During the E. tarda challenge test, the first dramatic mortality was observed on the third day after injection, and the fish fed the Con and KH diets showed lower disease resistance compared to those fed the TH diet (Fig. 1). Although fish fed the TH diet exhibited numerically higher disease resistance than the two other experimental groups, the differences were not significant at the end of the challenge test.
The fish fed the KH diet showed significantly (P b 0.05) higher growth performance than those fed the Con diet. Significantly lower feed conversion ratio was obtained in fish fed the KH diet compared to those fed the Con diet. Fish survival varied from 82 to 87% without any significant differences among dietary treatments. Digestibility of dry matter and protein was significantly higher in fish fed hydrolysate containing diets (Table 3).
The results of whole-body composition analysis (Table 4) and hematological indices (Table 5) revealed no significant differences among treatments.
Dietary supplementation of the KH significantly increased NBT and SOD activities. Also, significantly higher lysozyme activitywas recorded in fish fed TH diet. Total Ig level and antiprotease activity were not significantly influenced by the dietary treatments (Table 6).
All the fish in the control group were dead within six days following the bacterial infection,while the other two groups exhibited higher disease resistance even 10 days post infection (Fig. 1). However, the differences were not significant among treatments.
Whole-body composition of red sea bream and olive flounder fed the experimental diets
for 12 and 9 weeks, respectively.
In the present study, significant improvements in growth performance of red sea bream and olive flounder were achieved by dietary supplementation of KH. Similarly, Kolkovski et al. (2000) reported the growth promoting effect of KH when it was supplemented in diets for larval and juvenile fish.
Increased growth performance of fish following dietary KH application has been reported to be due to enhanced diet ingestion rate as KH is a rich source of low molecular weight compounds
acting as chemo-attractant in fish diets (Kolkovski et al., 2000).
In the
current study, slight improvement in feed intake was observed in
groups offered KH coated diets and thiswasmore evident in olive flounder,
although the differences were not significant. Therefore, the potential
attractive properties of KH may not fully explain the considerable
improvement of fish performance in the present study.