CORRELATES OF GROWTH IN FARMED JUVENILE SOUTHERN BLUEFIN TUNA THUNNUS-MACCOYII (CASTELNAU)

In developing the mariculture of the southern bluefin tuna, there is a need to reduce handling of large tuna and to be able to assess their recent growth in research and commercial situations. The potential of various indices as correlates of growth and nutritional status was exa mined in PIT tagged juvenile tuna grown for 133 days. The study focuse d on the correlations between specific growth rate for wet weight (SGR ) or fork length (SGR(L)) and morphological (condition factor and tiss ue-somatic indices), physical (muscle temperature) and biochemical (ti ssue protein, RNA and DNA concentrations) indices. Tuna held in cages were fed twice per day to satiation on one of four feeds (defrosted pi lchards, research and two commercial prototypes), Final wet weight, ch ange in wet weight, SGR, SGR,, condition factor and white muscle conce ntrations of protein, RNA and DNA were all higher for tagged tuna fed pilchards. Irrespective of diet, the white muscle protein, RNA and DNA concentrations and the ratios between them were all significantly and positively related to SGR. Liver protein, RNA and DNA concentration a nd the protein:DNA ratio were significantly and positively related to SGR. SGR was predicted by condition factor and by muscle temperature a nd this was reflected by the positive and significant correlations bet ween muscle temperature and biochemical indices from muscle tissue. Re gression models best predicted SGR from condition, pyloric caecal soma tic index and white muscle RNA concentration and were tested by predic ting (known) SGR of tuna grown in the previous year. (C) 1998 Elsevier Science B.V.