Investigation into the effect of continuous light on zebrafish biology and life cycle is lacking. This study examines growth rate, survival, and generation time of zebrafish raised under continuous illumination (24:0 photoperiod) from the time of fertilization to adulthood. Based on previous experiments in our laboratory with other cyprinid fishes, faster growth rate and shorter generation time under continuous illumination were predicted.
Larviculture methods utilizing rotifers, Brachionus plicatilis, and brine shrimp, Artemia salina, nauplii, were modified for this study. Zebrafish larvae were stocked in aerated stagnant water tanks at 5 days post fertilization (dpf) at a density of 100 larvae/L, which is 10 times higher than previously described. Feeding began at 6 dpf with live rotifers. At 12 dpf, half of the population was transitioned to live brine shrimp nauplii while the other half remained on rotifers for the duration of the study (46-50 dpf).
Fish achieved an average length of 16.1±0.7mm and weight of 61.6±6.7mg at 20 dpf, 2-5 and 10-30 times greater, respectively, than the length and weight described in the literature. Daily growth rate (%) was 39.7% from 12 to 20 dpf. Survival at 12 dpf (7 days post initial feeding), when larvae are most sensitive, was 75.6±10.6%. Once fish reached a size where gender could be visually distinguished (42 dpf), spawning pairs were set up daily (this included dark:light regime, 10:14, for 1-2 days) until a successful spawning occurred. Generation time (from egg to egg) was determined as 44 dpf (when the first pair spawned), 5 days earlier than the shortest generation time reported thus far in the literature (Aoyama et al. 2015. Zebrafish 12:288). This demonstrates that zebrafish can be successfully grown under continuous illumination to produce higher than average growth rate and shorter generation time than that suggested under light/dark regime. Using this method, five consecutive generations have been produced in 228 days. This rearing protocol will drastically reduce the time required for multigenerational experiments and mutant strain development, thereby considerably decreasing the cost of zebrafish culture.