass and condition factor but moderate (0·35 ± 0·04) for age at sexual maturity in males. Body mass and age at sexual maturation were phenotypically correlated in the families of one experimental strain, Rainbow Springs, and had a positive genetic correlation (0·26 ± 0·03) across families from both test strains (Rainbow Springs and Spring Valley). This indicates that faster growing individuals were more likely to mature at 2 years of age than slower growing individuals in the two hatchery strains investigated. Microsatellite markers of body mass quantitative tract loci (QTL) were reconfirmed as being located on linkage groups B, G, N, 5 and new markers on Oi were detected. Some QTL effects were restricted to specific sampling dates suggesting temporal expression of QTL. QTL for condition factor were limited to linkage group G in both strains. Three suggestive QTL for precocious maturation mapped to similar regions as those for body mass in the Rainbow Springs families while no associations were evident in the Spring Valley families. The results suggest that these regions may play a role in the basis for genetic and phenotypic correlations between body mass and precocious maturation in this species.     

Spawning characteristics of the anadromous brown trout in a small Swedish stream

The spawning pattern of the anadromous brown trout Salmo trutta was studied in Själsöån, a small stream in Gotland, Sweden, during eight winters between 1992–1993 and 1999–2000. The total length ( L _T) at spawning was normally distributed (185–890 mm) for females and multimodal for males (300, 400 and 550 mm most frequent length classes). Spawning males were significantly younger (2+ to 4+ years) than females (3+ to 5+ years). The sex‐ratio at the beginning and at the end of the spawning season favoured males. The mean ±  s . d . number of spawners was 70 ± 16 individuals per year. Migration into and out of the stream occurred between November and June. The highest number of spawning fish was found in the stream at the end of November or at the beginning of December. Migration mainly occurred during high water flow and at night. The majority of the females entered the stream and spawned the same (29·3% of all the females) or the next night (32·8% of all the females) while males may have stayed for 2 to 3 weeks (21·3% of all the males) in the stream before spawning. Males usually remained much longer in the stream (mean ±  s . d . 45 ± 56 days) than females (16 ± 30 days). Females lost more mass in the stream (mean ±  s . d . 17·3 ± 8·6%) than males (7·7 ± 9·6%). For both sexes, mass loss was positively correlated with the time spent in the stream. Only 7·3% of the males and 5·7% of the females occurred in the stream for >1 year. Spawning took place only during the night.     

Mitochondrial DNA sequence divergence between two cryptic species of Lethenteron, with reference to an improved identification technique

Genetic divergences and population structures were examined in the cryptic Lethenteron sp. N and sp. S, based on mitochondrial DNA (mtDNA) cytochrome oxidase subunit I (CO I) region sequences. An improved method of discrimination between L . sp. N and sp. S was found using PCR, with diagnostic primers for each species-specific sequence in the mtDNA CO I region. Identification of 50 individuals of each species by this analysis was consistent with that by allozyme analysis of nuclear DNA. L . sp. N and sp. S, identified on the basis of diagnostic alleles at five allozymic loci, were independently grouped in a neighbour-joining (NJ) tree, with a large sequence difference (mean ±  s . d . = 9·10 ± 0·36%) between them. Within each species, the values of sequence divergence among localities were significantly higher in L . sp. S (1·61 ± 0·44%) than in L . sp. N (1·10 ± 0·48%). On the tree and nested clade analyses, several phylogenetic groups comprising geographically close localities were detected in the former, although scarcely detected in the latter, probably resulting from dispersal pattern differences between them.     

