Optimization of breeding conditions in Danionella cerebrum to advance its use as a vertebrate model

We systematically evaluated tank configuration and spawning-tube parameters to improve egg production and collection efficiency in Danionella cerebrum. A shallow breeding tank with a black bottom significantly increased egg production while facilitating egg collection. Further optimization of spawning-tube parameters revealed a strong effect of tube diameter on reproductive performance, with narrower tubes improving fertilization efficiency and a 4-mm inner diameter yielding the highest egg production. Longer tubes also tended to increase egg production, although the difference between 5- and 10-cm tubes was not significant. While 5-cm tubes facilitated routine egg collection, the trend toward higher egg production and greater water volume of 10-cm tubes enabled short-term in-tube embryo culture, providing an alternative workflow when frequent egg collection is unnecessary. Notably, increasing the number of available spawning tubes did not further enhance egg production; instead, analysis of tube usage revealed a preference for previously used spawning sites. Together, these findings establish practical breeding parameters that improve reproductive output and streamline egg collection and embryo handling in D. cerebrum.