Offspring investment in wild Atlantic salmon (Salmo salar): relationships with smolt age and spawning condition

We investigated the independent effects of age at smolting and body condition at the time of spawning on egg production by female Atlantic salmon (Salmo salar). For a given body size, female salmon that had smolted as juveniles after 2 years in fresh water produced smaller, more numerous eggs than females that smolted 1 year later. Furthermore, fecundity (but not egg size) was related positively to maternal body condition at spawning. Given that age at smolting is closely related to juvenile growth rate; results from this study suggest that conditions experienced by female Atlantic salmon during both early life and adulthood have implications for the size and number of eggs that they produce.     

The influence of increased water temperature on the duration of spermatogenesis in a neotropical fish,Astyanax altiparanae (Characiformes,Characidae)

Fish Physiology and Biochemistry - In view of the established climate change scenario and the consequent changes in global temperature, it is essential to study its effects on animal...     

Life‐history variation in a species complex of nonmigratory galaxiids

Life‐history theory predicts that the optimal strategy in the trade‐off between egg size and number varies in relation to resource availability and environmental disturbance. We assessed interspecific differences in egg size, fecundity and other life‐history traits in a species complex of stream‐resident galaxiid fish, which are distributed across a range of contrasting habitat types on the South Island, New Zealand. Oocyte size, fecundity and reproductive effort were measured from gravid females collected immediately before spawning. Proxy measures of stream productivity, flow variability and predation pressure were extracted from modelled data sets. A suite of different egg sizes were identified across species within the Galaxias vulgaris complex, with mean oocyte volume differing by up to 133% between species. The species with the smallest eggs showed mean size‐relative fecundities 246% higher than the species with the largest eggs. A significant negative relationship was found between species’ mean egg size and size‐relative fecundity, suggesting a trade‐off between these traits. Species with larger eggs had larger maternal body size, lower reproductive effort and delayed maturity compared to ‘small‐egg’ species. Consistent with the predictions of life‐history theory, species with larger eggs, lower size‐relative fecundity, lower reproductive effort and delayed maturity were associated with low productivity, stable streams, whereas species exhibiting the opposite set of traits occurred in relatively productive but disturbed systems.     

The cost of early maturation on growth, body condition and somatic lipid content in a lake pumpkinseed (Lepomis gibbosus) population

We investigated the implications of early maturation in a central Ontario population of pumpkinseed (Lepomis gibbosus) by comparing the growth trajectory, body condition, lipid to body weight ratio and past growth history of mature and immature females through the 1992 growing season. Pumpkinseeds were sampled from Beloporine Lake from May 28 to July 24 and on November 20, just prior to freeze-up of the lake. Prior growth history and length at age were determined by backcalculation from scale annuli. Nearly all females age 3 and older had matured in 1992, so we focused on age 2 females (22% mature). Females that matured at age 2 were significantly larger at the end of their first year of life than those that did not mature at age 2, although there was no significant difference between groups in the prior year's growth rate. The mature age 2 females were significantly larger than immatures, at the beginning and end of their third growing season, but not during the June 2 - July 19 breeding season. The condition factor of mature females was higher than that of immature females on all but one collection date. However, the mean somatic lipid-to-body weight ratio was higher in immature females on all sample dates and significantly higher over the grwing season. We conclude that the costs of early maturation include lack of length and weight gain during the breeding season, and loss of stored lipid. The latter may be associated with increased overwinter mortality.     

Anaesthesia of Atlantic halibut (Hippoglossus hippoglossus) Effect of pre‐anaesthetic sedation,and importance of body weight and water temperature

