Protein requirements for optimum growth of Liza ramada fry (Mugilidae) at different water salinities

Abstract

The effects of dietary protein level and water salinity on growth rates, feed utilization and body composition of mullet Liza ramada (synonymous of Mugil capito Cuvier, 1829) fry were investigated. Four isocaloric (18.8 kJ GE/g) diets containing 25, 30, 35 and 40% protein levels were prepared. Each diet was fed to duplicate groups of L. ramada fry (0.13 g mean weight and 24.6 mm mean length) reared at 4 different salinities (0, 12, 24 and 36‰) to satiation, twice a day for 70 days. The fish which were reared at 0 salinity exhibited poor growth and feed conversion concomitant with high mortality rates. At salinities in the range of 12–24‰, the best growth and feed conversion were achieved at 40 and 35%, dietary protein levels, respectively. At full-strength sea water (36‰), optimum fish performance was achieved at 30% dietary protein. At all salinities, protein efficiency ratio (PER) and protein production value (PPV) were negatively correlated with dietary protein level. With the exception of body ash, carcass composition Was significantly affected by dictary treatments. At all salinity levels, body water and protein were positively correlated to dietary protein, while carcass lipid showed a negative correlation. Body ash was higher in the fresh water groups than in those reared in brackish and sea water.