Assessment of dietary taurine essentiality on the physiological state of juvenile Totoaba macdonaldi

Information on specific nutrients like taurine is important to support a nutritionally balanced diet for marine species such as totoaba Totoaba macdonaldi under culture conditions. Eight isoproteic (50%) and isolipidic (12%) experimental diets were formulated to contain graded levels of taurine (0.23%, 0.45%, 0.91%, 1.28%, 1.76%, 2.20%, 2.72%, 3.01% as-is) using ethanol-washed fishmeal (FM) as primary protein source. Green liver, low gallbladder-somatic index (GBSI), low apparent digestibility coefficient (ADC) of lipid, low erythrocyte turnover, low plasma cholesterol and triglycerides, as well as low visceral fat, were detected in the basal diet (T-0.23) after 10 weeks. Thermal-unit growth coefficient (TGC) was best modelled by a five-parameter saturation kinetic model (5-SKM, p < .001) with marginal differences (R2 = .13) of juvenile totoaba (initial weight 10.0 ± 1.0 g). Low GBSI (0.095%) was accompanied with low ADC of lipid (78.9%) in the low-taurine diet (T-0.23). GBSI and ADC of lipid were best modelled by four-parameter SKM (4-SKM, R2=.72 and .87, respectively, p < .001). Plasma cholesterol increased linearly with dietary taurine (R2 = .75, p < .001), while plasma triglycerides increased quadratically (R2 = .53, p < .001), suggesting modulations of lipid metabolism in totoaba. Plasma bilirubin levels increased linearly, and the lowest concentration was found in the basal diet (T-0.23); however, haematocrit and haemoglobin levels were changed slightly between the treatments. This study demonstrates that supplementation with a low level of taurine (0.45% as-is) in a washed FM-based diet can normalize the physiological condition of juvenile totoaba. Green liver, GBSI, ADC of lipid, plasma cholesterol and triglycerides may be informative diagnostic tools for taurine deficiency in totoaba.