Variation in the sex ratio, size and age of longfinned eels within and among coastal catchments of south‐eastern Australia

Longfinned eels Anguilla reinhardtii were captured by both fishery‐dependent and independent sampling methods from three rivers in New South Wales, south‐eastern Australia. Sex ratios, catch per unit effort and population age and total length structure were examined in three zones (fresh water and upper and lower tidal) in the Hacking, Hawkesbury and Clarence Rivers. Females were found in relatively high proportions in all zones, ranging from 97% in a freshwater (non‐tidal) site down to 59% in a tidal site. Males were found primarily in tidal zones (only two of the 677 longfinned eels caught in non‐tidal fresh water were males), with the greatest proportions being found in the brackish upper tidal areas. The mean number of fish captured per trap was higher in the fresh water and upper tidal zones than in the lower tidal zones. The mean ±  s . e . age, 17·9 ± 0·3 years, and age range, 5–52 years for females were significantly higher than those of males 12·2 ± 0·4 years; range 5–22 years, which is typical of other anguillid species. Longfinned eels captured in fresh water were found be significantly larger and older than those in tidal zones due to the almost exclusive predominance of females.     

Endurance swimming of diploid and triploid Atlantic salmon

When groups of diploid (mean ±  s . e . fork length, L _F) 33·0 ± 1·4 cm and triploid (35·3 ± 0·5 cm) Atlantic salmon Salmo salar were forced to swim at controlled speeds in a carefully monitored 10 m diameter 'annular' tank no significant difference was found between the maximum sustained swimming speeds ( U _ms, maintainable for 200 min) where the fish swam at the limit of their aerobic capability. Diploids achieved 2·99 body lengths per second (bl s⁻¹)(0·96 m s⁻¹) and triploids sustained 2·91 bl s⁻¹(1·02 m s⁻¹). The selection of fish for the trials was based on their ability to swim with a moving pattern projected from a gantry rotating at the radius of the tank and the selection procedure did not prove to be significant by ploidy. A significant difference was found between the anaerobic capabilities of the fish measured as endurance times at their prolonged swimming speeds. During the course of the experimentation the voluntary swimming speed selected by the fish increased and the schooling behaviour improved. The effect of the curvature of the tank on the fish speeds was calculated (removing the curved effect of the tank increased the speed in either ploidy by 5·5%). Implications of the endurance times and speeds are discussed with reference to the aquaculture of triploid Atlantic salmon.     

Description of a new Lake Tanganyikan cichlid fish of the genus Cyprichromis(Perciformes: Cichlidae) with a note on sexual dimorphism

Cyprichromis coloratus , a new cichlid species, is described based on 41 type specimens from the Zambian coast of Lake Tanganyika. It differs from Cyprichromis microlepidotus by having fewer scales in the longitudinal line (41–44 v . 59–70 in C. microlepidotus ) and upper lateral line (31–36 v . 47–59), from Cyprichromis leptosoma by more dorsal‐fin spines (14–15 v . 11–13 in C. leptosoma ) and longitudinal line scales (41–44 v . 38–40), from Cyprichromis pavo by fewer dorsal‐fin spines and soft rays (29–31, usually 30, in total v . 30–32, usually 31, in C. pavo ), and from Cyprichromis zonatus by shallower body depth [24·0–28·5 (26·4 ± 1·1)% of standard length v . 24·5–30·5 (28·4 ± 1·3)% in C. zonatus ] and smaller eye [eye length 25·2–30·9 (27·2 ± 1·1)% of head length v . 27·9–33·3 (30·2 ± 1·2)%]. The new species is also separable from C. microlepidotus , C. pavo and C. zonatus by absence of distinct small spots on the body ( v . pearl grey and yellowish small spots along scale rows on body at least in males of C. microlepidotus and C. pavo ), its distinct dichromatism (particularly on the caudal fin) between males of the same population ( v . dichromatism absent in C. zonatus ) and absence of vertical bands ( v . three or four distinct vertical bands beneath dorsal fin base in live males of C. zonatus ). Cyprichromis coloratus n. sp. also exhibits sexual dimorphism, females having a larger head and males having longer pelvic fin, differences which are discussed in relation to reproductive behaviour. A key to the five species of Cyprichromis is included. A lectotype is designated for Cyprichromis leptosoma .     

