Age and growth of Anguilla anguilla in the Camargue lagoons

Age and total length ( L _T) data from a 11 year monitoring of the Anguilla anguilla eel population of the Camargue lagoons (Rhône delta, southern France) were collected for glass, yellow and silver eels. Three distinct models were calibrated to describe the growth process of undifferentiated eels, females and males, respectively. Uncertainty of parameter estimates was evaluated by bootstrapping. Females were characterized by larger asymptotic body size ( L _T) than males (580 ± 50 v . 388 ± 13 mm) and faster growth, whilst the Brody growth coefficient was larger for males than for females (means ±  s . d . 3·00 10⁻³ ± 1·68 10⁻³ v . 1·73 10⁻³ ± 0·50 10⁻³). Sexual differentiation was estimated to begin at 204 ± 38 mm mean ±  s . d ., i.e . at the end of the second year in the lagoons, well before the L _T at which macroscopic differentiation became possible ( c . 300 mm). Males probably leave the lagoon or die (due to either natural or fishing mortality) within the first 3 years, whilst females can remain up to 5 years. Sexual differentiation and maturation have a major role in shaping the L _T structure of the population. The L _T and mass ( M ) data were fitted by allometric curves     . The calibration of distinct curves for data from different years indicated that the allometric coefficient a was subject to wider interannual fluctuations than the allometric exponent b . A negative correlation linked the average L _T and the allometric exponent ( r  = −0·58, P  < 0·01).     

Low activity and seasonal change in population size structure of grenadiers in the oligotrophic abyssal central North Pacific Ocean

Analysis of video recordings of swimming in abyssal grenadiers Coryphaenoides spp. revealed site differences in tail-beat frequencies. At the highly oligotrophic deep central North Pacific (CNP; 5800 m depth) station fishes had significantly lower tail-beat frequencies (0·73 ± 0·02 Hz, mean ±  s . e .) than fishes of similar size at the shallower 'Station F' (Sta. F; 4400 m depth) beneath the more productive waters of the California Current Upwelling (1·06 ± 0·04 Hz). These behavioural differences may be evidence for the proposed physiological adaptations of Coryphaenoides armatus and Coryphaenoides yaquinae , to different depths and food supply levels. At CNP, smaller fishes (38·9 cm mean L _T) were present in autumn than in summer (59·4 cm L _T) suggesting large-scale migrations across the abyssal ocean floor despite the observed slow swimming speeds.     

A histological study on the development of the digestive system of Pseudosciaena crocea larvae and juveniles

The ontogenetic development of the gut and accessory organs in large yellow croaker Pseudosciaena crocea was investigated using light microscopy from hatching up to the juvenile stage (40 days post hatch, dph). At 3 dph (mean ±  s . d ., 4·1 ± 0·1 mm total length, L _T), coinciding with the buccopharynx opening, larvae started to feed exogenously, and the gut consisted of a well‐developed buccopharynx, a partially‐differentiated oesophagus and an intestine divided in three regions (anterior intestine, intermediate intestine and rectum). Yolk reserves were not completely depleted at the onset of exogenous feeding, and a period of mixed nutrition was observed up to 6 dph (4·3 ± 0·1 mm L _T), when yolk was definitively exhausted. Important morphological changes occurred at the end of the larval period, coinciding with metamorphosis. At 17 dph (6·8 ± 0·6 mm L _T), pyloric caeca differentiated at the junction of the pyloric stomach and the anterior intestine. Gastric glands were first observed at 21 dph (9·2 ± 1·2 mm L _T), coinciding with the morphological development of the stomach in three different regions (cardiac, fundic and pyloric) according to the histological characteristics of their mucosa. At this age, large longitudinal folds appeared in the median and posterior oesophageal mucosa. These morphological and histological features suggested the achievement of a digestive system characteristic of large yellow croaker juveniles and adults.     

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.     

