Probiotics for freshwater fish farming can be administered as single or multiple mixtures. The expected benefits of probiotics include disease prophylaxis, improved growth, and feed conversion parameters, such as the feed conversion rate (FCR) and specific growth rate (SGR). In the current work, we review the impact of probiotics on freshwater finfish aquaculture. Data were gathered from articles published during the last decade that examined the effects of probiotics on fish growth, FCR, and water quality in freshwater fishponds/tanks. While the expected benefits of probiotics are significant, the reviewed data indicate a range in the level of effects, with an average reduction in ammonia of 50.7%, SGR increase of 17.1%, and FCR decrease of 10.7%. Despite the variability in the reported benefits, probiotics appear to offer a practical solution for sustainable freshwater aquaculture. Disease prophylaxis with probiotics can reduce the need for antibiotics and maintain gut health and feed conversion. Considering that fish feed and waste are two significant parameters of the aquaculture ecological footprint, it can be argued that probiotics can contribute to reducing the environmental impact of aquaculture. In this direction, it would be beneficial if more researchers incorporated water quality parameters in future aquaculture research and protocols to minimize aquaculture’s environmental impact.

Valorisation of crab by-products by enzymatic hydrolysis (EH) is proving to be a promising strategy to promote sustainable aquaculture and support a circular economy for crustaceans. Crab processing generates significant amounts of by-products that, if not properly managed, pose an environmental and economic challenge. These by-products are rich in chitin, proteins, and bioactive compounds and offer significant untapped potential for the development of functional feed. This review focuses on the application of enzymatically hydrolysed crab by-products as functional feed additives in aquaculture and their effects on fish growth, health management, and, consequently, human health. Recent studies have shown that EH effectively recovers chitin and bioactive peptides and improves the digestibility and bioavailability of nutrients in aquaculture. The inclusion of crude chitin, along with residual proteins and calcium carbonate, in the diet of farmed fish has been associated with increased growth, improved immune responses, and greater disease resistance, emphasising their critical role in fish health management. In addition, these functional additives contribute to the development of innovative aquafeeds with high added value and improved nutritional quality, while reducing environmental waste. Overall, the utilisation of crustacean by-products through enzymatic hydrolysis represents a valuable tool for the sustainable development of crustacean aquaculture, promotes the circular economy, and supports the development of innovative functional feeds while improving the growth and health of farmed fish, which has a positive impact on human health through their consumption.