Effects of Group Membership and Size Distribution within a Group on Growth Rates of Juvenile Sablefish Anoplopoma fimbria

Group membership can confer both advantages and disadvantages to growth in juvenile fishes. The balance between costs and benefits of social interactions can shift depending on such factors as the composition of the group (density and size disparity) and the availability of food. We examined the effect of these factors on absolute growth and growth depensation in juvenile sablefish, Anoplopoma fimbria. Increasing density and increasing size disparity had little influence on absolute growth rates of juvenile sablefish and the effects of these social factors were not modified by ration level. In experiments testing density effects, absolute growth did not differ among groups of 1, 3, or 10 fish held at high rations, but at low rations single fish exhibited a different pattern of size-dependent growth compared to fish in groups. In experiments testing disparity effects, absolute growth did not differ between groups with an even size distribution and groups with a mixed size distribution. The relative size of an individual within a group, i.e., small, medium, or large, also did not modify growth, despite evidence of higher chasing behavior in mixed size distributions. Although the growth of small fish was not diminished in the presence of large fish, negative impacts of size disparity were expressed in high levels of cannibalism, which occurred in 42% of groups with a mixed size distribution. Significant growth depensation over time occurred in the density experiment, but not in the size disparity experiment, possibly due to the shorter duration of the latter experiment. We suggest that growth depensation was generated by individual variability in growth capacity rather than social effects on growth rates. Schooling behavior, measured by group cohesion indices, increased with fish size and was higher in groups with an even vs. a mixed size distribution. These results for sablefish are consistent with other schooling species in which growth variability is determined by exploitative competition and/or genetic variability in growth capacity rather than interference competition.     

Effect of ration and body size on the energy budget of juvenile white sturgeon

Growth and energy budget were measured for three sizes (2.4, 11.1 and 22.5 g) of juvenile white sturgeon Acipenser transmontanus held at 18.5° C and fed tubificid worms at different levels ranging from starvation to ad libitum . For each size-class, specific growth rate increased linearly with increasing ration, and conversion efficiency was highest at the maximum ration. Growth rate decreased with increasing fish size at the maximum ration, but increased with size at each restricted ration. Conversion efficiency increased with increasing ration for each size-class and was usually highest at the maximum ration. Faecal production accounted for 3.2–5.2% of food energy. The proportion of food energy lost in nitrogenous excretion decreased with increasing ration. With increases in ration, the allocation of metabolizable energy to metabolism decreased, while that to growth increased. Fish size had no significant effect on the allocation of metabolizable energy to metabolism or growth. At the maximum ration, on average 64.9% of metabolizable energy was spent on metabolism, and 35.1% on growth.     

Energy allocation in juvenile sablefish: effects of temperature, ration and body size

The lipid deposition of juvenile sablefish Anoplopoma fimbria was examined, in particular, the changes in allocation over time. Growth rates of early juveniles (initial size 36–50 mm total length, L_T) were manipulated using two temperatures (10 and 20° C) and two rations (ad libitum and 3–4% body mass day^?1). Fish L_T, mass and lipid content were measured every 3 weeks for 15 weeks. Irrespective of treatment, the relationship of total lipid content with body size was clearly hyperallometric; small juveniles allocated relatively more energy to growth and less to lipid storage than large juveniles. After adjusting for the influence of body size, temperature and ration significantly influenced body composition but these effects varied over the course of the experiment. In the first 3 week time period, fish on the high ration, high temperature treatment had reduced lipid storage relative to other treatments, but in all subsequent time periods their lipid concentrations were similar to or higher than those of fish on other treatments. In contrast, fish held at low rations and low temperatures initially had average levels of lipid concentration, but after 6 weeks their levels were lower than other treatments. Estimation of allocation to lipid storage over time (proportion of dry mass increase comprised of lipid) suggested that fish in all of the treatments were approaching an asymptotic level of lipid concentration (c. 50–60% of dry mass) but with different rates of lipid increase. Within a treatment, it was predicted that individual differences in allocation would result in trade‐offs between somatic growth and storage. This trade‐off was evident only for fish held on low rations at low temperatures. In contrast, fish held on high rations at high temperatures exhibited the opposite pattern of a positive correlation between somatic growth and storage. These results suggest that lipostatic regulation of appetite is unlikely in juvenile sablefish. When resources are unlimited, this species appears to adopt a maximizing strategy for both somatic growth and lipid accumulation.     