Some morphometric and biochemical features of ready-to-migrate silver and pre-migratory yellow stages of the shortfin eel of south-eastern Australian waters

The mean total length ( L _T), mass and age of ready to migrate female silver shortfin eels Anguilla australis from the Hopkins River estuary and the mouth of the Merri River in south-eastern Australia, were 83·2 ± 1·2 cm, 1051 ± 51 g, and 17·2 ± 1·79 years, respectively. The eye index ( I _E) of the silver shortfin eels was < 5·2 (mean 7·64 ± 0·29) and differed significantly from that of the yellow shortfin eels collected from two other sites. The I _E increased with L _T (mm) and was related by log I _E= 2·656 log L _T6·925. The per cent moisture, protein and ash content of the liver of silver shortfin eels was significantly lower than in yellow shortfin eels, but lipid content was significantly higher in the former (35·5 ± 2·0%). The mean mass μg mg lipid ⁻) of saturates (230·4 ± 2·6 v . 181·7 ±2·6), monoenes (367·4 ± 6·3 v . 290·8 ± 8·9) and PUFA (177·3 ± 5·3 v . 159·7 ± 4·6) in muscle was significantly higher, and the great majority of individual fatty acids was found also in higher quantities in silver shortfin eels. In the liver, the PUFA found in the highest quantity was 22:6n-3, except in shortfin eels from Hopkins River estuary, and the amount of 18:2n-6 in the liver of silver shortfin eels was significantly higher than that in yellow shortfin eels but the reverse was true of 20:4n-6. In both muscle and liver tissues the saturate 16:0 and the monoene 18:ln-9 collectively accounted for >50% of all the fatty acids in the lipid.     

Effects of river red gum, Eucalyptus camaldulensis, litter on golden perch, Macquaria ambigua

Aquaria with added river red gum, Eucalyptus camaldulensis , litter became hypoxic, with decreased pH and contained up to 30 mg 1⁻¹ tannin and lignin. Survival of golden perch, Macquaria ambigua , larvae in aquaria treated with a simulated annual litter density of 450 g m⁻² for 72 h was 14·9% for 15-day-old larvae and 0% for 8-day-old larvae. A litter density of 1223 g m⁻² resulted in total mortality for both age groups of larvae. Aeration increased survival of larvae to a minimum of 68·8% in 1223 g m⁻² litter treatments compared to 89·8% in aerated controls and 86·8% in non-aerated controls. A kinetic behavioural assay was used to detect alarm responses in golden perch larvae and juveniles exposed to leachates from river red gum bark, leaves and wood. Eight-day-old larvae exposed to bark and wood leachates (0·001–10 g 1⁻¹) exhibited an initial period of hyperactivity, followed by a concentration-dependent decrease in spontaneous activity. Larvae exposed to leaf leachates displayed only a decrease in spontaneous activity. Four-month-old juveniles exposed to wood leachates were also initially hyperactive, then progressively developed mild hypoactivity at increasing leachate concentrations. Juveniles exposed to wood leachates at 20g 1⁻¹ for 30min suffered 97·5% mortality in 96 h. Wood leachates induced dose-dependent lamellar fusion, epithelial dissociation and necrosis in the gills. The presence of toxic leachates and low oxygen availability in flooded river red gum forests may make these habitats unsuitable as nursery areas for native fish.     

Sublittoral abundance and food consumption of Baltic gobies

Two small demersal fishes, the sand goby Pomatoschistus minutus and the common goby Pomatoschistus microps , were quantified on soft bottoms at 20–40 m depth in the Baltic Sea, using a camera placed above the bottom. The largest numbers of gobies were seen following the settlement of young in late summer and autumn. Most recorded fishes were sand gobies. An annual average of 4·7 individuals m⁻²(0·24 g dry mass m⁻²) was recorded in 1983–1985 and 2·5 individuals m⁻²(0·13 g m⁻²) in 1997–1998. Using these densities, the annual goby food consumption was estimated to 100 kJ m⁻² in 1983–1985 and 50 kJ m⁻² in 1997–1998, corresponding to most of the annual macrobenthos production available to the gobies. The resulting goby production, assumed equal to 25% of the food consumed, must have been an important food source for the larger fishes occasionally recorded in the photographs.     

