Biological performance of Totoaba macdonaldi in response to dietary protein level

Totoaba macdonaldi is a carnivorous endemic fish from the Gulf of California currently being evaluated as an aquaculture candidate. Due to the lack of specific formulations for totoaba, it is usually fed with diets for other species that may or may not satisfy its protein requirement, affecting in turn its growth performance and the profitability of its culture. The aim of this study was to evaluate three dietary protein levels for totoaba juveniles cultured in a Recirculation Aquaculture System (RAS) as an early step to determine its optimal requirement at this particular life stage. A simple experimental design was used to formulate three iso-lipidic (8% crude fat) diets with 47, 52 and 55% crude protein (CP). A commercial diet (38% CP) served as a reference, but data were not included in the statistical analysis. A total of 120 juvenile totoabas were randomly distributed in 24 (250L) tanks (5 fish in every one), and each diet was assigned to six replicates. Diets were fed for 8weeks and at the end of the trial no statistical differences among treatments were observed for growth, survival, weight gain, specific growth rate, protein efficiency ratio, feed conversion ratio, survival, hepatosomatic index, or condition factor. All indices of biological performance showed acceptable values, especially when compared to other marine fish, for instance, 2.1-2.3gday^-1 of daily weight increment, 1.7-1.8% day^-1 of specific growth rate, and feed conversion ratios ranging from 2.2-2.3. Experimental diets' basic and acidic degree of hydrolysis was evaluated in vitro. The 52% CP diet showed a significantly lower (P=0.003) degree of acidic hydrolysis (92.6%). It was concluded that aquafeeds for totoaba juveniles may be formulated to contain 47% CP, but future research should evaluate lower levels of inclusion.