Effect of ration size and feeding frequency on growth, size distribution and survival of juvenile clownfish, Amphiprion percula

This study describes the growth of juvenile clownfish, Amphiprion percula Lacépède 1802, fed with an artificial diet at six ration sizes of 2, 4, 6, 8, 10 and 12% of body mass per day (BM day^?1) each at a feeding frequency of once, twice and three times per day. The effect of ration size on growth depended on the feeding frequency. In fish fed once a day growth did not improve above a ration size of 8% BM day^?1. At two feedings per day fish required a ration size of at least 6% BM day^?1 to achieve good growth, and fish fed three times per day grew at similar rates above a ration size of 4% BM day^?1. A model to estimate the combined effect of ration size and feeding frequency is presented. The results lead to the suggestion of a simple length‐based feeding regimen that could be tested in future studies on this species or adapted for use in other species.     

Effects of fish size and ration level on the growth and food conversion efficiency of rainbow trout, Salmo gairdneri Richardson

The growth rates of rainbow trout, Salmo gairdneri , which ranged in size from 0.6 to 5.2 g and were provided rations of three different sizes, were measured during a 15-day study. The relative maintenance rations (food/gram of fish at zero growth rate) decreased with increases of fish size. Consequently when fish were kept at low ration levels the growth rates and gross efficiencies of food conversion of 'large' fish were greater than those of 'small' fish. However, as ration level increased, the effects of fish size grew at the same rates or slower than small fish. With increases of ration to the highest levels (9–12%/day) gross efficiency values for large fish began to decline while those for small fish continued to increase.     

Size dominance affecting the social interactions and growth of juvenile Japanese flounder,Paralichthys olivaceus

Juvenile flounder Paralichthys olivaceus were size‐graded into three groups (small, large and mixing of small and large) and social interactions (feeding, aggressive attacking and activity) and growth of the fish were investigated. Growth of the subordinates (small flounder) was markedly suppressed by the presence of the dominants (large flounder). Dominants did not significantly suppress the overall food intake of the subordinates, but exhibited high aggressive attacking on the subordinates and consequently inhibited their activity. Size dominant interactions had little influence on the aggressive behaviour, feeding, activity and growth of the dominants. Results substantiated the hypothesis that the retardation in the growth of the subordinate flounder was attributed to the physiological costs of ‘stress’ by the aggression of the dominants. Individual differences in aggressive behaviour, feeding and activity were at least partly responsible for the growth depensation of the juvenile flounder. The dominants could not effectively defend the food in excess and disproportional food acquisition of the subordinates and dominants was not the primary mechanism responsible for the size hierarchy effect. In culture, size grading of the early juvenile flounder could markedly improve the growth and survival and thus possibly increase the overall biomass production of the flounder.     

Function and variability of male sex traits in a blenniid fish, Parablennius tentacularis

Juvenile flounder Paralichthys olivaceus were size‐graded into three groups (small, large and mixing of small and large) and social interactions (feeding, aggressive attacking and activity) and growth of the fish were investigated. Growth of the subordinates (small flounder) was markedly suppressed by the presence of the dominants (large flounder). Dominants did not significantly suppress the overall food intake of the subordinates, but exhibited high aggressive attacking on the subordinates and consequently inhibited their activity. Size dominant interactions had little influence on the aggressive behaviour, feeding, activity and growth of the dominants. Results substantiated the hypothesis that the retardation in the growth of the subordinate flounder was attributed to the physiological costs of 'stress' by the aggression of the dominants. Individual differences in aggressive behaviour, feeding and activity were at least partly responsible for the growth depensation of the juvenile flounder. The dominants could not effectively defend the food in excess and disproportional food acquisition of the subordinates and dominants was not the primary mechanism responsible for the size hierarchy effect. In culture, size grading of the early juvenile flounder could markedly improve the growth and survival and thus possibly increase the overall biomass production of the flounder.     

