# Fishman Replacement with Animal Protein Source
## 4 Discussion  
Fish are generally known to change their nutritional requirements depending on their life stage [18] and formulating feeds for different size groups to meet their dietary needs is essential. Studies conducted on fishmeal replacement by animal protein sources, as reviewed by [13], did not consider different size groups of fish when testing various ingredients in the diets. Furthermore, the control diets used in the reviewed studies were not commercial feeds and the diet formulations were used without the protein source tested [39; 40; 41; 42]. Producing high quality fish, reducing the cost of feed, and minimizing the use of forage fish in fishmeal production (pressure in the marine ecosystem) are the main reasons for the need to replace fishmeal in animal feeds [43; 44]. To our knowledge, studies conducted on the evaluation of crocodile meal as a fishmeal replacement in aquaculture for different size groups of \(O\). _mosambicus_ diets are scanty. From our previous study on the nutritional value of the Nile crocodile meal, we recorded values comparable to other by-products from poultry, such as feather meal, blood meal, and bone meal used in aquaculture diets [20]. The weight gain for fry was not significantly different among all diets. This may be because all the diets had similar crude protein level, moisture, and ash. However, fingerlings fed D6 had significantly lower weight gain than those fed D4 and D5. Sub adult to adult fish fed D4 had weight gain similar to those fed D5; the fish fed D6 had significantly lower weight gain than those fed D4 but similar to those fed D5. Diets with high-fat contents are known to have high concentrations of saturated fats and are characterized by high 18:2 n-6 polyunsaturated fatty acids (PUFA), which reduces the palatability of fish diets [17; 45]. Our results are not in agreement with the findings of [46], who reported reduced growth performance, due to the high fat content in silver sea bream _Rhabdasargus sarba_ fed a poultry by-product meal diet above the 25% substitution level. The D6 group had lower crude fat content and lower weight gain compared to those fed D4 and D5. According to [47], fish growth rate decreases as they grow older. Our study results agree with [47]'s statement, as the SGRs of \(O\). _mosambicus_ fry ranged from 7.54% to 8.11%,  
Figure 1: Feed used (grams) and cost of feed in South African rands (r) for (**a**) fry. (**b**) fingerlings. (**c**) sub-adult to adult fish. and it was significantly higher than 2.89% to 3.33% for fingerlings and 0.94% to 1.17% for the sub-adults and adults. Similar results were reported by [48] for _O. ninoticus_ fry and young tilapia. The feed conversion ratio determined by other authors is similar to GFCR in the current study, and it is defined as the amount of feed consumed to produce one unit of animal biomass gain [49]. Higher efficiency is indicated by lower GFCR values [50]. Gross feed conversion ratios of 2.16 to 2.28 in fry, fingerlings, sub-adult, and adult were observed, except for D5 (3.18) and D6 (5.24) for fingerlings, and sub adult to adult fish. Regardless of fish species, initial weight, duration of the experiment, and feeding frequency used, our results are similar to those reported for the recommended levels of other animal protein sources, such as propane worms (_Impkasia belina_), grasshopper (_Zonocerus variegate_), field cricket (_Gryllus bimaculatus_), blowfly maggot (_Chrysomya megacphala_), super worm (_Zonobas morio_), fermented feather meal, feather meal, poultry by-products, fish silage, and shrimp head meal [40; 51; 52; 53; 54; 55; 56] used in aquaculture. Our GFCR values were also within the range of 1.0 to 2.4 reported for farmed fish species, such as Atlantic salmon (_Salmo salar_), Chanel catfish (_Ictalurus punctatus_), common carp (_Cyprinus carpio_), grass carp (_Ctenopharynx-godon idella_), rainbow trout (_Oncorhynchus mykiss_), and shrimp species, such as giant tiger prawn (_Penaeus monodon_) and whiteleg shrimp (_Litopenaeus vannanei_) [49].