Introduction
Copepods are increasingly explored as a source of live feed for larviculture, yet not all copepod species seem equally suitable. Previous studies have shown that digestibility differs strongly among copepod species, with potential consequences for larval growth and survival.
Benthic copepods offer practical advantages for larviculture, such as favourable fatty acid composition, resilience to environmental variation and short reproduction cycles, allowing for higher harvesting rates. However, adaptation to benthic habitats often involves the development of thicker cuticles to withstand coarse sediment, which may reduce digestibility for fish larvae.
Materials and methods
In this study, we developed an in vitro assay that allows quantitative evaluation of digestibility of multiple benthic copepod species using the enzymes trypsin and lipase. Experimental species were chosen based on culturability and their ecological relevance in the estuarine benthic food web. Artemia franciscana nauplii were included as a reference. Complementary analyses of total protein content were performed to broaden the nutritional assessment. In addition, the fatty acid composition of all species was analysed using gas chromatography coupled with mass spectrometry (GC-MS). Protein content, digestibility, and fatty acid data were integrated into a multi-trait ranking system to evaluate the overall nutritional quality of each species.
Results and discussion
Total protein content varied significantly among species (one-way ANOVA, F4,10 = 32.93, p < 0.001), with M. littorale reaching the highest protein content (47.0 ± 1.6% dry matter) and N. spinipes the lowest (21.7 ± 3.5%). In vitro protein digestibility also differed significantly among species (F4,18 = 11.41, p < 0.001), with A. franciscana and D. palustris showing the highest digestibility and N. spinipes showing negligible digestibility, consistent with the absence of a systematic enzyme effect in this species. Notably, protein content and digestibility were not correlated: M. littorale combined a high protein content with one of the lowest digestibilities, indicating that a substantial fraction of its protein is not bioavailable to fish larvae, and that neither parameter alone is sufficient to rank species for nutritional quality. Fatty acid analysis (GC-MS) further showed that T. discipes and M. littorale were richest in DHA, while D. palustris contained the highest EPA levels; N. spinipes consistently ranked poorly across nutritional indicators. Integrating protein content, digestibility, and key fatty acid ratios (DHA:EPA, ARA:EPA, n-3:n-6, PUFA:SFA) into a multi-trait ranking revealed that no single copepod species performed favourably across all indicators, reflecting trade-offs between protein and lipid quality traits. These results highlight the added value of a multi-parameter approach for selecting suitable live feed candidates in marine fish larviculture.
Acknowledgement
This research is conducted using infrastructure funded by EMBRC Belgium - FWO international research infrastructure I000825N. The first author acknowledges a Blue Growth PhD grant from UGent BOF (Special Research fund). Research is supported by the Blue Growth Research Lab in Ostend Science Park. We acknowledge the collaboration between the Faculty of Bioscience Engineering and the faculty of Sciences at Ghent University.