Interindividual variations in feeding and growth in rainbow trout during restricted feeding and in a subsequent period of compensatory growth

Compensatory growth responses of rainbow trout Oncorhynchus mykiss were studied by examining food intake and growth of individual fish held within groups that were switched between regimes that involved full and restricted feeding. Restricted feeding led to marked interindividual variability in food intake, probably as a result of the establishment of feeding hierarchies. This disparity in food acquisition was reflected in highly heterogeneous growth amongst the fish fed low rations. When fish were transferred from restricted to full rations, they became hyperphagic and displayed high rates of growth. Growth compensation was most marked amongst those fish which had shown the poorest growth during the period of feed restriction. These results suggest that the feeding hierarchies established under feed restriction did not persist, but were rapidly broken down when food became increasingly available, enabling the previously suppressed fish to gain access to food and to display rapid growth.     

Growth and mortality of Arctic charr and European whitefish reared at low temperatures

This comparative study explores how low temperatures affect the mortality and growth of first generation hatchery-reared progeny of subarctic populations of Arctic charr (Salvelinus alpinus L.) and European whitefish (Coregonus lavaretus L.). Replicate fish groups where held under simulated natural light regimes (70°N) at three constant temperatures (1, 3 and 6°C). The mortality of Arctic charr was low (≤1.4%) at all temperature treatments, whereas the mortality of whitefish increased with decreasing temperature from 6% at 6°C to 33% at 1°C. The Arctic charr exhibited higher growth rates than whitefish at all three temperature regimes. All groups of Arctic charr increased in weight, whereas whitefish held at 1°C did not gain weight throughout the experimental period of 133 days. Arctic charr exhibited a large intraspecific variability in growth leading to large variations in size-structure, whereas whitefish in contrast showed very homogenous growth and size-structure patterns; a dissimilarity probably related to species-specific differences in antagonistic behaviour. Evidently, Arctic charr are more cold water adapted than whitefish and are able to maintain growth at extremely low temperatures. Arctic charr thus appear to be the most suitable species for aquaculture at low water temperatures.     

Variations in feed intake and growth of Baltic salmon and brown trout exposed to continuous light at constant low temperatures

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.     

A comparison of growth patterns between a stunted and two large predatory Arctic charr populations under identical hatchery conditions

Arctic charr are characterized by an extensive variability in growth and body size in natural waters. Although growth traits may involve a significant heritable component, most of this intraspecific variation presumably is environmentally induced and thus attributable to phenotypic plasticity. In the present study, size-at-age and length–weight relationship (body condition) were assessed for three Finnish Arctic charr populations of different geographical origins and extreme size forms (a stunted vs. two large-growing, predatory charr) held under standardized rearing conditions for 3 years (up to 37 months after hatching). In particular, our interest was to investigate whether the differences in growth between the large and the stunted charr as observed in the wild populations would diminish when the fish are offered suitable food in abundance. Population-specific mean body size and condition differed significantly in 0+, 1+, 2+ and 3+ fish. However, the identical rearing conditions resulted in the originally stunted charr reaching a comparable final mean size (317 mm/427 g) as the large charr populations (343 mm/510 g and 359 mm/497 g). Some individuals were of the same size as their parents at spawning already at the age of 0+ years. Furthermore, length–weight regression residuals of the stunted charr developed to a notably high level, indicating the largest final condition mean. The increase of size variation (CV of weight) in stunted charr lasted for over two growth seasons, whereas in large charr it remained stable since the end of the first summer. Variations in mortality and sexual maturation at age 2 seemed to be less relevant factors affecting overall growth performance. The study demonstrates an example of the high plasticity involved in the growth of fish: the stunted charr possess a tremendous capacity for growth in a benign environment, virtually corresponding to that observed in the large predatory populations.     

Intraspecific competition and density dependence of food consumption and growth in Arctic charr

1. Intraspecific competition for restricted food resources is considered to play a fundamental part in density dependence of somatic growth and other population characteristics, but studies simultaneously addressing the interrelationships between population density, food acquisition and somatic growth have been missing. 2. We explored the food consumption and individual growth rates of Arctic charr Salvelinus alpinus in a long-term survey following a large-scale density manipulation experiment in a subarctic lake. 3. Prior to the initiation of the experiment, the population density was high and the somatic growth rates low, revealing a severely overcrowded and stunted fish population. 4. During the 6-year period of stock depletion the population density of Arctic charr was reduced with about 75%, resulting in an almost twofold increase in food consumption rates and enhanced individual growth rates of the fish. 5. Over the decade following the density manipulation experiment, the population density gradually rose to intermediate levels, accompanied by corresponding reductions in food consumption and somatic growth rates. 6. The study revealed negative relationships with population density for both food consumption and individual growth rates, reflecting a strong positive correlation between quantitative food intake and somatic growth rates. 7. Both the growth and consumption rate relationships with population density were well described by negative power curves, suggesting that large density perturbations are necessary to induce improved feeding conditions and growth rates in stunted fish populations. 8. The findings demonstrate that quantitative food consumption represents the connective link between population density and individual growth rates, apparently being highly influenced by intraspecific competition for limited resources.     

