Effects of rearing temperature manipulation on oocyte maturation progress in Japanese eel

Published source details Tanaka T., Adachi S., Nomura K., Tanaka H. & Unuma T. (2021) Effects of rearing temperature manipulation on oocyte maturation progress in Japanese eel. Fisheries Science, 87, 681-691.
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This study is summarised as evidence for the following.

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Breed eels in captivity

A replicated study (year not stated) at a research facility in Japan (Tanaka et al. 2021) found that artificially fertilized Japanese eel Anguilla japonica eggs had variable hatching rates in each of two experiments, and rearing females at different temperatures had no effect on hatching rates of their eggs. Average hatching rates were 1–36% in the first experiment, and 29–80% in the second. In both experiments, average hatching rates of eggs from females reared at different temperatures did not differ significantly (experiment 1: 20°C = 36%, 20/15°C = 22%, 15/20°C = 11%, 15°C = 1%; experiment 2: 20°C = 43%, 20/15°C = 80%, 15/20°C = 29%, 15°C = 67%). In each of two experiments, female eels were reared at four water temperature treatments for three days prior to receiving a hormone injection (17α-hydroxyprogesterone) to induce ovulation (20°C for three days, 20°C for two days then 15°C for one day, 15°C for two days then 20°C for one day, 15°C for three days). All eels received weekly salmon pituitary extract injections for 10–17 weeks prior to treatments. Treatments were assigned randomly (experiment 1: 14 eels/treatment) or according to maturation stage (experiment 2: 2–24 eels/treatment; see paper for details). Eggs were collected from ovulated females, artificially fertilized with sperm from captive males and incubated in petri dishes or microplates at 25°C. Hatched larvae were counted three days after fertilization.

(Summarised by: Anna Berthinussen)