Effects of grading on individual growth and feeding behaviour of European seabassDicentrarchus labrax

Abstract

Triplicated groups of six small‐size (S, 70.3 g), six large‐size (L, 96.3 g), and six mixed‐size (S + L) fish consisting of three small [S(S + L): 67.5 g] and three large fish [L(S + L): 97.5 g] were reared for 75 days. Fish were individually marked. In all treatments, a feeding hierarchy was established; fish of the highest feeding ranks had the higher mass and specific growth rate (SGR), consumed the majority of food offered with little daily variation, and made more efforts to claim food. Correlation coefficients for S(S + L) and L fish were lower compared to S and L(S + L) fish respectively. The same was observed for the correlation coefficients between mean share of meal and coefficient of daily food consumption variation thus indicating a milder social environment for S(S + L) and L fish. S(S + L) fish had significantly higher SGR, mass gain, and condition factor than S fish. S(S + L) and L fish had a greater percentage of fish consuming the ideal amount of food and obtaining satisfactory feed efficiency than S and L(S + L) fish. Present results indicate that, within the range of body mass examined, grading is beneficial for the large fish but not for the small ones. Grading effects are strongly associated with changes in the strength of social hierarchies.

Effect of size sorting on growth, cannibalism, and survival in Eurasian perch Perca fluviatilis L. post-larvae

“…Moreover, in aquaculture industry, good practices usually aim to minimize fish size heterogeneity over the time in order to improve feeding efficiency through adequate food ration and further benefit based on minimizing growth dispersion, yielding greater stocks of marketable fish at the same time (Kestemont et al 2003;Petrović et al 2011). The positive effects of size grading on the growth of juvenile Atlantic salmon, Salmo salar (Gunnes 1976) sea bream, Sparus aurata (Popper et al 1992), Nile tilapia, Oreochromis niloticus (Brzeski and Doyle 1995), and European sea bass, Dicentrarchus labrax (Batzina et al 2018) have already been reported. In the other hand, there are reports indicating that growth rate was not improved in size-graded groups compared with non-sorted groups of several fish species (Baardvik and Jobling 1990;Sunde et al 1998;Barki et al 2000;Wallat et al 2005;Imsland et al 2009).…”

Grading frequency affect the growth performance and intra−cohort cannibalism in African catfish (Clarias gariepinus, burchell, 1822) culture

“…Moreover, size grading practices have been advocated method to control large differences in size of fish during the nursery period of many piscivorous fish species (Baras & Jobling, 2002). Sorting also optimizes feeding, since granulation and ration sizes can be tailored to the fish size (Batzina et al, 2018). The C. gariepinus is highly cannibalistic at the early larval stage (Baras, 2013) but knowledge of the changes in the species age and cannibalism is still scanty.…”