Influence of body weight and temperature on growth rates of Arctic charr, Salvelinus alpinus (L.)

When reared for a period of 6 months at a temperature of 10°C Arctic charr, Salvelinus alpinus , increased in weight from 18 g to approximately 135 g. Specific growth rates decreased as the fish increased in size and the relationship between size and growth rate could be described by the equation:
where G _w is specific growth rate and W is fish weight in grams. Temperature effects upon growth were examined using previously published data. Below the optimum growth temperature, the growth rate of a fish of given size could be predicted using the equation:
where T is the rearing temperature.
Rates of growth of Arctic charr were as high as those reported for other salmonid species reared under similar conditions. Preliminary results suggested that growth rates of charr may be lower in salt water than in fresh water.     

Seasonal changes in food consumption and growth of Arctic charr exposed to either simulated natural or a 12:12 LD photoperiod at constant water temperature

Immature male and female and maturing male Arctic charr Salvelinus alpinus were held at constant temperature (4° C) under either simulated natural photoperiod (nLD) or constant photoperiod (12:12 LD) conditions, and feed intake and growth were monitored at monthly intervals over 13 months. Food was supplied in excess during a 5-h period each day, and daily consumption was determined using X-radiography. Food consumption and growth of both immature and maturing fish showed distinct seasonal cycles irrespective of photoperiod treatment. Feed intake and growth rates were highest in mid-summer and lowest in autumn. The fact that seasonal cycles persisted under constant photoperiod (12:12 LD) and temperature conditions suggests that circannual rhythms of food consumption and growth exist in the absence of seasonal changes in these environmental cues. The data support the view that seasonal changes in food consumption and growth in the Arctic charr are driven by endogenous rhythms. Reductions in feeding and growth in autumn occurred about 1 month earlier in the maturing males than in the immature fish. Males that matured under the 12:12 LD regime displayed a growth cycle that was delayed in comparison with that shown by the maturing males held under nLD.     

Growth heterogeneity in rearing sea bass ( Dicentrarchus labrax): test of hypothesis with an iterative energetic model

This study aimed at modeling the relative importance of food intake on growth heterogeneity among cultured sea bass (Dicentrarchus labrax). First, we designed an individual growth model comprising five compartments (Energy intake, Losses, Net Energy, Recovered Energy and Maintenance). This model was calibrated with a first experiment carried out in eight tanks; A total of 130 juveniles (11 g) per tank were fed by a self-feeder (84 days, 20°C, 16L : 8D, 30 g NaCl/l). A second experiment was performed to better understand the relation between individual food intake, individual growth and growth heterogeneity, using the model as a tool for a hypothetico-deductive approach on growth heterogeneity (135 passive integrated transponder-tagged fish, same rearing conditions as above and individual food intake measured by X-ray every 14 days). The tested hypotheses were that food intake was (a) homogeneous, (b) proportional to the fish weight (i.e. to W1.00) X-ray (c) proportional to W0.66 and (d) reflected by the X-ray measurements of food intake. For each hypothesis, a simple linear regression between experimental and simulated results was produced. The Fitness indicators of these analyses, together with their confidence intervals (calculated by bootstrapping), allowed testing the relevance of these hypotheses. The analysis indicated that growth heterogeneity was largely accounted for by individual variations of food intake, as revealed by the X-ray analysis, and that food intake was proportional to W1.00, which suggests a dominance hierarchy where small fish are incapable of feeding maximally.     

Physiological and social constraints on growth of Arctic charr, Salvelinus alpinus L.: an investigation of factors leading to stunting

When stunted (runt) Arctic charr, Salvelinus alpinus , were reared together in small groups growth rates were low. Contrary to expectation, there did not arise a rapidly growing despot within each group. It is suggested that the narrow size range offish within groups prevented the rapid formation of clear-cut dominance hierarchies. Fish reared in isolation had significantly higher and more variable rates of growth than those held in groups, demonstrating that social interactions between individuals were responsible for growth suppression of grouped-reared fish. There were no significant differences in growth rates between fish allowed visual contact with conspecifics and those held in visual isolation, indicating that visual contact is insufficient to cause growth depensation in Arctic charr. Despite the fact that growth rates of stunted (runt) Arctic charr improved when they were held in isolation, the growth rates recorded were substantially lower than those of normal individuals reared under hatchery conditions. It is concluded that physiological (genetic) factors are important in the determination of the slow growth rates of stunted (runt) Arctic charr and that this trend is exacerbated by social interactions with more rapidly growing siblings.     

