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This study was conducted to evaluate the effects of enzymes produced by five Bacillus probiotics on growth and nutritional parameters of rainbow trout (Oncorhynchus mykiss) larvae with an initial body weight of 0.53 ± 0.19 g during 60 days. The enzyme suspension produced by Bacillus probitics resulted from culturing the bacilli in broth media with three concentrations of 1×10⁶, 1×10⁷ and 1×10⁸ CFU/100g were inoculated into the diet of rainbow trout larvae. The results of larval biometry at the end of the period of the experiment showed the following: First, the use of enzyme suspension, produced by the highest concentration of Bacillus (1×10⁸ CFU/100g) fed in T3 treatments (20.02 ± 3.77 g), caused a significant increase in the weight growth (P<0.05). Second, the same results were observed in other growth parameters, such as specific growth rate and average daily growth. Third, the use of enzyme suspension caused a significant reduction in food conversion ratio in all experimental treatments (P<0.05). The result of nutritional parameters showed the improvement of protein, lipid, energy and fiber efficiency in experimental treatment compared with the control (P<0.05). Also, the retained protein and lipid were increased significantly in experimental treatments (P<0.05). Finally, the use of enzyme suspension in this study caused improved growth performance and feed utilization in rainbow trout larvae and also increased survival rate.

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Five hundred and ninety two Siberian sturgeon (A. baerii) fingerlings (average weight, 11.1±0.9 g) were randomly distributed in 16 tanks (150 L) at a density of 35 fish per tank and fed different treatments (Control, degrading bacteria, 2% PHB, degrading bacteria + 2%PHB) for 60 days. At the end of the experiment, the results indicated that the fish fed PHB or bacteria treatments had low midgut pH and the lowest pH was observed in PHB treatment. Also PHB significantly decreased hindgut pH then the others and the lowest hindgut pH was seen in PHB treatment (p<0.05). Dietary treatments affected on the lipid metabolism in fish muscle and liver and no significant difference was observed in case of saturated, monoenoeic and total omega 6 fatty acids in fish muscle whereas the fish fed PHB with bacteria showed low linolenic acid, EPA, DHA and total omega 3 then the others.  The results in this experiment show that PHB have beneficial effects on digestive tract pH while do not change muscle omega 3 fatty acids and can be candidate as new product in aquaculture.

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This study was conducted to compare some digestive enzymes activity in juvenile Sobeity Seabream (S. hasta) under the effects of different dietary protein and lipid levels. 6 dietaries including 3 levels of protein(35, 40 and 45%) and 2 levels of lipid (7 and 14%) were determine in treatments 1 to 6. The fish with mean initial weight of 36.55±0.28 g were randomly stocked in triplicates (10 fish/tank) in eighteen 300 l tanks filled with filtered sea water at 27 ppt. The experimental fish were fed to apparent satiation thrice daily for 56 days. After the treatment period, digestive enzyme activity including total protease, alkaline phosphatase and alphaamylase was calculated. Results reveled that activity of alkaline phosphatase and totalprotease were significantly affected bydietary protein levels whereas alphaamylase activity was not affected significantly by dietary protein. No significant differences in the activity of the alkaline phosphatase and alphaamylase activity were observed at different lipid levels whereas total protease showed a significant increase at 14% lipid. A direct relationship was observed between the increase in alkaline phosphatase activity and the little decreasing trend in alphaamylase enzyme activity on the one hand and the increase in dietary lipid levels on the other hand. The interactionof dietary protein and dietary lipid significantly affected total protease activity. Results showed that efficient use of protein, digestive enzyme activity development, growth improvement and food production cost effectiveness are possible through making a balance between 40% of protein and 14% of lipid in dietary of S. hasta. In addition, determining the ratio of alphaamylaseenzyme activity to proteasecan show fish adaptability to nutrition conditions

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In a feeding trial, the effects of four levels of lipid (10, 15, 20 and 25%) and raw energy (including 18.8, 19.9, 21.4 and 22.5 kJ) with the same protein (45%) were evaluated to determine the appropriate level of lipid and dietary energy on growth performance and carcass composition of Siberian sturgeon (A. bearii). A total of 120 fish (15.6 ± 0.33 g) were randomly assigned to 12 fiberglass tanks of 500 liter (n=10 per tank)  and fed manually 3 times per day  for 12 weeks with ad libitum feeding. Results of growth trend at the end of the period showed that the fish fed with lipid content of 10 to 15 percent obtained significantly more weight gain (WG) and specific growth rate (SGR) than the fish fed with diet containing 20 and 25 percent of lipid. However the feed conversion ratio of fish fed with lipid content of 10 to 15 percent was significantly lower than other treatments. Analysis of fish carcasses indicated the significant differences in the composition of lipid, protein and ash. According to the results of present study, increasing of the lipid levels in diet of Siberian sturgeon (A. bearii) up to 15% can cause an improvement in growth rate, diet efficiency and carcass composition.

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Abstract
This study was conducted to investigate the effect of different levels of phospholipids on fatty acid profile, lipid content of body and lipase activity in stellate fish (Acipenser stellatus) fed different levels of lecithin as phospholipid source. The fish with average weight of 11.25 ± 0.06 g were fed seven different diets having identical levels of protein and lipid content but different levels of soy bean lecithin (1, 2, 4, 6, 8 and 10 percent) for 11 weeks. The fish were fed at satiety during experimental period. The results showed that using up to 10% soy bean lecithin in the fish diet increased linoleic, saturated fatty acids (SFA) and n-6 highly unsaturated fatty acids (n-6 HUFA) significantly in the fish body (p<0.05), whereas there was no significant difference in EPA and DHA levels. The results revealed that the body fat composition is significantly influenced with the fat content in the diet, however, maximum lipid was observed in fish fed 6% lecithin. The lipase activity in the digestive system of stellate fish increased significantly in the groups fed 2-4% lecithin. Therefore, we can conclude that increase in soy bean lecithin level of diet up to 4 and 6% can significantly increase the lipase activity and SFA, al MUFA and n-6 HUFA fatty acids level in the stellate fish at this weight range respectively.