Morphological limitations, prey size selectivity, and growth response of juvenile atlantic salmon, Salmo salar

The head and jaw movements involved in capture, buccal manipulation, ingestion and rejection of prey were investigated using sequential photography of juvenile Atlantic salmon feeding in a simulated stream environment. The results are described and discussed and mouth breadth and gill raker spacing are proposed as morphometric limitations to the range of prey sizes available which remains constant at 0·06 · fish fork length ( PFR ).
A recirculatory flume tank was used to study prey size selectivity behavior. Simplified downstream-drifting prey items elicited a variety of responses depending on their physical size. One hundred percent of offered prey of PFR 0·025 were ingested, while 90 % of prey at PFR 0·051 and 100% of prey at PFR 0·105 were rejected. It is demonstrated that fish show negative selection for prey sizes smaller than PFR 0·025 and that prey of this size elicits maximum growth response.
The validity of the proposed morphometric limitations on the available prey sizes is demonstrated by reference to selectivity behaviour and prey size related differential growth.     

Tissue essential fatty acid composition and competitive response to dietary manipulations in white bass (Morone chrysops), striped bass (M. saxatilis) and hybrid striped bass (M. chrysopsxM. saxatilis)

The effects of wide changes in dietary levels of docosahexaenoic (DHA) or arachidonic (ArA) acids on growth, survival and fatty acid composition in body tissues of Morone larvae were examined. White bass (WB, Morone chrysops), striped bass (SB, Morone saxatilis) and sunshine hybrid bass (HSB, M. chrysopsxM. saxatilis) larvae (day 24-46) were fed Artemia nauplii enriched with algal sources of varying proportions of DHA and ArA (from 0 to over 20% of total fatty acids). WB larvae fed DHA-deficient Artemia diet retarded over 50% of their potential growth, however, increasing dietary DHA/ArA ratios were associated with a significant growth improvement. The highest proportion of polyunsaturated fatty acids was found in WB neural tissue (approx. 50% of total fatty acids), while HSB neural tissue contained the highest proportion of saturated fatty acids (approx. 35% of total fatty acids). Within the neural tissues of all Morone larvae, both DHA and ArA were generally the most dominant as well as the most responding fatty acids to dietary manipulations (except in WB fed DHA or ArA deficient diets). HSB neural tissue was particularly efficient in retaining a significant amount of DHA in the face of dietary deficiency. However, WB neural tissue was the most responsive to dietary increase in DHA, accumulating a significantly higher amount of DHA (P<0.05) than SB or HSB. Results demonstrate significant differences in fatty acid composition and growth responsiveness to dietary manipulations between Morone larvae species and within specific tissues. WB weight gain and neural tissue composition was affected most by dietary changes in both DHA and ArA whereas SB and HSB tissue compositions were generally less affected by dietary manipulations.     

Growth depensation and aggression in laboratory reared coho salmon: the effect of food distribution and ration size

Groups of recently emerged coho salmon fry Oncorhynchus kisutch were reared for 3 months on food that appeared either asynchronously at a single location (localized) or synchronously and spatially dispersed (dispersed). Groups were further subdivided into those receiving low (1%) or high (3% body weight per day) rations, with five replicate groups for each treatment combination. At low ration there was greater growth depensation, i.e. growth variation, in groups receiving localized as compared to dispersed food. At high ration there was no difference. There was no effect of food distribution upon mean fish weight, but groups receiving high rations had greater mean fish weights than groups receiving low rations. There was no overall difference in the frequency of chasing between any of the treatment combinations. However, in localized food groups, dominants defended positions close to where food entered the tank, giving them greater access than subordinates. In dispersed food groups, while dominants also defended particular areas, this did not result in greater access to food. These results demonstrate that although feeding methodology may not directly influence the frequency of aggressive interactions, feeding methods which facilitate food monopolization by dominants can accelerate the growth of these individuals at the expense of subordinates. In aquacultural applications where greater size is desirable, or otherwise selected for, this may result in the unintentional selection for increased aggressiveness.     

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.     

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.     

