Newsletter January 2025

Step-by-step improvements

In the second half of 2024, we took further steps to improve the growth and survival of eel larvae. Our main focus was on the survival of the juvenile stages (up to 42 days), as this is where most gains can be made. Pre-larval survival (0 to 14 days after egg hatch) averaged 26% over all of 2024, nearly double that of 2023 (14%). The average is heavily influenced by a poor batch in summer 2024. Figures were better in the third and fourth quarters (24 to 42%). Continued adjustments to the culture protocol and less labor-intensive treatment of the tanks allow us to do more parallel experi-ments in the last six months, increasing the chances of a breakthrough.
The survival of young larvae (14 to 42 days) also improved, from an average of 17% in 2023 to 22% in 2024. We pay less attention to improvement of the average egg hatching rate at the moment, because if we increase the rate, we have too little space to use the large numbers of larvae in experiments. We consider this step not crucial because we have also reached 80% at times (target is 90%).

Once the larvae reach the leptocephalus stage, the survival rate increases significantly; we can now culture larvae to almost 300 days, but growth does not continue. The graph shows that length growth is initially 0.14 mm per day, but later flattens out. The target is 0.2 mm per day, up to 6 cm. The diet of the lepto-cephalus is probably crucial. We are trying to solve this problem with a grant from the European Maritime, Fisheries and Aquaculture Fund awarded in October 2024. In doing so, we are cooperating (under strict confidentiality) with specia-lists in fish nutrition from the Aquaculture and Fisheries Group of Wageningen University.