Transitioning from algae to clay as turbidity agents: Timing, duration, and transition rates for larval sablefish (Anoplopoma fimbria)

Clay (claywater) can substitute for algae (greenwater) as a turbidity agent after the first week of feeding for larval sablefish (Anoplopoma fimbria), reducing dependence on expensive algae. However, more information is needed to optimize the timing and rate of transition from greenwater to claywater, and to determine whether claywater can be used until the end of the larval period. This study compared four turbidity schedules through the entire 35-day larval period: greenwater transitioned to claywater on day 8, greenwater transitioned to claywater on day 18, greenwater throughout, and claywater throughout. Both gradual and sudden transitions were explored on days 8 and 18. Transitioned larvae, compared to non-transitioned larvae, had lower feeding rates the day after sudden day-8 transitions, but not the day after sudden day-18 transitions, and had lower body weights seven days after sudden day-8 and day-18 transitions. Gradual transitions (over four days instead of one) did not alleviate these negative effects on feeding rates and weight. However, by the end of the larval period, larvae in both transitioned treatments had higher body weight and biomass than larvae from non-transitioned treatments. This suggests that the short-term negative effects on feeding and body weight in transitioned larvae were followed by greater growth benefits. Transitioning at day 8 minimized algae costs, and transitioning at day 18 maximized biomass. Both treatments that transitioned from greenwater to claywater were better than the traditional greenwater-throughout treatment in algal cost savings, biomass, and wet weight per larva. This study provides detailed methods for the use of claywater to further reduce monetary cost and improve production for sablefish aquaculture. •We compared the rearing of larval sablefish (Anoplopoma fimbria) in algae and clay.•Algae (greenwater) is expensive but minimizes larval mortality.•Clay can substitute for algae from the second week to weaning.•There are short-term costs of clay, but these are outweighed by long-term benefits.•Clay improves growth at a decreased cost.