ABSTRACT
Among the wide variety of alternative ingredients aimed to substitute fish meal in aquafeeds, insect meals have been recently proposed as novel, nutritionally good dietary components. In the present study, five isoproteic and isoenergetic experimental diets formulated with varying dietary levels of Madagascar cockroach meal substituting fishmeal on a dietary protein basis (0, 25, 50, 75, and 100%) were supplied to.Nile tilapia juveniles (Oreochromis niloticus) for 29 days. Production parameters were compared among treatments, and the relative assimilation of the dietary nitrogen supplied by fishmeal and insect meal was estimated. To this end, nitrogen stable isotope analyses were applied to diets and fish muscle tissue. The isotopic changes elicited by the experimental ingredients were used to estimate the time required to reach isotopic equilibrium, the nitrogen turnover rates, and nitrogen residency times in muscle tissue. The latter were short and ranged from 4.7 to 6.2 d, except in diet containing 100% cockroach meal (7.8 d). No statistical differences were detected in final mean weight, specific growth, and survival rates among treatments. The relative proportions of dietary nitrogen and total dry matter supplied by insect and fish meal to growth were similar to the established dietary proportions after these were corrected for their respective apparent digestibility coefficients. The cockroach meal present in diets containing both main ingredients supplied relatively high proportions of dietary nitrogen (from 16 to 69%) to the biosynthesis of fish muscle tissue.