Interannual and regional variations in body length, weight and energy content of age-0 Pacific herring from Prince William Sound, Alaska

Age-0 Pacific herring were surveyed in October of 4 years in a large northern Gulf of Alaska estuary, to determine the range of variations in length, weight and whole body energy content (WBEC). These parameters reflect their preparedness for surviving their first winter's fast. During the surveys there were distinct regional and interannual variations in all three parameters for individual groups of herring in Prince William Sound. Likewise, with each collection there was typically a large range of size and WBEC values. The average standard length was (±S.D.) 80±13 mm (range=40–118), the mean whole body wet weight was 5·7±3·0 g (range=0·7–29·2) and the average WBEC of all age-0 herring captured, regardless of year or site (n=1471), was 5·4± 1·0 kJ g⁻¹ wet weight (range=2·4–9·4). The large range of WBEC and size indicates that age-0 herring at different capture sites were not all equally prepared for surviving their first winter.     

Effect of delayed first feeding on development and feeding ability of Paralabrax maculatofasciatus larvae

The impact of delayed feeding early in development on late feeding ability and development of spotted sand bass Paralabrax maculatofasciatus larvae was examined. Larvae were sampled from hatching until day 19 after delayed feeding for zero (control), 1, 2, or 3 days. Feeding incidence was evaluated as the percentage of larvae with food in the gut and feeding intensity was measured by direct counting of prey after dissection of the gut. Delayed feeding effects due to starvation were observed early in development. By day 5, significant differences ( P  < 0·05) were observed between controls and larvae submitted to degrees of delayed feeding, including total length ( L _T), eye diameter, and the size of the head, liver, gut, muscles and body. Differences were still apparent in L _T, and body, liver and muscle heights at the end of the studied period. Larvae under total starvation did not survive beyond day 5. Initial feeding incidence was 35, 60, 90 and 10% for larvae first fed on day 2, 3, 4 or 5, respectively. Mean ±  s . d . feeding intensity was 3·6 ± 0·8, 2·8 ± 1·3, 5·2 ± 0·3, and 10·2 ± 1·5 rotifers per larva depending on whether larvae were initially fed on day 2, 3, 4 or 5, respectively. The point of no return occurred between 4 and 5 days after hatching.     

Morphometric recognition of two morphs in sterlet (Acipenser ruthenus) population induced by different reproductive behaviour

Four species of sturgeons appear in the Yugoslav part of the Danube River. Among them three are anadromous, beluga ( Huso huso ), Russian sturgeon ( Acipenser gueldenstaedtii ) and stellate sturgeon ( Acipenser stellatus ) and migrate to Danube from the Black Sea to spawn. Only sterlet ( Acipenser ruthenus ) is exclusively freshwater. There are obvious differences between vernal and winter races of anadromous sturgeons, due to their different migratory patterns. Russian ichthyologist Berg (1934) claimed that there are two races (morphs) in the starlet population as well. This stimulated long discussion in Russian and Yugoslav literature, and it was the starting point for our research on sterlet in the Yugoslav part of the Danube River.
Morphometric analysis was preformed on 159 individuals caught in Danube River among 1123 and 1173 km, on four localities during September and October 2002. Analysis included 24 morphological and 3 meristic characters. K‐means cluster analysis indicated existence of two different clusters (groups), one with 95 (59·75%) and other with 64 (40·25%) samples. Significant differences were found for preorbital, preoral and prebarbel length. Mean values (in % of head length) for first group were 50·13 ± 1·71, 57·61 ± 1·87, 39·74 ± 2·20 and for second group 53·50 ± 2·46, 62·07 ± 2·20 and 43·30 ± 2·08 respectively. Findings were confirmed by Principal Components & Classification Analysis. These results speak in favour of existence of two morphs in sterlet population, one with long and pointed rostrum (vernal) and other with short rostrum (winter). According to the literature that is probably influenced by different reproductive behaviour (time separation in spawning).     

