Discussion RESULT AND DISCUSSION

22 Figure 7. Amino-acid profile in each feed compared with channel catfish requirement g kg -1 protein.

4.2 Discussion

From the present experiment, the result showed that with the same protein supply, feed with higher fish meal content gave higher SGR than the lower fish meal one. SGR increased with protein supply for both diets. HFM diet gave the highest estimate for maximum SGR 2.57 day -1 which is reached when protein supply 23 g kg -1 day -1 and higher, while SGR still increase until 1.68 day -1 when protein supply reach 17.8 g kg -1 day -1 with LFM diet. The observed lower SGR values for both diets might be caused by too low protein supply, which can not cover protein synthesis for body mass allowing supporting optimum growth. Protein ingested by fish may presumably be catabolised to meet its requirement for maintenance rather than deposited for growth, when protein supply were too low. Protein supplies required for maximum growth in the present study values are much lower than protein supply of 23.8 g kg -1 day -1 previously recommended for patin juveniles of the same size Moreau et al. 2008. This may be related to the lower growth rate observed in the present study. Effectively, as fish may not display higher growth, protein deposition is lower and thus apparent protein requirement lower. Anyway, stricto senso protein requirement even for the same species may not be discarded from attended or target growth. 20 40 60 80 100 Lys Arg His Ile Leu Met+Cys Phe+Tyr Thr Trp Val Requirement HFM LFM 23 Figure 8. Broken line model adjusted to specific growth rate SGR of patin juveniles according to daily protein supply with the two experimental diets over 33 days. Italic values indicated minimum protein supply for maximal growth with each diet. FCR were generally improved with increasing protein supply, but HFM diet gave a better result than LFM when protein supplies are equivalent. Best FCR 0.90 are observed for HFM diet with 8 g kg -1 day -1 . At this protein supply, feed consumption was restricted, nutrient input is better utilized by fish body even growth is limited. Differences in protein supply are associated to differences in feed intake which may act on feed efficiency. Higher result of FCR such as for most dietary LFM treatment indicated that utilization of this diet was less efficient. Furthermore, high FCR with higher protein supplies indicated that these protein supplies largely exceeded the optimal need of patin, and then food will be unavoidably wasted. Body analysis indicated that dry matter, protein, ash, and GE gave the same results whatever the treatment. Fat increased with increasing protein supply on both diet. Carcass lipid levels were higher in fish fed dietary LFM. Highest fat composition 78 was achieved with LFM diet with 26 g kg -1 day -1 , while the lowest 42 and 46 were obtained with HFM diet with 8 and 14 g kg -1 day -1 protein supply, respectively. LFM diet with 26 g kg -1 day -1 protein supply, a higher feed intake, led to highest value on fat composition indicating that lipid deposition was stimulated by high nutrient supply.

17.8 16.1