Stable isotope-based determinations of the average temperatures experienced by young-of-the-year Svalbard Arctic charr (Salvelinus alpinus (L.))

Mean ambient water temperatures experienced by individual young-of-the-year (YOY) Arctic charr, Salvelinus alpinus (L.), from a Svalbard lake were estimated using measurements of oxygen stable isotopes (δ¹⁸O) derived from fish otoliths. Otolith-derived water temperatures differed significantly from temperatures recorded at the outlet river of the Dieset watercourse but were consistent with temperatures previously recorded in shallow littoral areas of other Svalbard lakes where YOY charr are commonly found. This indicates that fixed-point monitoring does not necessarily represent the temperatures and thermal habitats used by individual fish. Otolith-derived water temperatures were also positively related to fish length-at-capture and otolith size, although much of the variation remained unexplained. Differences among individuals could be related to variability in food availability and food intake as well as variation in the initial fish size at hatching. Implications for subsequent investigations into how YOY charr respond and adapt to future climate change are discussed.     

The influence of food distribution upon the development of aggressive and competitive behaviour in juvenile chum salmon, Oncorhynchus keta

Groups of juvenile chum salmon were reared on food that was either dispersed throughout, or localized in one area of, the rearing tank. Groups receiving localized food displayed more aggression than those receiving dispersed food. This led to differences in growth, with fish reared on localized food having greater individual growth variability, i.e. growth depensation. However, after several months of rearing in these different feeding/social environments, fish reared on dispersed food were just as aggressive when first exposed to localized food as were fish reared on localized food. Furthermore, in competitive contests between fish of the two rearing histories, those reared on dispersed food were just as likely to become dominant as those reared on localized food. These results suggest that the behavioural development of aggressiveness is not amenable to alteration by manipulation of food distribution.     

Observations on growth rates of Arctic charr, Salvelinus alpinus (L.), reared at low temperature

Food intake and growth of Arctic charr, Salvelinus alpinus , in fresh water was studied at three temperatures 2·9, 8·4 and 13·1° C). Best growth and highest food intake occurred at 13·1°C. The approximate chemical composition was dependent upon rearing temperature, fish reared at the highest temperature depositing large quantities of fat. Fish were later grown on in either fresh or salt water where two growth patterns were observed. In the light of published data for Salvelinus spp., it is suggested that the poorest growth was shown by fish which were incapable of complete adaptation to saltwater conditions.     

Methods for assessing social status in Arctic charr

The aggression index is a more reliable method for assessing the social status of Arctic charr Salvelinus alpinus held in small groups, than is food intake or position relative to a defensible food resource. However, care must be taken when assigning rank, as all three of these commonly used methods can result in different social ranks for an individual fish.     

Genetic basis of life-history variation of dwarf and normal Arctic charr,Salvelinus alpinus (L.), in Stora Rösjön,central Sweden*

The genetic basis of life-history variation of dwarf and normal Arctic charr forms in Stora Rosjon was studied by means of two separate rearing experiments on the progeny of artificially bred wild fish. The concept of differential life-strategies gained support, since the progeny of the normal charr form had a higher growth rate and became sexually mature at a larger size and later age than the progeny of the dwarf charr form. The hybrid progeny (dwarf × normal parental charr) was recognized as intermediate in growth as well as in size and age at maturity, compared to the normal and dwarf progeny. However, a dominance effect of the growth and maturation pattern of the dwarf charr was revealed, since hybrid progeny were more similar to dwarf than to normal progeny. The rearing experiments also support the view that the dwarf and normal charr forms are inherited characteristics of one population, since any individual progeny cannot be assigned to a certain form according to its size and age at maturity.     

Daily rations,diel feeding activity and distribution of age-0 brook charr,Salvelinus fontinalis,in two subarctic streams

Synopsis Diel variations in the stomach content weight of age-0 brook charr indicate that they fed primarily during the day in Matamek River and Rivière à la Truite, Québec. Age-0 charr in both rivers moved close to the shore at night. The mean weight of stomach contents in Rivière à la Truite was highest at the end of the daylight period, whereas in the Matamek River stomach content weights maintained maximum level during most of the day, except in August when high water temperatures reduced food intake. Daily rations were estimated at 5.09 and 4.09% body weight for charr from Rivière à la Truite in July and August, respectively. In the Matamek River, estimates were 7.13, 9.75, and 1.27%, in June, July, and August, respectively. Charr from Matamek River had a higher instantaneous growth rate than charr in Rivière à la Truite (3.96 versus 2.72% body weight per day) and were significantly heavier by mid-August. Differences observed between populations in daily rations and growth rates were attributed mainly to differences in water temperature regimes.     

