Culturing freshwater crayfish (Cherax quadricarinatus) in a static biofloc culture system based on fruit-wastes: Effects on growth, nutrient composition and bioeconomics

The addition of external carbon sources is central to regulating the carbon to nitrogen (C/N) ratio in biofloc technology (BFT), thereby managing microbial growth and supporting sustainable production. BFT assists with water management and cuts down operational costs by promoting microbial assimilation of nitrogenous wastes. However, dependence on⁠ conventional commercial carbon sources, such as starch and simple sugars, limits the broader adoption of BFT. The research investigates the use of locally⁠ available fruit wastes‌ as an alternate carbon source in biofloc for culturing red claw crayfish ( Cherax quadricarinatus ) under zero-water exchange culture conditions. Five treatments, including three fruit waste sources, namely, banana peel (BP), orange peel⁠ (OP) and pineapple peel (PP), were tested in quadruplicate‌: ‌against molasses (M‌O) and⁠ a no-biofloc (NB), as a control. Each system was maintained at a fixed C: N ratio of 15: ⁠1. The proximate composition, including the mineral composition of the fruit wastes, was determined before the commencement of the cultural experiment. Water quality parameters, biofloc development, crayfish growth, size-distribution of crayfish and bio-economic analysis were assessed at the end of the experiment. The results showed that the OP had the highest protein and carbohydrate contents, as well as the highest carbon and nitrogen percentages (p < 0.05). The results at the end of the experiment showed that the fruit waste-based BFT yielded optimal water quality. Growth performance, including weight gain, specific growth rate and final carapace length and width, was significantly higher in PP and BP treatments, which also exhibited higher protein efficiency ratios. Potassium (K) was highest in molasses and banana peel, magnesium (Mg) was highest in BP only, whereas ⁠sodium (Na) was highest in PP and MO BFT. Economic analysis revealed that the MO had the highest production cost, whereas PP and BP were the most ⁠cost-effective. These findings highlight the potential of fruit waste, ⁠particularly PP, as a low-cost, eco-friendly carbon source for BFT in indoor culture of red claw.