The effect of different initial size distributions on the growth of Atlantic halibut

Abstract

Growth rate of individually tagged medium-sized (249 6·9 g) juvenile halibut was 18% lower when medium sized fish were reared alone (treatment Mm) as compared with rearing with either large/dominant (382 12·1 g) (Ml) or small/subordinate (158 3·1 g) (Ms) conspecifics. The coefficient of variation of weight of medium-sized fish increased with weight in both the Mm and the Ml group whereas it was stable in the Ms group. Size rank correlation between initial and final weight was highest in the Mm group and lowest in Ms. A negative rank correlation was found also between initial weight and overall growth rate for the Ms treatment groups but not the other groups. It is hypothesized that interactions between similar-sized individuals in the Mm treatment group had an inhibiting effect on growth as social hierarchies were being resolved. 2000 The Fisheries Society of the British Isles

Best among unequals? Effect of size grading and different social environments on the growth performance of juvenile Atlantic halibut

“…; y p À Á for each p (age) measurement on n individual fish; X(n 9 q) is the design matrix or the set of extraneous variables measured for each individual, i.e., q = age p + grading group i + replicate j ; (i = Control, LS, SS, LL and SL), (k = replicate a, replicate b); B(q 9 p) is the matrix of parameters estimated by the model; and E(n 9 p) is the matrix of deviations for each individual from the expected value of Y = XB. Two-way nested ANOVA (Searle et al 1992), where the two replicates were nested within experimental groups, was used to calculate the effect of different social environments on mean weights and specific growth rates. The model equation of the nested ANOVA had the form:…”

Efeito da densidade de estocagem na homogeneidade do crescimento de juvenis de pirarucu em ambiente confinado

“…Criações em tanques-rede de pequeno volume podem ser mais vantajosas que as criações tradicionais, uma vez que permitem altas densidades de estocagem e, quando ideais, podem quebrar o status social de dominância e subordinação (Alanärä & Brännäs, 1996), tendendo à manutenção de lotes mais homogêneos (Trzebiatowski et al, 1981;Teskeredzic et al, 1986) e, conseqüentemente, aumentando a produtividade (Hengsawat et al, 1997). A estocagem de lotes de peixes com tamanhos homogêneos iniciais influenciam na homogeneidade do lote final (Stefansson et al, 2000).…”

Effect of size grading on sea bass (Dicentrarchus labrax) juvenile self-feeding behaviour, social structure and culture performance

“…They hypothesized that fish competition was very high just after size grading, and decreased with time. In some species, size grading might lead to the destruction of size hierarchy, the growth of the large fish being adversely affected by the stronger agonistic interaction, and intraspecific aggression occur among the graded large individuals (Baardvik and Jobling 1990;Stefánsson et al 2000;Sunde et al 1998). In sea bass, no studies have reported a high level of aggression under self-feeding conditions, as the reward level after each trigger actuation usually optimizes feed allocation to the group.…”

“…Some experiments supported the usefulness of grading procedures based on asymmetric competition (abalone, Haliotis tuberculata, Mgaya and Mercer 1995), while others reported either lower growth rates in graded fish (cod, Gadus morhua (Lambert and Dutil 2001) or no biomass gain: Arctic charr, Salvelinus alpinus (Wallace and Kolbeinshavn 1988;Baardvik and Jobling 1990); Atlantic salmon, Salmo salar (Gunnes 1976); eel, Anguilla anguilla (Kamstra 1993); Dover sole, Solea solea L. (Overton et al 2010). In some species, destruction of size hierarchies does improve the growth of the small fish but the growth of the large fish could be adversely affected by the stronger agonistic interaction and intraspecific aggression occurring among the graded large individuals (Baardvik and Jobling 1990;Sunde et al 1998;Stefánsson et al 2000). Furthermore, size grading is in itself a stressful procedure for fish (Pickering 1981) and is labour-intensive, with risks of handling damage, disease outbreak, and growth reduction (Sunde et al 1998).…”

“…Variation in individual growth is a common feature in many cultured fish stocks (Huntingford et al 1990;Stefánsson et al 2000;Smith and Fuiman 2003). Magnuson (1962) defined growth depensation as the increase in the variance of size distribution over time, due to differences in growth rates.…”