Growth and the size hierarchy effect: an experimental assessment of three proposed mechanisms; activity differences,disproportional food acquisition,physiological stress

Synopsis Juvenile cichlids, Tilapia zillii, of equal initial standard length were randomly assigned to one of five treatments to assess the relative importance of individual physiological and activity differences, disproportional food consumption, and social interaction on growth depensation and mean growth. Results substantiate the hypothesis that disproportional food acquisition is the primary mechanism responsible for the size hierarchy effect. Individual physiological and activity differences played a negligible role in the phenomenon. Dominant-subordinate relationships, set up in the aquarium, appear responsible for the disproportional food acquisition and thus mediate the size hierarchy effect. Dominant fish ingest more food by either acquiring a limited ration first, preventing a subordinate's food acquisition, or behaviorally inhibiting a subordinate's feeding behavior.     

Energy and ration requirements of juvenile Pacific halibut (Hippoglossus stenolepis) based on energy consumption and growth rates

Growth of captive juvenile Pacific halibut was linearly related to energy consumption (J g⁻¹ day⁻¹) at 4°C by the following equation: growth (% body weight (b.w.) day⁻¹)=0–007 (consumption J g⁻¹ day⁻¹)– 0.192; r² =0.81. Weight gain was independent of size for fish between 9 and 7000 g when growth was expressed as a function of consumption in J g⁻¹ day⁻¹. Maintenance ration determined in feeding–growth experiments averaged 27.4 J g⁻¹ day⁻¹ at 4–0°C. Small halibut ate significantly more food than large fish. Single meals following 2 day fasts averaged 4.1% b.w. for halibut under 100 g, 1.72% b.w. for 1.2 kg fish and 1.1% B.W. for 6.8 kg fish. Both large and small size categories of halibut tended to evacuate their meal in about 3 days even though small fish ate relatively larger meals. Minimum estimates for daily ration to achieve growth rates observed in the Gulf of Alaska were approximately 0.5 to 2.4% b.w. day⁻¹ depending on fish size and whether northern shrimp or yellowfin sole were their prey.     

Fillet yield and chemical composition of farm-raised sunshine bass (Morone chrysops♀ × Morone saxatilis♂) fed high-energy diets

Fillet yield and chemical composition were evaluated in small, medium and large (about 150, 350 and 700 g, respectively) size classes of sunshine bass ( Morone chrysops ♀ ×  Morone saxatilis ♂) fed high-energy diets. Fish size had a major effect on the fillet yield, which was significantly higher (38.8 vs. 33.4–34.6%) in fish belonging to the medium-size class. The lipid contents of both whole and skinned fillets were higher than those reported in the literature, ranging from 7.8 to 10.6% in whole fillets and from 5.9 to 7.6% in skinned fillets, thereby allowing classification of sunshine bass fed high-energy diets as a medium-fat fish. A significant effect of fish size on lipid content was found only for whole fillets, therefore indicating that dietary energy excess in larger fish is mainly stored as subdermal fat. The dietary fatty acid profile was found to be the major determinant of edible muscle lipid composition in all size-classes considered. The cholesterol content of muscle tissue ranged from 23 to 29 mg/100 g tissue.     

Effect of group size on feed intake, growth and feed efficiency of juvenile perch

Feed intake, growth and feed efficiency of juvenile perch Perca fluviatilis were significantly affected by group size, with fish in groups of 12 having lower feed intake, higher growth and higher feed efficiency than solitary individuals. The same trend was seen for fish in groups of 12 compared to fish in groups of four, and for fish in groups of four compared to solitary individuals, although the differences were not always significant. The high growth and low feed efficiency for fish in groups may be caused by benefits obtained from shoaling such as reduced levels of stress.     

Context-dependent group size choice in fish

The costs and benefits of group membership vary with the size of groups, and individuals are expected to modify their choice of groups in response to ecological factors such as food availability and predation risk. We experimentally examined context-dependent group size choice in a shoaling fish, the banded killifish, Fundulus diaphanus, by using nondirectional odour cues to simulate a food source or a successful attack by a predator (food or alarm treatments) in the laboratory. Group sizes were significantly smaller in the food treatment and larger in the alarm treatment than in control trials. When presented with food and alarm cues together, fish formed groups that were larger than control groups but smaller than those seen with alarm cues alone. These results are consistent with theoretical predictions based on the known benefits and costs of grouping and with previous laboratory work examining the individual shoal choice behaviour of single fish. To examine possible mechanisms of group formation, we developed an individual-based model of shoaling behaviour in which simulated fish were allowed to modify the area over which they interacted with neighbouring individuals. Group size distributions produced by the model were a good approximation of our experimental data. We suggest that local behavioural interaction rules of this type are a potential mechanism by which fish may individually adjust grouping behaviour without requiring extensive information on the position and movement of all possible shoalmates.     

