BACKGROUND: The use of natural immune stimulants is one of the most effective methods for strengthening immunity and preventing diseases in fish. OBJECTIVES: Due to the abundance of red algae (Laurencia caspica) in the Caspian Sea, the aim of this study was to investigate the effect of this algae on growth performance and blood indices of rainbow trout. METHODS: The present study was performed on 750 randomly selected rainbow trout (Oncorhynchus mykiss) in 5 experimental treatments including an algal extract-free diet (control), and diets supplemented with 0.5, 1, 1.5, and 2% of algal hydroalcoholic extract. During the experimental period, fish were sampled to measure growth performance and blood indices every two week for 8 weeks. RESULTS: Growth indices were not affected by the algal extract at the end of eight weeks of feeding. There were no significant differences in fish survival at different treatments. Total counts of red blood cells, white blood cells, hematocrit percentage, hemoglobin concentration and neutrophil and monocyte percentages were affected by algal extract with significant increases compared to the control group (p < /em><0.05). Results of serum biochemistry showed that significantly increased total protein, albumin and globulin and also significantly reduced ALT, AST and ALP compared to the control in rainbow trout. CONCLUSIONS: Based on the results of this study oral use of red algae (L. caspica) as an immune stimulant in rainbow trout (O. mykiss) was recommended.

BACKGROUND: Balance in the amount of minerals in the aquatic animal’s diet is very important. Phosphorus is one of the most important minerals in fish and aquatic animal’s nutrition. Phosphorus is important not only for the proper growth and fish health, but also for excessive phosphorus excretion that may cause water pollution and algal bloom. OBJECTIVE: In this study the effects of adding monoammonium phosphate in the diet of fish (Cyprinus carpio Koi) and its comparison with monocalcium phosphate were investigated. METHODS: 650 koi fish weighing 17 g were distributed in 15 tanks (5 treatments - each in three replicates) and mono-ammonium phosphate-fed diets at three levels (0.75, 1.5 and 3% of the diet), monocalcium phosphate in one level (3% of the diet) and a control group (no phosphorus supplementation) were fed for 8 weeks. RESULTS: Growth indices and feed conversion ratio in fish fed 3% monoammonium phosphate showed the best results. The control group showed the lowest weight gain and the highest feed conversion ratio. Blood phosphorus was also significantly correlated with increasing monoammonium phosphate. The highest level of calcium in the blood was observed in the group fed monocalcium phosphate (3%). CONCLUSIONS: Considering the improvement of growth and nutrition indices, adding 1.5 to 3% monoammonium phosphate in the diet of koi fish was suggested.