Vaccination influences growth of Arctic charr

There is limited knowledge about the effects of oil-based vaccines on the growth of Arctic charr Salvelinus alpinus, in particular at different rearing temperatures. One-year-old Arctic charr were immunized intraperitoneally at 2.9 degrees C with a metabolizable oil-adjuvanted, bivalent vaccine containing killed typical and atypical Aeromonas salmonicida bacteria. After vaccination the non-vaccinated (controls) and vaccinated individually marked fish were held for 20 d at 10.0 degrees C and then for 7 wk at 10.3, 14.1 or 18.1 degrees C. During the first 20 d at 10.0 degrees C the growth rate (G) was higher for non-vaccinated than vaccinated fish. Thereafter vaccinated charr had higher G than control fish at 10.3 and 14.1 degrees C. In contrast, at 18.1 degrees C there was no difference in G and therefore no compensation of earlier growth suppression in vaccinated fish was observed at that temperature. The study indicates that vaccination has no ultimate negative effects on the growth of Arctic charr at temperatures ranging from 10.3 to 14.1 degrees C.     

Individual variation in distribution, activity and growth rate of Arctic charr kept in a three-tank system

The movements and distribution of groups of Arctic charr Salvelinus alpinus were examined in a rearing system that offered a choice between two different feeding tanks separated by a larger non-feeding tank. The passages of individual fish were monitored continuously during a period of 3 weeks using the PIT (passive integrated transponder)-tag technique. The primary aim was to examine if only some charr were occupying the feeding tanks, thereby excluding other individuals, and whether differences in visit activity explained within-group variation in individual growth. On average, about 35 of the 40 charr in each group shoaled in the large non-feeding tank leaving only five individuals in the feeding tanks. Charr that spent a long total time in one of the feeding tanks made frequent excursions to the other tanks resulting in a continuous exchange of individuals. Individual growth rates were correlated positively with visit activity rather than with the total time spent in the feeding tanks. Thus, individuals with low growth rate spent as much time in feeding tanks as charr with high growth rate. However, less successful fish tended to visit the feeding tanks at night when the feeders were switched off. Based on behavioural and growth results obtained in this experiment, the use of multitank systems in the cultivation of Arctic charr is discussed.     

Influence of maturity status on the annual cycles of feeding and growth in Arctic charr reared at constant temperature

Temporal changes in feeding and growth of immature (1 +), maturing male (1 +), and mature male and female (3+) Arctic charr were studied by monitoring feed intake and growth of individually-marked fish for over 1 year. The fish were held at a constant temperature (4°C) under conditions of liberal feed supply. Feed intake and growth remained low in the period December-April, with only 20–60% of the fish having fed on each occasion that feed intake was monitored. Feed intake and growth increased markedly during the late spring and summer, but the increases were delayed by approximately 1–2 months in the immature fish compared with their maturing counterparts. Maturing fish decreased feeding during the late summer and by September there had been an almost complete cessation of feeding. This was reflected in changes in fish body weight and condition, both of which declined from August-September onwards. By contrast, the immature fish peaked in weight and condition in September, and weight loss during the autumn tended to be less rapid than observed for the maturing fish. The fish appeared to reduce feeding once a'threshold condition' of 1–4—1–5 had been attained. It is suggested that the fish may become anorexic once there has been replenishment of the energy reserves required for overwintering and, in the case of maturing individuals, for the completion of gonadal growth and Spawning.     

State-dependent feed acquisition among two strains of hatchery-reared Arctic charr

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.     

Cyclic growth and activity of pancreatic enzymes in alevins of Arctic charr (Salvelinus alpinus L.)

Growth and digestive enzymes were studied in alevins of Arctic charr raised on six commercial diets that differed in protein source and level. There were links between diet composition (protein quality), fish performance and proteolytic and amylase enzyme activities. Trypsin and amylase activities were up to 10-fold higher in charr fed high protein (65–70%) diets than in fish fed live feed. A depression of pancreaticenzyme activities was noticeable when charr were fed starter diets in which fish meal was partially replaced by soybean meal. Specific growth rates (SGR) showed a cyclic pattern during early ontogeny of charr and SGR was highly correlated with food conversion efficiency. Activities of pancreatic enzymes also demonstrated a cyclic pattern but the periodicities of the growth cycle (50.6 days) and those of the enzymes differed. We hypothesize that both photostimulation and feedback responses might be involved in pancreatic responses in fish, which result in cyclic growth patterns.