Fish convert only a relatively small fraction of the nutrients supplied through feed into biomass, with nitrogen retention efficiencies ranging from approximately 14 to 30 %. In addition, only about 40 % of the harvested biomass in African catfish and up to 60 % in Atlantic salmon is recovered as edible fillet. The remaining fractions, including the head, skin, liver, gonads, and other tissues, are often treated as low-value byproducts despite containing valuable bioactive compounds and nutrients. This highlights the relevance of the nose-to-tail concept as a strategy to improve resource efficiency and promote circularity in aquaculture.

Within this context, the biochemical composition of the liver, gonads, and skin of African catfish, rainbow trout, and pikeperch was investigated to identify potential value-added applications. Possible utilization pathways include nutrient extraction, incorporation into pet food products, and the recovery of compounds with pharmaceutical or biomedical potential. Furthermore, sex-specific differences in the amount and composition of these byproducts were examined to assess whether male and female individuals offer distinct opportunities for valorization.

Preliminary results indicate considerable potential for the further utilization of these side streams, emphasizing their value as resources rather than waste and supporting the implementation of more sustainable and circular aquaculture practices.

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