## 4 Discussion  
From the results of this review, a variety of fish species, sizes, and inclusion levels have been used in aquaculture (Table 2). A variety of fish species, sizes, and inclusion levels may be because aquaculture is an incredibly diverse industry in terms of species cultured and production systems used [1]. Different fish species have different nutrients requirements [37], which affect the level of protein source inclusion in tested diets. According to [38], human health benefits, competitive price, fish safety, efficiency, customer acceptance, minimal contamination, and ecosystem stress are factors in selecting feeds. Growth performance measured by final weight and specific growth rate showed that excess protein could not be used efficiently for growth because of growth energy used for the deamination and excretion of absorbed excess amino acids. After all, each fish species had a specific protein limit [39]. According to [40; 41; 42; 43], when dietary protein levels increase, the feed conversion ratio decreases. Results from this review indicated that  
Figure 5: The effect size of survival rate (%) of fish from different studies fed different animal protein sources compared to fishmeal as a protein source. O. mossambicus_ and _C. gariepinus_ fed insect meal (_I. belina_, _Z. variegatus_ and _G. bimaculatus_), respectively, converted their feeds efficiently. Both freshwater and marine fish species utilize insects as part of their natural diet [44]. Insects are rich in amino acids, lipids, vitamins, and minerals [45], and they do not require arable land, water, or energy to reproduce [46]. Besides, insects are more natural to replicate, have a higher growth rate, and very effectively transform low-grade or organic matter into high-value protein quite efficiently [44,47]. Recommended levels reported for insect meal in this review shows that a total fish-meal replacement has not been successful. Results support findings reported by [44], who suggested dietary unbalance or deficiencies as the main reason. According to [48], limitations of using insects include their (i) varying nutritional value, which is dependent on the species, stage of development, and the substrate used to feed the insect, (ii) low concentration of sulfur-containing amino acids, and (iii) absence of eicosapentaenoic and docosahexaenoic. Orecchromis niloticus, C. gariepinus, L. gattatus, O. niloticus, and Op. argus also efficiently converted terrestrial by-products (fermented feather meal, feather meal, poultry by-products, poultry by-products, and meat and bone meal). Like other animal protein sources, fishery by-products (fish silage, shrimp head meal, and krill meal), fed to Red tilapia (_O. mossambicus_\(\times\)_O. niloticus_\(\times\)_O. aureus_), _C. gariepinus_ and _A. glabelenstaedtii_, respectively resulted in acceptable feed conversion ratios of 1.35, 2.50, and 1.10, respectively. Survival rates ranged from 83% to 100%, except for Red tilapia (_O. mossambicus_\(\times\)_O. niloticus_\(\times\)_O. aureus_) and _C. gariepinus_, which was not reported. Fermented feather meal, blood meal, poultry by-products, feather meal, meat and bone meal are some of the terrestrial animal by-products used in aquaculture diets [15; 16; 17; 18; 19]. Terrestrial by-products have been reported to have great potential as fishseal replacement because they are readily available, economical sources of protein and have more complete amino acid profiles than vegetable proteins [23]. The use of feather meal in aquaculture feeds is limited by the fact that fish are unable to digest it. Lysine, methionine, and isoleucine have been reported as limiting essential amino acids in poultry by-products, meat and bone meal, and blood meal, respectively [22]. Consumer acceptance is the primary constraint on the use of rendered animal products [23]. Fishery by-products are products generated from fishery industries [41].