Nutritional evaluation of insect meals as substitutes for fishmeal in oreochromis mossambicus and clarias gariepinus diets

Abstract

The aim of this thesis was to investigate the potential of enhancing freshwater fish production through replacement of fishmeal with insect meals. The effect of dietary full-fat Stinkbug (Encosternum delegorguei) meal on growth performance, blood serum chemistry, liver and intestinal histology, and digestive enzyme profile of Oreochromis mossambicus and Clarias gariepinus was evaluated. The Stinkbugs were purchased from the Thohoyandou Town open market. Five diets were formulated to partially substitute fishmeal at 0, 10, 30, 50, and 70%. The diets were formulated to be isonitrogenous (30% crude protein), isolipidic (12% fat content), and isocaloric (15 MJ/Kg). Oreochromis mossambicus juveniles (4.2 ± 0.3 g) were stocked randomly in triplicates at 15 fish per tank. Clarias gariepinus fingerlings (6.4 ± 1.02 g) were stocked randomly in triplicates at 5 fish per tank. The experimental system used for both species was the same. There was a decline in growth performance indices (SGR, TGC, FI, PER, APDC) with an increase in Stinkbug meal inclusion in both O. mossambicus and C. gariepinus. The decline in growth performance was more evident in inclusion levels above 30% in both species and it was attributed to the poor amino acid profile of the Stinkbug meal and its low (29%) protein content. The organosomatic indices (CF, VSI, HSI) were not influenced (P>0.05) by the inclusion of Stinkbug meal. The AST and ALT levels significantly increased at the highest inclusion level (P<0.05) in both O. mossambicus and C. gariepinus. This shows that an inclusion level above 50% may pose stress to these fish species. However, the liver and intestinal histology showed no significant alterations with higher inclusion levels in both O. mossambicus and C. gariepinus. This showed that the inclusion of the Stinkbug meal in the diets of these two species did not affect their liver and gastrointestinal tract. The digestive enzyme profile (amylase, protease, and lipase) showed that both O. mossambicus and C. gariepinus are probably equipped to utilise insect-based diets. Despite the decline in growth performance, cost-benefit analysis showed that the Stinkbug meal may be a sustainable alternative to fishmeal. Due to poor amino acid, fatty acid profiles, and the low inclusion level of the Stinkbug meal, it was thus prudent to search for locally available alternative insects to potentially replace fishmeal in the diets of O. mossambicus and C. gariepinus. The Alates termites have a better nutritional profile than the Stinkbug meal and are widely available. The utilisation of the Alates termite meal (M. falciger) based diets was compared between O. mossambicus and C. gariepinus. De-winged Alates termites were purchased from the Thohoyandou Town open market. Diet formulation and experimental set-up were adopted as in the previous chapter. The Alates termite meal replaced fishmeal up to 50% without compromising the growth performance of O. mossambicus and C. gariepinus. The higher inclusion level (50%) in Alates termite meal was partly attributed to its protein content (40.46%) which meets the requirements for O. mossambicus (30%) and C. gariepinus (40%). Moreover, the Alates termite meal recorded an Essential amino acid index (EAAI) (1.87) which was higher than the Stinkbug meal EAAI (0.11). However, at inclusion levels above 50%, SGR, WG, TGC, FI, PER, and APDC significantly declined (P<0.05) in both species. The organosomatic indices followed a similar trend. The ALT and AST levels were not influenced by the inclusion of Alates termite meal in O. mossambicus. On the other hand, these enzymes were significantly (P<0.05) elevated at inclusion levels above 50% in C. gariepinus. This shows that inclusion levels above 50% may impose stress on C. gariepinus. The liver and intestine of both fish species were not compromised even at the highest inclusion level. Normal histological micrographs of the liver and intestine were observed across experimental diets in both species. The cost-benefit analysis showed that substituting fishmeal with the Alates termite meal is economically viable. Defatting the Alates termite meal is recommended before incorporation into fish diets. The major limitation of Alates termites is their seasonal variation. It was thus important to search for an insect that could be harvested throughout the year within the geographical area. The Soldier termite caste of M. falciger was also used as a potential insect to partially replace fishmeal in the diets of O. mossambicus and C. gariepinus. Unlike the Stinkbugs and the Alates termite, the Soldier termite is one of the insects that is available throughout the year. The Soldier termites were purchased from the Thohoyandou Town open Market. The same experimental diet formulation procedure was adopted as in the previous chapters. Juvenile O. mossambicus (9.70 ± 1.2 g) were randomly stocked in triplicates at a stocking density of 10 fish per tank. On the other hand, C. gariepinus fingerlings (5.3 ± 0.8 g) were randomly assigned their diets in triplicates at a stocking density of 5 fish per tank. The best growth perfomance parameters (SGR, TGC, FI, PER, APDC) were recorded at the 50% inclusion level in O. mossambicus. On the contrary, a decline in growth performance with an increase in the Soldier termite meal was observed in C. gariepinus. Inclusion levels beyond 10% significantly reduced the growth performance and nutrient utilisation of C. gariepinus. The difference in growth performance of these two species was ascribed to their feeding habits. Herbivorous fish species have shown the potential to utilise diets with higher insect meal inclusion levels. The organosomatic indices were not (P>0.05) influenced by the inclusion of Solider termite meal in the diets of both O. mossambicus and C. gariepinus. The study showed that the health status of both fish species was not compromised. Histomorphology micrographs also confirmed the normal health status observed in both fish species. The study further showed that O. mossambicus and C. gariepinus have different digestive enzyme profiles and are differently equipped to digest insect-based diets. Substitution of fishmeal with Soldier termite meal may yield higher profit margins than using fishmeal-based diets in O. mossambicus and C. gariepinus. The study showed that locally available insects have the potential to replace fishmeal in the diets of two commonly cultured warm freshwater species. The Alates termite meal is recommended to replace fishmeal in the diets of both species. The Soldier termite meal is recommended to replace fishmeal in the diet of O. mossambicus. Defattening of the Stinkbug meal is also recommended before incorporating into the fish diets. Digestion can also be improved through supplementation of Natuzyme50® in fish diets. This study showed that the use of locally available insects in the diets of commonly cultured freshwater species has the potential for higher profit margins in aquaculture enterprises. However, a detailed economic analysis is recommended. This may increase warm freshwater aquaculture production and improve the livelihood of local fish farmers.