Evaluation of Imbrasia belina meal as a fishmeal substitute in Oreochromis mossambicus diets: Growth performance, histological analysis and enzyme activity

- Mopane (Imbrasia belina) worm has the requisite protein, amino acids, fat and fatty acid profile to optimally sustain growth of Oreochromis mossambicus.
- O. mossambicus is physiologically adapted to handling high protein levels in mopane worm. Protease activity increased with higher mopane worm inclusion levels.
- Growth performance indices increased with higher mopane worm inclusion levels. This is contrary to most previous studies when insects were used to replace fishmeal.
- No histological alterations of the liver and intestines were evident at high mopane worm inclusion levels. This indicates that mopane worm meal did not affect the health of the fish.

The main objective of this study was to investigate mopane worm (Imbrasia belina) as a protein source in the diet of Oreochromis mossambicus. One thousand five hundred O. mossambicus fingerlings (40 ± 2.5 g) were fed five isonitrogenous, isolipidic and isoenergetic diets formulated to contain 30% crude protein and 20 MJ/kggross energy (dry matter basis) for 51 days. Fifteen indoor rectangular concrete tanks (1.5 m3) connected to a recirculating system were used. Water temperature ranged between 27 and 29 °C. The diets were prepared by replacing fishmeal with mopane worm meal at 10%, 20%, 40% and 60%. The diets were coded D2, D3, D4 and D5 respectively. A control diet with no mopane worm meal was coded D1. The diets were fed to triplicate groups of O. mossambicus twice a day. Specific growth rate (SGR), Thermal-unit growth coefficient (TGC), protein efficiency ratio (PER) and apparent digestibility coefficient (ADC) increased with higher inclusion levels of mopane worm meal. Feed conversion ratio (FCR) also improved with higher inclusion levels. However, the highest growth performance (SGR: 3.49%; FCR: 1.29) was recorded in fish fed the fishmeal based control diet. Protease, amylase and lipase activities were determined in the intestines. Both protease and amylase activity were significantly higher (P < 0.05) at high mopane worm inclusion levels. It is suggested that the high protein levels of the mopane worm diet elicited high protease activity. The health status of the fish was evaluated by examining the liver and intestine histology. There were no evident histological alterations of either liver or intestine as mopane worm meal inclusion levels increased. This showed that mopane worm meal may be a good candidate for the replacement of fishmeal in O. mossambicus diets. The highest profit index (1.67) was recorded in the 60% mopane worm inclusion level. The lowest profit index was in the control. More studies on mopane worm meal as a substitute of fishmeal are recommended in other fish species.