The efficacy of the anaesthetic agents benzocaine, metacaine (MS‐222), metomidate, 2‐phenoxyethanol, quinaldine and isoeugenol was studied in Atlantic halibut (Hippoglossus hippoglossus). Fish with an average body weight of 33 g were anaesthetized at 8 °C and fish with an average body weight of 1243 g were anaesthetized at 8 and 15 °C. Agents were tested individually and as combination anaesthesia comprising pre‐anaesthetic sedation, followed by anaesthesia. Induction and recovery times varied in relation to the body weight and water temperature. Large fish had longer induction times and shorter recovery times, and displayed reduced responsiveness to handling compared with small fish. A higher temperature resulted in shorter induction times, longer recovery times and increased responsiveness to handling. Lower dosages were used for all agents in combination anaesthesia. In small fish, this had no effect on the induction times but resulted in shorter recovery times and reduced responsiveness to handling. In large fish, combination anaesthesia resulted in shorter induction times whereas no uniform trend in recovery times and no differences in responsiveness to handling were observed. Neither individual agents nor combinations blocked all reflex reactions to external stimulation in all fish of any treatment group. MS‐222 and benzocaine, used separately or in combination anaesthesia, were the most effective agents in reducing reflex reactions.     

Genetic variation and the relationship between stream and lake ecotypes of a threatened desert Catostomid,the Warner sucker (Catostomus warnerensis)

Many fish species exhibit diverse life history strategies that help maintain population viability. An understanding of the relationships among these strategies is crucial for prioritising conservation actions. The Warner sucker, endemic to the Warner Lakes Basin in southern Oregon, USA, is one example of a taxon where a lack of information regarding relationships among life history strategies has hampered conservation efforts. Warner suckers have two distinct life history types: stream‐type fish that have a fluvial life history and lake‐type fish that have an adfluvial life history. There are advantages and disadvantages associated with each life history, and presently the relationship between life history types is not well understood. Our objectives were to determine the amount of genetic variation within and among tributary populations of Warner suckers and to determine the origins of suckers collected in the Warner Lakes. We collected individuals from four tributary populations, a refugial population, and Hart and Crump lakes and genotyped them at 16 microsatellite loci. Estimates of genetic variation among populations suggested low levels of gene flow (F_ST = 0.153) and genetic variation among populations seemed to be influenced by population and habitat characteristics. Nearly all of the individuals collected in Hart and Crump lakes originated in a single tributary, Deep Creek, which likely reflects reduced habitat connectivity between most other tributaries and the Warner Lakes. Data presented in this study are useful for evaluating the status of Warner sucker populations and for prioritising conservation actions such as the removal and modification of barriers.     

Seasonal shift in spawning of Atlantic cod (Gadus morhua L.) by photoperiod manipulation: egg quality in relation to temperature and intensive larval rearing

Commercial intensive fry production of Atlantic cod will be dependent on production of viable eggs independent of season. This can only be done by manipulation of maturation by photoperiod, but little is known about potential effects on egg characteristics and larval viability. In two cod broodstocks, maturation was successfully advanced or delayed 6 months compared with normal spawning season (March–April) by manipulation of photoperiod. The advanced broodstock spawned both in spring and autumn the same year. In two of the spawning tanks during autumn, ambient temperature was reduced after reaching 13.7°C during the first half of the spawning period. Egg quality and viability were monitored, and several egg batches were incubated, hatched and start‐fed for examination of growth and survival. Temperatures above 9.6°C resulted in significant reductions in fertilization and normal egg development. Concurrently, fractions of dead and unfertilized eggs increased with elevated temperature. Actual relative fecundity was not affected by temperature. Egg characteristics improved when temperature was controlled and lowered below 9.6°C. Occurrence of irregular spawners suggests that handling of broodstock fish should be avoided during maturation and spawning. Cod larvae originating from eggs of the advanced or delayed broodstocks were successfully reared beyond metamorphosis. Survival was 9.0–46.6% and 29.3% in green and clear water respectively. Survival correlated with both initial and average feeding conditions, but growth rate did not correlate with either of survival and feeding conditions. Specific growth rates (8.3–13.6% day⁻¹) is comparable with other intensive rearing trials with cod, but were lower than reported from nature‐like systems.     

