Feeding Larval Zebrafish: Small Predators, Big Choices.

Zebrafish husbandry regimens often use live rotifers or paramecia during the first 2 weeks of larval feeding. The rationale is that the small larval gape requires suitably small prey. As larvae grow, they are transitioned to feeding on larger prey in the form of brine shrimp (Artemia). Typically, the Artemia used are the San Francisco Bay (SFB) strain. This strain is reported to be smaller than the Great Salt Lake (GSL) strain and is presumably easier for larvae to capture. Here, we tested the ability of zebrafish larvae to capture either strain. Daily, from 5 to 15 days post-fertilization (dpf), intestinal contents were imaged through the body wall of live larvae following shrimp feeding. Larvae showed increased capture success day by day, and by 9 dpf most larvae captured the SFB strain. By contrast, few larvae captured the GSL strain throughout the study. Morphometric tests comparing the strains showed no differences in length or width for newly hatched shrimp. However, after 48 h of culturing, the GSL strain was significantly larger than the SFB strain. For husbandry regimens that omit rotifers or paramecia and introduce shrimp from the first feeding, these results highlight the importance of using newly hatched SFB Artemia.