Growth, pigmentation and activity of juvenile Japanese eels in relation to temperature and fish size

The growth and activity of juvenile Japanese eels Anguilla japonica in different pigmentation stages from the glass eel to the elver stage were studied in the laboratory at 15, 20 and 25° C. The growth and activity of the eels were significantly influenced by both temperature and fish size. Growth rate generally declined with increasing fish size, and fish were least active and experienced a low growth during the pigmenting stage at all temperatures. They were nocturnal and spent significantly more time moving (swimming, feeding and moving over the substratum) at 20 and 25° C than at 15° C at night within each pigmentation stage. Accordingly, they grew significantly faster at 20 and 25° C than at 15° C throughout the study. The development of pigmentation appeared to be dependant on water temperature but not on fish size. This study suggested that the growth and activity of juvenile Japanese eels were positively correlated, because fish were least active and grew slowest at low temperature (15° C) or during the pigmenting stage at all temperatures.     

Direct and size-mediated effects of temperature and ration-dependent growth rates on energy reserves in juvenile anadromous alewives (Alosa pseudoharengus)

Growth rate and energy reserves are important determinants of fitness and are governed by endogenous and exogenous factors. Thus, examining the influence of individual and multiple stressors on growth and energy reserves can help estimate population health under current and future conditions. In young anadromous fishes, freshwater habitat quality determines physiological state and fitness of juveniles emigrating to marine habitats. In this study, the authors tested how temperature and food availability affect survival, growth and energy reserves in juvenile anadromous alewives (Alosa pseudoharengus), a forage fish distributed along the eastern North American continent. Field-collected juvenile anadromous A. pseudoharengus were exposed for 21 days to one of two temperatures (21°C and 25°C) and one of two levels of food rations (1% or 2% tank biomass daily) and compared for differences in final size, fat mass-at-length, lean mass-at-length and energy density. Increased temperature and reduced ration both led to lower growth rates, and the effect of reduced ration was greater at higher temperature. Fat mass-at-length decreased with dry mass, and energy density increased with total length, suggesting size-based endogenous influences on energy reserves. Lower ration also directly decreased fat mass-at-length, lean mass-at-length and energy density. Given the fitness implications of size and energy reserves, temperature and food availability should be considered important indicators of nursery habitat quality and incorporated in A. pseudoharengus life-history models to improve forecasting of population health under climate change.     

Influence of feed ration size on somatic and muscle growth in landlocked dwarf and farmed Atlantic salmon Salmo salar

We examined the possible adaptation of the dwarf Bleke population of Atlantic salmon Salmo salar from Lake Byglandsfjord in southern Norway to limited food resources. The growth performance and muscle development in juvenile Bleke and farmed S. salar under satiated or restricted (50%) feeding were examined for 10 months, starting 3 weeks after first-feeding stage. Four-thousand fish were divided into four replicated groups and random samples of 16–40 fish per group were measured six times during the experiment. The two strains showed no significant difference in mean body mass when fed restricted ration, but the individual variation was considerably higher in the farmed fish. Both Bleke and farmed S. salar grew significantly faster when fed to satiation, but the farmed S. salar showed much higher gain in mass and were three times heavier (201.5 g vs 66.7 g) and possessed twice as many fast muscle fibres (179,682 vs 84,779) compared with landlocked S. salar after 10 months. Farmed fish fed full ration displayed both hypertrophic and hyperplasic muscle growth, while the increased growth in Bleke S. salar was entirely associated with a larger fibre diameter. The landlocked Bleke strain has apparently adapted to low food availability by minimising the metabolic costs of maintenance and growth through reduced dominance hierarchies and by an increase in average muscle fibre diameter relative to the ancestral condition.