Distribution and abundance of South-west Atlantic anchovy spawners (Engraulis anchoita) in relation to oceanographic processes in the southern Brazilian shelf

The reproductive environment of the South-west Atlantic anchovy, Engraulis anchoita , in the southern Brazilian coast was investigated using maritime weather reports from the US National Climatic Center. These reports were summarized to yield seasonal distributions of sea surface temperature, wind stress and Ekman transport for 2-month segments of the seasonal cycle. The vertical oceanographic structure and dynamics were studied using temperature and salinity data collected from oceanographic cruises. The seasonal distribution and biomass of South-west Atlantic anchovy spawners were estimated by acoustic surveys. Anchoita spawns intensively off southern Brazil during winter and early spring when the Ekman transport is directed onshore, and the combined effects of freshwater run-off and the flow of cold water near the bottom result in a strong vertical stability over the continental shelf. During this season, primary production peaks due to nutrient input from Sub-Antarctic waters and freshwater run-off. These conditions would avoid dispersal of eggs and larvae offshore and favour the production and maintenance of fine-scale food particle aggregations required for successful first feeding of newly hatched larvae. In summer, the conditions are almost reversed and anchoita spawners are virtually absent from the area. Thus, the spawning strategy of anchoita in southern Brazil seems to be tuned in a way to optimize larval retention, minimize exposure to turbulent mixing and take advantage of enhanced plankton productivity.     

Distribution of albacore (Thunnus alalunga) in the Indian Ocean and its relation to environmental factors

The distribution pattern of albacore, Thunnus alalunga, in the Indian Ocean was analyzed based on catch data from the Taiwanese tuna longline fishery during the period 1979–85. The Taiwanese tuna fishery began operating in the Indian Ocean in 1967. We used a geographic information system to compile a fishery and environmental database and statistically explored the catch per unit effort (CPUE) distribution of albacore. Our results indicated that immature albacore were mainly distributed in areas south of 30°S although some displayed a north–south seasonal migration. Mature albacore, which were mainly concentrated between 10°S and 25°S, also showed a north–south migration. Within 10°S and 30°S, the separation of mature, spawning, and immature albacore life history stages roughly coincided with the boundaries of the three oceanic current systems in the Indian Ocean. The optimal environmental variables for CPUE prediction by stepwise discriminant analysis differed among life history stages. For immature albacore, the sea surface variables sea surface temperature (SST), chlorophyll concentration and surface salinity were significant. For mature albacore, SST was significant, while for spawning albacore, the sub‐surface variables temperature at 100 m and oxygen at 200 m were significant. Spawning albacore evidently prefer deep oceanographic conditions. Our results on the oceanographic conditions preferred by different developmental stages of albacore in the Indian Ocean were compatible with previous studies found in the Pacific Ocean.     

Biological traits of eastern sand darter (Ammocrypta pellucida) in the lower Thames River,Canada, with comparisons to a more southern population

Eastern sand darter (Ammocrypta pellucida) is listed as Threatened under the Canadian Species at Risk Act. Little relevant biological information is available for most Canadian populations and only limited information is available for populations in the United States. To supplement the paucity of information, this study collected biological information on eastern sand darter during field surveys in 2006–2007 from 10 sites in the lower Thames River, Ontario, Canada. Collected data were used to estimate critical life history traits including: longevity, fecundity, clutch size and number, growth, survival, age‐at‐first‐maturity and cohort age structure. Longevity was 3+ years, with age‐at‐first‐maturity being 1+ for both sexes. Examination of egg sizes from preserved females in 2007 showed a bimodal distribution, suggesting two spawning occurrences of 71 eggs each. Quantitative comparison of lower Thames River biological information with a more southerly eastern sand darter population in the Little Muskingum River, Ohio, demonstrated little variation between the populations. Data comparisons suggest that localised environmental factors are affecting biological traits (growth), in particular water temperature that may be controlled by differences in riparian cover and/or groundwater input.     

Seasonal spawning and wind‐regulated retention‐dispersal of early life stage Atlantic cod (Gadus morhua) in a Newfoundland fjord

Sequential ichthyoplankton surveys were used to determine the spatial and temporal distribution of eggs and larvae over coastal spawning grounds of Atlantic cod (Gadus morhua) in Smith Sound, Trinity Bay, Newfoundland, during the spring and summer of 2006 and 2007. Egg densities showed similar patterns for both years with two peaks in abundance in spring (March–April) and late summer (late July). A clear progression of development stages (1–4) was observed in spring and summer in 2006 and summer in 2007, suggesting retention of eggs within the Sound during these periods. Modelled predictions of vertical egg distributions indicated eggs were broadly distributed near the surface during spring (March–April), but were concentrated below the pycnocline (>10 m) within the inner portions of the Sound during the summer months (July–August). Back‐calculated peaks in spawning based on water temperatures were estimated at 11 and 4 April for 2006 and 2007, respectfully, with late season peaks centred on 21–24 July for both years. Environmental data indicated cooler water temperatures and periods of high wind stress in spring, and warmer, calmer periods late summer, consistent with higher retention and faster development times on the spawning grounds later in the season. We conclude that spring and summer spawning events result in different distributions of early life stages and may lead to different distributions of juvenile and adult fish.     

