Factors affecting the food value of diatom strains for post-larval abalone Haliotis iris

Abstract

The growth and survival of post-larval abalone Haliotis iris (mean initial shell length 570 μm) fed on eight strains (seven species) of benthic diatom were examined in the laboratory. Post-larvae showed active feeding behaviour on all diatom strains. Two strains ( Achnanthes longipes-1 and Nitzschia sp.) produced significantly faster growth (means 34–35 μm shell length per day) than the remaining six strains (means 11–17 μm/day). The two fast-growth strains were efficiently digested by post-larvae, with 93–94% of live cells ruptured during passage through the gut. Two of the remaining strains could not be ingested during the growth experiment because the cells were too large ( A. longipes-2) or too strongly attached ( Cocconeis pseudomarginata). For the other four strains ( Navicula britannica, Nav. ramosissima, Navicula sp. and Nitzschia ovalis) most cells passed through the gut alive. Survival rate was highest on the two fast-growth strains, and survival was positively correlated with both growth rate ( r=0.73, P<0.05) and digestion efficiency ( r=0.80, P<0.05) of diatoms. The digestion efficiency of diatom strains appears to be an important factor determining their dietary value. Digestion efficiency can be influenced by diatom morphology, attachment strength, frustule strength and post-larval age/size. Isolation and use of digestible strains may improve hatchery culture of abalone.