Evaluation of the effect of diet containing different levels of yeast (Saccharomyces cerevisiae) on growth indices, carcass biochemical composition and total bacterial count in a combination of rainbow trout and peppermint (Mentha piperita. L)

In this study with using plant proteins and yeast, several balanced protein diets were made with the aim of reducing the consumption of fish meal. Rainbow trout fingerlings (Oncorhynchus mykiss) to experimental diets and cultured in the aquaponics systems. The experimental treatments were control treatment (commercial diet), treatment 1(25% Fish meal (M)  and 57% (Plant protein) pp, treatment  (23%FM,4%yeast,47%pp) treatment3 (20%FM,9%yeast,52%pp) ,treatment4 (18/5%FM,14/5%yeast,46%pp),treatment5 (17%FM,21%yeast,41%pp), treatment6(10%FM,25%yeast,45%pp),treatment7(28/5%yeast,45%pp).The160 rainbow trout fingerlings with an average weight of 38 ± 2 and the 320 seedlings of peppermint (Mentha piperita) with an average weight of 25±2 gr were randomly introduced to the 16 experimental units and cultured for nine weeks. The results showed that the growth performance of fish such as final weight, specific growth and protein efficiency rates increased in treatment 3 compared to other treatments (P<0/05). Carcass composition showed that the highest amount of crude protein was observed in treatment 3, the highest fat crude was observed in control treatment, the highest moisture content was obtained in treatments 6 and 7. And there was no significant difference in ash content between treatments(P>0/05). The data from total bacterial count showed that the highest total count of bacteria in the intestine, reservoir water, and plant roots belonged to treatment 5, and the other treatments did not have any significantly differences. It seems that in these treatments, there were an equilibrium among bacteria of fish intestines, reservoir water, and plant roots. The best experimental diet in combination with rainbow trout and peppermint was recorded in treatment 3, and it was demonstrated that to grow rainbow trout using diets containing vegetable proteins, yeast, without using fish meal, is possible but to get the best growth conditions, it is needed to have at least 10% fish meal in the diet.