Effect of dietary protein levels on reproductive development and distribution of amino acids in the body tissues of female Pangasianodon hypophthalmus (Sauvage, 1878) broodstock in captivity

The present study investigated the optimum dietary protein level for the maturation of adult Pangasianodon hypophthalmus broodstock. Four isocaloric diets containing 250, 300, 350 and 400 g kg^?1 of protein levels were prepared and presented to triplicate groups of fish. The fish (mean weight 770 ± 17.23 g and 712 ± 23.42 g for females and males respectively) were stocked in outdoor canvas tanks (4 m × 1 m × 1 m) at a stocking density of 20 fish/tank with a male: female ratio of 1:4. The fish were fed the test diets to satiation twice daily for 6 months. Gonadosomatic index (GSI) and fecundity were similar among fish fed dietary protein levels, higher than those fed on the 250 g kg^?1. Final weight, weight gain, oocyte weight were significantly highest (P < 0.05) for the fish fed 350 and 400 g kg^?1 dietary protein treatments. Only the 350 g kg^?1 dietary protein treatment resulted in significantly best ovipositor diameter and % ripe egg. Amino acid levels were highest in the muscle followed by the oocyte and liver of fish fed 350 and 400 g kg^?1 dietary protein levels. The present results suggested that a dietary protein level of 350 g kg^?1 can be recommended for the development of P. hypophthalmus broodstock.     

Growth potential and habitat requirements of endangered age‐0 pallid sturgeon (Scaphirhynchus albus) in the Missouri River,USA, determined using a individual‐based model framework

An individual‐based model framework was used to evaluate growth potential of the federally endangered pallid sturgeon (Scaphirhynchus albus) in the Missouri River. The model, developed for age‐0 sturgeon, combines information on functional feeding response, bioenergetics and swimming ability to regulate consumption and growth within a virtual foraging arena. Empirical data on water temperature, water velocity and prey density were obtained from three sites in the Missouri River and used as inputs in the model to evaluate hypotheses concerning factors affecting pallid sturgeon growth. The model was also used to evaluate the impacts of environmental heterogeneity and water velocity on individual growth variability, foraging success and dispersal ability. Growth was simulated for a period of 100 days using 100 individuals (first feeding; 19 mm and 0.035 g) per scenario. Higher growth was shown to occur at sites where high densities of Ephemeroptera and Chironomidae larvae occurred throughout the growing season. Highly heterogeneous habitats (i.e., wide range of environmental conditions) and moderate water velocities (0.3 m/s) were also found to positively affect growth rates. The model developed here provides an important management and conservation tool for evaluating growth hypotheses and(or) identifying habitats in the Missouri River that are favourable to age‐0 pallid sturgeon growth.     

Elemental analysis of otoliths, fin rays and scales: a comparison of bony structures to provide population and life-history information for the Arctic grayling (Thymallus arcticus)

Abstract –  We used laser ablation inductively coupled plasma mass spectrometry line scans to determine the elemental composition of otoliths, pectoral fin rays and scales of Arctic grayling. Elemental signatures of otoliths and pectoral fin rays effectively provide life-history information on individual fish, important for management of grayling, and potentially all freshwater teleosts. Bulk elemental signatures measured in the otoliths and fin rays were highly correlated to the stream chemistries where the fish were captured. A surprising result of this study was that fin rays showed the strongest relationship with water chemistry for strontium. Scale strontium concentrations were not correlated to water chemistries suggesting that other physiological mechanisms, or remobilisation, may be influencing the deposition of trace elements within scales. Linear discriminant function analyses for otolith and fin ray elemental signatures (and intriguingly also for scales) separated fish from different rivers for all three structures; thus, this technique can be used effectively as a means to discriminate origin of capture.     