Lack of gas bladder inflation by the larvae of zebrafish in the absence of an air-water interface

Compared to a control gas bladder inflation rate of 95·1±1·9%, zebrafish Danio rerio larvae 72 h post-fertilization maintained in closed chambers had an inflation rate of just 19·1±7·7%. Larval survivorship through 10 days in closed chambers (32%) was significantly less than that in open chambers (76%), and the extent of spinal curvature was significantly higher among larvae maintained in closed chambers. Larvae which failed to inflate their gas bladder showed very little change in body length, and had a final dry weight c. 14% of that for control larvae. The small number of larvae with inflated gas bladders found in closed chambers might be attributed to the inadvertent introduction of small bubbles into two replicates. These results indicate that access to an air-water interface is critical for the normal development of zebrafish larvae, but also that a small, submerged, spherical gas volume may to a limited extent be used for initial gas bladder inflation.     

Physiological impact of sea lice on swimming performance of Atlantic salmon

Atlantic salmon Salmo salar were infected with two levels of sea lice Lepeophtheirus salmonis (0·13 ± 0·02 and 0·02 ± 0·00 sea lice g⁻¹). Once sea lice became adults, the ventral aorta of each fish was fitted with a Doppler cuff to measure cardiac output ( ̇ ), heart rate ( f _H) and stroke volume ( V _S) during swimming. Critical swimming speeds ( U _crit) of fish with higher sea lice numbers [2·1 ± 0·1 BL (body lengths) s⁻¹] were significantly lower ( P  < 0·05) than fish with lower numbers (2·4 ± 0·1 BL s⁻¹) and controls (sham infected, 2·6 ± 0·1 BL s⁻¹). After swimming, chloride levels in fish with higher sea lice numbers (184·4 ± 11·3 mmol l⁻¹) increased significantly (54%) from levels at rest and were significantly higher than fish with fewer lice (142·0 ± 3·7 mmol l⁻¹) or control fish (159·5 ± 3·5 mmol l⁻¹). The f _H of fish with more lice was 9% slower than the other two groups at U _crit. This decrease resulted in ̇ not increasing from resting levels. Sublethal infection by sea lice compromised the overall fitness of Atlantic salmon. The level of sea lice infection used in the present study was lower than has previously been reported to be detrimental to wild Atlantic salmon.     

Predator‐induced hyperventilation in wild and hatchery Atlantic salmon fry

Following exposure to a predator stimulus (a brown trout Salmo trutta ), the opercular rate of Atlantic salmon Salmo salar fry increased by 35·3 ± 11·0%(mean ± 95% CI). The time taken for opercular rate to decline to baseline levels depended upon the occurrence of any associated locomotory activity. Opercular rates of fish that dashed when exposed remained elevated for 38·2 ± 20·6 min, whereas those of individuals that did not move ('freezers') recovered within 7·2 ± 2·9 min. The duration that opercular rate remained elevated was positively correlated with the magnitude of the elevation, which was higher in 'dashers' than freezers. The maximum opercular rate in 'freezers' was similar between wild fry and hatchery‐reared fry (from wild parents). There was a significant delay, however, in hatchery compared with wild fry in the time until peak ventilatory response and onset in the decline phase. This difference in opercular response suggests that hatchery fish were slower to realize fully the potential danger from the predator. Any delay in response could be directly attributed to the effect of hatchery‐rearing environment, rather than domestication or hatchery selection effects.     

