VIABILITY OF INTACT, PRE-KILLED ROTIFERS AS AN ALTERNATIVE FIRST FEED FOR ZEBRAFISH Danio rerio FRY
Rotifers (Brachionus plicatilis) are an important first-feed item for zebrafish fry due to their enticing motility, gutloading capacity , and small culture footprint . Although larval fish benefit from feedings, the process for culturing rotifers can be laborious and is periodically prone to collapse which can impede survival and growth of newly hatched fry. To minimize labor costs , we wanted to see if pre-killed, enriched rotifers could yield comparable or better survival for zebrafish fry.
Wild-type zebrafish (AB and TL) were spawned to produce an F1 generation of AB and TL hybrids (ABTL). Embryos were collected and placed in 20mL of E3+MB embryo media at a density of 60 embryos/tissue culture dish and maintained at 28oC. They were inspected twice daily and received a 50% media exchange and removal of dead embryos and detritus. Fry were supplied with food daily following inflation of the swim bladder at 5dpf and transferred to polycarbonate tanks at 7dpf . Water parameters remained constant for all fish (Table 1) with no detectable levels of ammonia or nitrite. Nitrate levels were kept below 10ppm. Fry were fed prescribed diets (Table 2) to satiation three times daily with only two feedings on weekends. At 15dpf , fry received 48hr. brine shrimp and, if able to consume it, replaced their first feed diets with thrice daily feedings of brine shrimp and Gemma 75. Mortality rates and time to maturation were recorded for each feeding regime.
Preliminary findings indicate fry initially fed a mixture of Roti-Feast and Gemma 75 had comparable survival to those fed live rotifers, with both groups surpassing those fed only on Gemma 75. The lack of food motility did not hinder palatability for fry. T he use of Roti-Feast required less overall cleaning and daily colony maintenance versus the use of live rotifers. Overall, using whole, pre-killed prey items may provide facilities with labor and cost savings in addition to an equally effective first feed alternative to live prey. Future studies should follow fry fed pre-killed diets through ontogeny and investigate any potential skeletomuscular deformities, fecundity problems, and life expectancy versus standard feeds.