Carotenoid composition of a New Zealand (Evechinus chloroticus) and an Australian (Heliocidaris erythrogramma) sea urchin in relation to gonad colour

Sea urchins are commercially harvested for their edible gonads, also known as roe or uni. Most species, particularly those from the Northern hemisphere are reported to exhibit limited variation in gonad colour, which is proposed to be due to carotenoid pigments. The commercially harvested species from New Zealand, Evechinus chloroticus, and from Australia, Heliocidaris erythrogramma, however, exhibit considerable gonad colour variation, ranging from a culinary desirable light yellow/orange to an undesirable brown. Gonads from E. chloroticus and H. erythrogramma were characterized spectrophotometrically and the carotenoid content extracted and analysed by reversed‐phase high‐performance liquid chromatography. The main carotenoid found in the gonads of both species was 9′‐cis‐echinenone, with lower levels of all‐trans‐echinenone, lutein and isozeaxanthin. Carotenoid composition contributed to the yellow/orange colour components of the gonads, but was not correlated with the darker roe coloration observed in some E. chloroticus individuals. Our results highlight important considerations relating sea urchin gonad coloration to carotenoid content and as such will provide useful information for the future aquaculture and processing of these two species.     

Effects of body size and water temperature on food consumption and growth in the sea cucumber Apostichopus japonicus (Selenka) with special reference to aestivation

To investigate the effects of body size and water temperature on feeding and growth in the sea cucumber Apostichopus japonicus (Selenka), the maximum rate of food consumption in terms of energy (C_maxe; J day^?1) and the specific growth rate in terms of energy (SGRe; % day^?1) in animals of three body sizes (mean±SE) – large (134.0±3.5 g), medium (73.6±2.2 g) and small (36.5±1.2 g) – were determined at water temperatures of 10, 15, 20, 25 and 30°C. Maximum rate of food consumption in terms of energy increased and SGRe decreased with increasing body weight at 10, 15 and 20°C. This trend, however, was not apparent at 25 and 30°C, which could be influenced by aestivation. High water temperatures (above 20°C) were disadvantageous to feeding and growth of this animal; SGRe of A. japonicus during aestivation was negative. The optimum temperatures for food consumption and for growth were similar and were between 14 and 15°C, and body size seemed to have a slight effect on the optimal temperature for food consumption or growth. Because aestivation of A. japonicus was temperature dependent, the present paper also documented the threshold temperatures to aestivation as indicated by feeding cessation. Deduced from daily food consumption of individuals, the threshold temperature to aestivation for large and medium animals (73.3–139.3 g) was 24.5?25.5°C, while that for small animals (28.9–40.7 g) was between 25.5 and 30.5°C. These values are higher than previous reports; differences in sign of aestivation, experimental condition and dwelling district of test animals could be the reasons.     

Feed intake,growth and metabolism of Nile tilapia (Oreochromis niloticus) in relation to dissolved oxygen concentration

The objectives of the present study were to determine, for Nile tilapia of different body weights and fed to satiation, (1) the incipient dissolved oxygen (DO) concentration at which feed intake starts to level off and (2) the effect of DO on nitrogen and energy balances. Two successive experiments were conducted with two weight classes of male Nile tilapia (>200 g, Experiment 1, and <100 g, Experiment 2). Twelve aquaria were assigned to four DO levels in each experiment. Fish were fed to apparent satiation for 16 and 20 days in Experiments 1 and 2 respectively. The DO‐feed intake curve of fish<100 g appeared to level off at a DO of 3 mg L^?1, while that of fish>200 g continued to increase as DO increased from 2.6 to 6.0 mg L^?1. The latter curve suggests that the incipient DO for fish>200 g is about 5.5 mg L^?1. Fish tended to reduce the energy requirement for maintenance as DO declined. A DO reduction caused an increase in the apparent digestibility coefficient (ADC), but further declines in DO to levels below a critical level decreased ADC. The DO did not have a considerable effect on the metabolizable energy: digestible energy ratio of the diet.     

