Yellowtail kingfish farming is growing in Europe with high emphasis on recirculating aquaculture systems (RAS), while in Australia, Japan and Latin America the industry continues to expand predominantly through sea-cage farming. It is a carnivorous species that requires high dietary protein, and to date, fishmeal (FM) rich feeds are common to support its rapid growth. However, this brings the challenge of high phosphorus (P) content on these diets which could be poorly retained given
a more complex matrix bone-bound P, resulting in significant P excretion and discharge. The latter continues to be of environmental concern and stricter regulations governing P release to the environment are arising across the globe regardless of culture systems. With this in mind, this study aimed to aid on the management of P in Seriola farming by investigating the effects of fishmeal inclusion and dietary P levels on performance and effluent discharge.
Results
Growth Performance
All treatments supported strong growth, with fish increasing from an average of 65 g to approximately 350 g over the 7-week period. Importantly, no significant differences were observed in any of the performance parameters measured, including survival, specific growth rate, feed intake, or feed conversion ratio across treatments.
Fish harvest quality
In the same manner, final harvest quality parameters were not significantly affected by dietary fishmeal level or total phosphorus. Proximate composition parameters, including moisture content, total phosphorus, and protein, showed no significant differences among treatments. Additionally, no significant main effects of fishmeal or total phosphorus, nor their interaction,
were observed for hepatosomatic index (HSI), viscerosomatic index (VSI), or condition factor (K). Overall, fish fed reduced fishmeal diets (30%) performed equally well as those fed increased (47% FM), indicating that lower fishmeal levels can support growth when key nutrients are balanced appropriately.
Phosphorus Discharge
On the other hand, by reducing dietary phosphorus in low fishmeal diets decreased orthophosphorus excretion by 25% and total phosphorus discharge by 21%. P discharge values calculated as per 1000kg feed given. A similar trend was observed in high fishmeal diets, where lowering dietary phosphorus reduced orthophosphorus excretion by 36% and total phosphorus discharge by 26%.
These results confirm that mitigating environmental P emissions while sustaining performance in yellowtail kingfish farming requires an integrated approach:
optimizing total dietary P levels and employing strategic ingredient selection.
About the Author
Sandeep Sharma is a Scientist in the Nutrition and Formulation team within Global R&D at BioMar. His work focuses on fish nutrition and aquafeed development, with particular expertise in amino acid nutrition, micronutrients such as vitamins and minerals, and functional feed additives. He works across a range of marine species, including yellowtail kingfish, barramundi, seabass, seabream and flatfish, supporting the development of nutrition strategies for modern aquaculture systems.
