Polychaetes as aquaculture feed: feeding experiments and nutritional value analysis of Eurythoe spp.

Abstract Aquaculture needs more environmentally friendly alternatives to fishmeal-based feed. Polychaetes could be part of a solution, since they are comparatively easy to cultivate. Eurythoe sp. and especially the species complex Eurythoe complanata is widely distributed across tropical coasts and aquaria. However, studies on the biology, needed for a targeted cultivation, are rare. In order to evaluate the species’ potential as an aquaculture species, an understanding especially of their feeding preferences and proximate composition, namely lipid, carbohydrate and protein content, is essential. Here, we present a—to the best of our knowledge—first adapted protocol to quantify lipid, carbohydrate and protein content in Eurythoe spp., as well as a comparison of female and male individuals of two species of the genus, referred to as spec. 1 (E urythoe cf. complanata ) and spec. 2 ( Eurythoe sp.). Overall, the values of the lipid content ranged between 7 and 13% of the dry weight (DW) with the male polychaetes of spec. 1 showing lower lipid concentrations compared to the other species. Additionally, the male polychaetes showed higher carbohydrate levels than females or individuals of the other species. Carbohydrate concentrations between 3 and 10% DW were measured. The protein content of all specimens was between 27 and 37% DW. A 90-day feeding experiment revealed highest specific growth rates (SGR) of the group fed with a control of pellets, compared to algae commercially available as fish feed and spinach. Spontaneous fragmentation, known as a form of asexual reproduction among annelids, occurred over the experimental run. Despite the revealed high potential as a feed source for aquaculture purposes, more detailed investigations are necessary, especially regarding the targeted feeding and potential complications due to their venom.