Stable isotope profiles of partially migratory salmonid populations in Atlantic rivers of Patagonia

In the present study, profiles of stable isotope composition were characterized for two species with partially migratory populations in rivers along the latitudinal gradient of Patagonia, brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss . The effects of factors ( e.g. ontogeny of fishes, location, species and fasting) that may influence the stable isotope analysis (SIA) were evaluated, as was SIA evaluated as a tool to assign individual fish to their corresponding ecotype. Anadromous fishes exhibited enriched δ¹⁵N (15·2 ± 1·0‰; mean ± s . d .) and δ¹³C (−19·2 ± 1·3‰) relative to resident fishes'δ¹⁵N (8·8 ± 1·1‰) and δ¹³C (−23·2 ± 2·5‰). For both species, the difference in δ¹⁵N was larger between resident (range 6·8–10·7‰) and anadromous (range 14·3–17·8‰) fishes than that in δ¹³C. Values of δ¹³C, while not as dramatically contrasting in rainbow trout, provided a powerful anadromy marker for brown trout in the region. Increases were found in both δ¹⁵N and δ¹³C during the spawning migration of anadromous rainbow trout, most likely due to fasting. Differences in stable isotopes between location, size and species were found, suggesting different stable isotopes base levels in freshwater environments and different trophic levels and feeding location of anadromous populations. The SIA was demonstrated as a powerful tool for ecotype discrimination in Patagonian Rivers, overriding any effect of sampling location, size or species.     

Habitat use and trophic position determine mercury concentration in the straight fin barb Barbus paludinosus, a small fish species in Lake Awassa, Ethiopia

The diet, habitat use and mercury concentration of the small fish species, the straight fin barb Barbus paludinosus , were studied in Lake Awassa, Ethiopia, for a period of 1 year from February 2003 to January 2004. Stable isotope signatures of nitrogen and carbon in different total length ( L _T) classes were used to determine trophic positions and organic carbon sources, respectively. Barbus paludinosus mainly occupied the protected benthic habitats (littoral and profundal) of the lake. The δ¹³C values were in the range from −24 to −19‰, indicating that the carbon source for B. paludinosus was benthic, as well. Small individuals (≤ 60 mm L _T) mainly preyed upon ostracods, intermediate sizes (60–100 mm) on aquatic insects and gastropods, while a tiny cyprinodont fish Aplocheilichthys antinorii dominated the diet of large individuals (100–160 mm). The progressively increase in δ¹⁵N with increasing L _T also indicated a diet shift towards piscivory in larger individuals. The mercury concentration ranging from 0·02 to 0·74 mg kg⁻¹ wet mass (wm), was unexpectedly high in this small species, and was significantly positively related to L _T, as well as to δ¹⁵N. Some large individuals had mercury concentrations < 0·1 mg kg⁻¹ wm, and low δ¹⁵N, indicating substantial variations in diet between individuals of same size. The study suggests that other piscivorous species which include B. paludinosus in their diet may have a high mercury intake risk.     

Depth distribution and biological characteristics of the European eel Anguilla anguilla in Lough Ennell, Ireland

Using a longline survey, a total of 196 European eels Anguilla anguilla were collected at different depths in Lough Ennell (maximum depth 30 m), central Ireland. The catch per unit of effort of A. anguilla that were caught from 1 to 25 m depths was lowest at 0·5–5·0 m and greatest at the deepest depth range (22·5–25·0 m). Sub-samples of A. anguilla from depths of <15 m showed little or no difference in size, sex ratio, age, growth rate, condition factor, length–mass relationship, gonado-somatic index, fin index or eye index with fish from depths of >15 m. All fish examined were female yellow-phase A. anguilla that had ages from 7 to 20 years (mean ± s . d . = 10·3 ± 2·9 years), with growth rates from 24·0–60·8 mm year⁻¹ (mean ± s . d . = 40·7 ± 8·5 mm year⁻¹). Variations in the growth rates were greater in the shallow group than that of the deep group. This study suggested that deeper regions are important feeding habitats for A. anguilla and that fish in this lake were growing moderately fast compared to similar habitats and areas in the species' range.     