Size,permeability and buoyancy of anchovy (Engraulis Encrasicolus) and sardine (Sardina Pilchardus) eggs in relation to their physical environment in the Bay of Biscay

The size and specific gravity of eggs of marine pelagic fish partly determine their dispersal and survival. Using an original dataset of anchovy and sardine eggs, sampled in spring over the last decade in the Bay of Biscay, we provide a parameterization of these properties on ambient water temperature and salinity. We used the density gradient column for measurement of egg specific gravity. The column was also filled with homogeneous water for sinking velocity experiments. For anchovy, these experiments confirm that the effect of egg permeability through the chorion could be neglected when modelling sinking, while it has to be considered for sardine, its perivitelline space representing 78.6% (±6.2%) of the total egg volume, as opposed to 5–10% for most teleosts species. We estimated a coefficient of permeability of the chorion of 0.0038 mm s^?1. However, permeability should not affect the measurement of sardine egg specific gravity in a gradient column, provided a minimum duration before reading is respected for equilibrium to be reached. In relation to their environment, we found that the egg specific gravity is largely determined by sea surface salinity for both species, whereas egg size is weakly but significantly impacted by temperature, for sardine only. On average, the estimated difference in specific gravity between egg and surface water is ?0.92 σ_T for anchovy and ?1.06 σ_T for sardine. The detailed parameterization of the relationship between eggs and water properties should prove useful, in particular to modellers dealing with the dispersal of fish early life stages.     

Reproductive success of the Argentine anchovy,Engraulis anchoita,in relation to environmental variability at a mid‐shelf front (Southwestern Atlantic Ocean)

The mid‐shelf front (MSF) of the Buenos Aires province continental shelf in the Southwestern Atlantic Ocean plays a central role in the pelagic ecosystem of the region acting as the main spring reproductive area for the northern population of the Argentine anchovy Engraulis anchoita and supporting high concentrations of chlorophyll as well as zooplankton, the main food of anchovy. To investigate the influence of environmental variability on the reproductive success of E. anchoita, we analyzed a 13‐yr time series (1997–2009) of environmental data at MSF including chlorophyll dynamics, as well as zooplankton composition and abundance, ichthyoplankton distributions, and recruitment of E. anchoita. Spring chlorophyll concentrations showed high interannual variability and were mainly influenced by changes in water temperature and vertical stratification, which in turn control nutrient supply to the surface. Chlorophyll dynamics (magnitude, timing, and duration of the spring bloom) explained most of the variability observed in E. anchoita recruitment, most likely via fluctuations in the availability of adequate food for the larvae. Our results suggest that satellite ocean color products can be valuable tools for understanding variability in ecosystem dynamics and its effects on the recruitment of fish.     

Effect of dietary fish and vegetable oil on the growth performance,body composition,fatty acids profile,reproductive performance and larval resistance in pearl gourami (Trichogaster leeri)

This study investigated the effect of two lipid sources on reproduction performance and growth in pearl gourami. For this purpose, 180 fish (3.32 ± 0.25 g) were fed with three isoenergetic (19.80) and isonitrogenous diets (480 g/kg protein) including FO (80 g/kg fish oil), FS (40 g/kg fish oil and 40 g/kg soybean oil) and SO (80 g/kg soybean oil) for 10 weeks before maturation. At the end of the trial, there was no significant difference in weight gain, feed conversation ratio and body composition between fish fed FO and FS diets. Individuals fed dietary FO had significantly higher levels of n‐3 long‐chain polyunsaturated fatty acids in the muscle (130.5 g/kg lipid) and ovary (140.4 g/kg lipid) as compared with those fed SO diet (64.5, 103.6 g/kg, respectively) (p < .05). Feeding pearl gourami with FO and FS diets enhanced regarding absolute fecundity, relative fecundity, the fertilization rate, larvae total length and survival at 3 day posthatch (p < .05). Also, 17 beta‐estradiol in plasma of fish fed dietary FO (6.2 ng/L) was higher than those fed SO diet (1.7 ng/L) (p < .05). In conclusion, we suggest FS diet for broodstock nutrition of pearl gourami as a model for asynchronous multi‐batch spawning fish.