Effects of greenwater and claywater regimes on early exogenous feeding in larval sablefish (Anoplopoma fimbria)

Marine fish larvae often survive better with algae in their rearing water, but algae is expensive and cheaper alternatives should be explored. This study tested the effects of algae and clay, a less-expensive water additive, on feeding, growth and survival during the first week of exogenous feeding in sablefish (Anoplopoma fimbria). After three days with algae or clay, larvae with algae fed better than those with clay. On the fourth day, half of the algae tanks were transitioned to clay, and half of the clay tanks were transitioned to algae. When the transition was 90 % complete, feeding was better if algae was used for the first three days, regardless of whether the larvae were transitioning to clay on day-4 or kept on algae, so the previous water additive (algae or clay) predicted feeding rates better than the additive at the time of the feeding trial. Benefits of the first three days with algae did not last indefinitely, however, as larvae that transitioned from algae to clay on the fourth day stopped showing feeding benefits by the fifth and sixth days. In a separate experiment, different algae-clay mixtures were compared: i) 100 % clay, ii) 25 % algae / 75 % clay, iii) 50 % algae / 50 % clay, and iv) 100 % algae. The third and fourth treatments fed and survived better relative to the first treatment, and did not differ from each other. In another experiment, larval feeding was higher in 100 % algae than in 50 % algae / 0 % clay, highlighting the importance of the clay component of the 50 % algae / 50 % clay mixture. Thus, algae use during the first week of exogenous feeding was halved by using an algae-clay mixture, without impacting larval feeding, growth, or survival. This study provides methods to reduce the reliance on expensive algae during the larval period.