Effects of cadmium chloride on the development of rainbow trout Oncorhynchus mykiss early life stages

The sub-chronic (28–56 days) effects of exposure to low concentrations of cadmium (Cd; 0·05, 0·25, 0·50 and 2·50 μg l⁻¹) shortly following fertilization on embryos, larvae and juvenile rainbow trout Oncorhynchus mykiss were examined. Premature hatching occurred at lower concentrations (0·05 and 0·25 μg l⁻¹ Cd), however, delayed hatching was seen in the 2·50 μg l⁻¹ Cd group, with >90% of hatching occurring on the last day of the hatching period. Larval growth was negatively affected by Cd exposure in a concentration-dependent manner. Larvae exposed to 2·50 μg l⁻¹ Cd were 13·9 ± 0·8% shorter in total length ( L _T) and weighed 22·4 ± 3·5% (mean ± s . e .) less than controls at the end of the exposure period. Plasma sex steroid concentrations (oestradiol in juvenile females and 11-ketotestosterone in juvenile males) were elevated (four- to 10-fold over controls) in exposed fish in both males and females, following 28 days of exposure to 0·05, 0·25 and 0·50 μg l⁻¹ Cd, respectively. These results suggest that environmentally realistic concentrations (in the μg l⁻¹ range) of Cd can affect the development of O. mykiss impacting embryos, larvae and juvenile fish.     

Surface free energies of oral streptococci

Abstract The surface free energies ( γ _b) of a variety of oral streptococci were determined from contact angle measurements on bacterial deposits, using the concept of dispersion and polar components. At least four strains of each species were tested. Strains of Streptococcus mutans, S. sanguis and S. salivarius possessed relatively high surface free energies (103 ± 12 mJ · m⁻²) and at the species level no significant difference was found. In contrast, the strains of S. mitis had remarkably low surface free energies (45 ± 14 mJ · m⁻²). S. milleri appeared to be a heterogeneous species, showing surface free energies over a range of 32–119 mJ · m⁻². No significant differences were observed between laboratory strains and strains freshly isolated from the oral cavity.     

The diet of ruffe Gymnocephalus cernuus (L.) in northern lakes: new insights from stable isotope analyses

The diet of ruffe Gymnocephalus cernuus was studied in two native populations in lakes of different productivity in south-west Finland using both traditional stomach content analyses and stable isotopes. According to stomach content analyses, chironomids were the most important prey type in both lakes and the diversity of the other prey reflected the zoobenthos community in the lake. Stable isotope analyses of carbon and nitrogen showed distinctive lake-specific and total length ( L _T)-related patterns in both δ¹³C and δ¹⁵N values, which could not be explained solely with diet changes. In the large mesotrophic Pyhäjärvi, both ¹³C and ¹⁵N isotopes became slightly enriched with increasing ruffe L _T, although stomach contents analyses did not suggest any diet change in larger ruffe. In the hypereutrophic Köyliönjärvi, the carbon isotope signatures of ruffe especially showed wide variation (−33·5 to −24·1‰), which was probably due to variable consumption of prey items with highly negative carbon isotope signatures. Overall, this study emphasizes that the interpretation of stable isotope results requires extensive background data of the system and that even then the diet composition of a consumer may be very difficult to define due to large variation in the signatures.     

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.     