Morphological and mitochondrial DNA divergence validates blackmouth, Galeus melastomus, and Atlantic sawtail catsharks, Galeus atlanticus, as separate species

A total of 60 morphometric traits and nucleotide sequences of the entire mtDNA NADH dehydrogenase subunit 2 (ND2) gene [1047 base pair (bp)] in 23 individuals of blackmouth, Galeus melastomus , and 13 individuals of sawtail catsharks, Galeus atlanticus , caught in Southern Portugal, were examined to test the validity of these two taxa. These sharks closely resemble each other, have overlapping geographical ranges and are difficult to identify by morphological characters. Non-metric multidimensional scaling of morphometric variables indicates a clear separation between the two species, with 10 characters each contributing 2·12–2·45% of the total variability between species. Maximum likelihood, parsimony and neighbour-joining trees revealed two major mtDNA haplotype clades, corresponding to the two species, with an average corrected sequence divergence between them of 3·39 ± 0·56%. Within species divergences between haplotypes averaged 0·27 ± 0·18% in G. melastomus and 0·12 ± 0·08% in G. atlanticus . A total of 35 diagnostic nucleotide site differences and four restriction fragment length polymorphism recognition sites in the ND2 gene can be used to distinguish the two species.     

Migration of hatchery‐reared Atlantic salmon and wild anadromous brown trout post‐smolts in a Norwegian fjord system

Hatchery‐reared Atlantic salmon Salmo salar ( n  = 25) and wild anadromous brown trout (sea trout) Salmo trutta ( n  = 15) smolts were tagged with coded acoustic transmitters and released at the mouth of the River Eira on the west coast of Norway. Data logging receivers recorded the fish during their outward migration at 9, 32, 48 and 77 km from the release site. Seventeen Atlantic salmon (68%) and eight sea trout (53%) were recorded after release. Mean migratory speeds between different receiver sites ranged from 0·49 to 1·82 body lengths (total length) per second (bl s⁻¹) for Atlantic salmon and 0·11–2·60 bl s⁻¹ for sea trout. Atlantic salmon were recorded 9, 48 and 77 km from the river mouth on average 28, 65 and 83 h after release, respectively. Sea trout were recorded 9 km from the release site 438 h after release. Only four (23%) sea trout were detected in the outer part of the fjord system, while the rest of the fish seemed to stay in the inner fjord system. The Atlantic salmon stayed for a longer time in the inner part than in the outer parts of the fjord system, but distinct from sea trout, migrated through the whole fjord system into the ocean.     

The role of the pectoral fins in body trim of sharks

In a large aquarium the leopard shark Triakis semifasciata , sand tiger shark Odontaspis taurus , sandbar shark Carcharhinus plumbeus , and spiny dogfish Squalus acanthias cruised steadily at 0·1-0·7 body lengths s^-1. Relative to the trajectory of the shark, the pectoral fins were maintained at a positive angle of ttack regardless of vertical direction. For level swimming the mean angle of attack for the pectoral fin was 11±1·7, 10·1±1·3°, 9·3±1·3°, and 15·0±0·0 for T. semifasciata , C. plumbeus , O. taurus , and S. acanthias , respectively. The long axis of the body was canted at an angle of attack for T. semifasciata and S. acanthias , but trim was maintained during level swimming for C. plumbeus and O. taurus . Hydrodynamic analysis of the body and fin design of T. semifasciata indicated that the pectoral fins could develop suffcient pitching moment to maintain depth and keep the body in trim. Demonstration of positive angles of attack support the hypothesis that lift is generated in the anterior body to counterbalance the lift produced by the heterocercal tail.     

Parasitic isopods (Gnathia sp.) reduce haematocrit in captive blackeye thicklip (Labridae) on the Great Barrier Reef

Captive Hemigymnus melapterus exposed to large numbers of cultured juvenile parasitic isopods ( Gnathia sp.) had significantly lower haematocrit (median 27·62% ± 5·83% inter‐quartile range) than uninfected, control fish (median 32·73% ± 4·90%). This study is the first to show that juvenile Gnathia sp. reduce total blood volume in H. melapterus . The low haematocrit in infected fish was most likely due to plasma replacing erythrocytes lost as a result of isopods feeding on fish blood.