European eel larviculture: First establishment of feeding leptocephalus culture.

Abstract

Anguillid eels are targeted, high-value species for aquaculture in Asia and Europe. Unfortunately, eel farming is still capturebased, exclusively relying on wild-caught glass eels and thus, the sustainability of this industry is challenged by the present critically low stock abundance, which is especially the case for European eel, A. anguilla (Pike et al., 2020). Hence, it is urgently needed to further develop and establish captive breeding techniques and technologies for this critically endangered fish species. Advances in Japanese eel culture (Okamura et al., 2013) have formed the baseline for eel research, promoting recent development of hatchery protocols for European eel (Tomkiewicz et al., 2019). While offspring culture techniques for the European eel encompass the endogenous feeding stages (Sørensen et al., 2016), the transition to exogenous feeding is still challenged by lack of insights regarding the feeding stages and dietary requirements for the unique leptocephalus larvae. Research has been conducted to identify natural eel larval feeding sources (Miller, 2009) and physiology (Knutsen et al., 2021), but despite increasing knowledge on larval feeding ecology, the natural first-feeding regimes of Anguillid pre-leptocephali remain an enigma. Scientific inquiry has focused on identifying potential first-feeding diets with the first exogenously feeding experiments of hatchery-reared European eel larvae only recently attempted (Butts et al., 2016; Politis et al., 2018), in combination with enhanced rearing techniques aiming at improving larval survival (Tomkiewicz et al. 2019; Politis et al., 2021). In continuation of this work, research in the innovation project ITS-EEL has focused on developing prototype diets, exploring feeding and gut-priming regimes as well as testing larviculture procedures by applying progressively advancing culture techniques and technology. The presentation will overview these progressive advancements regarding the requirements of larval European eel in terms of abiotic (such as temperature, salinity, light, pH) and biotic (such as gut-priming, feeds, feed amounts, feeding regimes, microbial control, water quality) factors, from a morphological and molecular point of view.