Dietary protein requirement of lemon fin barb hybrid (Barbonymus gonionotus Bleeker 1849 ♀ × Hypsibarbus wetmorei Smith 1931 ♂) fingerlings

Lemon fin barb hybrid (female Barbonymus gonionotus × male Hypsibarbus wetmorei) was first produced in 2004 with a novel intention as a poor man’s fish. At present, the fish is commercially raised with tilapia or catfish diets since no specific diet has been developed for the hybrid. As protein is the most important and costliest component in an aquafeed, the dietary protein requirements of lemon fin barb hybrid fingerlings were investigated in this study which included the optimal dietary protein and energy requirements, the effectiveness of defatted black soldier fly (Hermetia illucens) meal, poultry offal meal and soybean meal as fishmeal replacement and the apparent digestibility coefficients (ADC) of selected feedstuffs. Practical test diets were used in all feeding trials and the effects of these diets on the growth performance, proximate body composition, nutrient and amino acid retentions, and histopathological parameters of the fish were determined. In Experiment 1, five isocaloric (16 kJ g-1) diets containing varying protein levels ranging from 20 to 40% were tested. Six diets with three dietary protein levels (25, 30 and 35%) and two energy levels (16 and 17 kJ g-1) were evaluated in Experiment 2 while the performances of five isonitrogenous (30% protein) and isocaloric (17 kJ g-1) diets with varying dietary level of defatted black soldier fly pre-pupae (BSFP) meal (0, 25, 50, 75 and 100%) as fishmeal replacement were assessed in Experiment 3. In Experiment 4 and 5, similar experimental protocols as in Experiment 3 were adopted in which poultry offal meal (POM) and soybean meal were tested as fishmeal replacement, respectively. Best diets from Experiments 3, 4 and 5 were simultaneously evaluated in Experiment 6 while in Experiment 7, the apparent digestibility coefficient (ADC) of dry matter, nutrients and energy of fishmeal, defatted BSFP, defatted POM, defatted soybean meal, rice bran and corn meal, and their apparent availability coefficent (AAC) of amino acids in the hybrid fish were studied. The fish growth and body composition in Experiment 1 indicated that the optimal dietary protein requirement of lemon fin barb hybrid fingerlings was 34.6% at 16 kJ g-1 gross energy. In the subsequent experiment, the best fish performance was observed at a lower 30% protein and a higher 17 kJ g-1 gross energy with a protein-energy ratio of 16.64 mg protein kJ-1. In Experiment 3, it was found that defatted BSFP meal could replace up to 75% fishmeal without affecting fish survival, growth performance, body composition, nutrients and amino acid retentions and histopathological parameters. Similar findings were made in Experiment 4 when poultry offal meal was used as the fishmeal replacement. In Experiment 5, soybean meal was found to could only replace up to 50% fishmeal. The findings of Experiments 3-5 indicated a minimal of 2.5 and 5% fishmeal were required in the hybrid fish diet when animal and plant based protein sources were used as partial fishmeal substitute, respectively. When the best diets from Experiment 3-5 were simultaneously tested, defatted BSFP as partial fishmeal replacement gave the best growth performance followed by defatted POM and defatted soybean meal which suggested that animal proteins were superior to plant proteins for the hybrid. In the digestibility study, the results indicated the lemon fin barb hybrid had a higher digestive capability to utilize animal protein sources especially fishmeal compared to plant based meals. Corn meal was poorly digested by the hybrid fish. In conclusion, the findings of this study provided an important and vital information for the development of a practical specific diet for lemon fin barb hybrid.

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