Comparative effects of long-term hypoxia on growth, feeding and oxygen consumption in juvenile turbot and European sea bass

When juvenile turbot Scophthalmus maximus and sea bass Dicentrarchus labrax were fed to satiation, growth and food intake were depressed under hypoxia (3·2±0·3 and 4·5±0·2 mg O₂ l^-1). However, no significant difference in growth was observed between fishes maintained in hypoxia and fed to satiation and fishes reared in normoxia (7·4±0·3 mg O₂ l^-1) and fed restricted rations (same food intake of fishes at 3·2 mg O₂ l^-1). Routine oxygen consumption of fishes fed to satiation was higher in normoxia than in hypoxia due to the decrease in food intake in the latter. Of the physiological parameters measured, no significant changes were observed in the two species maintained in hypoxia. This study confirms the significant interaction between environmental oxygen concentrations, feeding and growth in fishes. Decrease in food intake could be an indirect mechanism by which prolonged hypoxia reduces growth in turbot and sea bass, and may be a way to reduce energy and thus oxygen demand.     

Biomass and production estimates of a fish community in a small South African estuary

The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m ⁻², was calculated at 55·89 g m⁻² year⁻¹. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m⁻² year⁻¹ accounted for <74% of the total fish production in this estuary.     

Growth response of pikeperch larvae in relation to body size and zooplankton abundance

The most critical period at onset of feeding in pikeperch Stizostedion lucioperca is short (<5 days at 20° C). The larvae are sensitive to prey density during the first week of exogenous feeding. First-feeding larvae of 6.5 mm total length ( L_T ) needed prey densities of >585 prey l⁻¹ to maintain mass (C_maint), whereas 5 days older larvae of 7 mm L _T C_maint= 55 prey l⁻¹ and for 11 mm L _T larvae C_maint<10 prey 1⁻¹. Changes in specific growth rates for larvae of 7 and 11 mm were similar to a type-II functional response curve reaching a specific growth rate of 26 and 30% day⁻¹, respectively, at 1000 prey l⁻¹, whereas the 6·5 mm larvae showed a linear growth response reaching a specific growth rate of only 9% day ⁻¹ at 1000 prey l⁻¹. The results suggest that prey density is a limiting factor, which might contribute to the high variation between year-class Strengths.     

The growth rate of eel in tributaries of the lower River Severn, England, and its relationship with stock size

The growth rate of 1980 eel Anguilla anguilla from 15 sites in the Severn system varied between 16·4 and 27·9 mm year^-1, density from 0·12 to 1·14 m^-2 and biomass from 2·56 to 25·24 g m^-2. There was no significant relationship between growth rate and density or biomass ( P > 0·05).     

Long-term study of the ecology of wild Atlantic salmon smolts in a small Norwegian river

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.     

Prey selection and functional morphology through ontogeny of Amphiprion clarkii with a congeneric comparison

The relationship between the complexity of the feeding apparatus and prey selection through ontogeny was examined in Amphiprion clarkii larvae. Larvae were reared from 1 to 10 days post-hatch (dph) on a diet of rotifers, wild-caught plankton and newly hatched Artemia sp. nauplii. Results were compared with available data on the relationship between functional morphology and prey selection of Amphiprion frenatus to establish patterns of functional morphology and prey selection between the larvae of two species of coral-reef fishes. Larvae of both species exhibited an increase in selection of larger prey through ontogeny coincident with an increase in the complexity of the feeding apparatus. The first elements to ossify in larvae of both species were the pharyngeal teeth ( A. clarkii : 5 dph, near ± s.d. Standard length, L _S,4· 3 ± 0· 2 mm; A. frenatus : 5 dph, L _S5· 0 ± 0· 4 mm) which, in combination with the development of a more functional feeding apparatus, may have permitted larvae to better process new types and sizes of prey. Prey items, however, were selected differentially between the two fish species, which could not be fully explained by the functional state of the feeding apparatus. While prey selection is influenced by the functional state of the feeding apparatus, all aspects of larval fish biology (morphology, behaviour and physiology) should be considered.