Invasive Species Compendium

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Abstract

Preparation and assessment of microalgal concentrates as feeds for larval and juvenile Pacific oyster (Crassostrea gigas).

Abstract

We assessed a flocculation method for preparing concentrates of seven microalgae. For five of these (Chaetoceros calcitrans (C.CAL), C. calcitrans forma pumilum (C.CAL(PUM)), Chaetoceros sp. ("tenuissimus-like") (C.TEN), Skeletonema costatum (SKEL) and Isochrysis aff. galbana (T.ISO)) we assessed flocculates as an 80% diet component in four experiments with larval and one with juvenile Pacific oysters. The remaining 20% diet component was T.ISO, except in Experiment 2 for larvae, where C.CAL(PUM) was used. The flocculates had been stored at 4 °C for 9-21 days and were compared against the corresponding fresh microalgae. For larvae (initial size, 74-82 µm), best growth was usually seen in diets containing C.CAL(PUM). In Experiment 1, larvae fed an 80% C.CAL(PUM) (live) diet increased to 248 µm after 16 days. This growth was ≥50% more than with diets containing C.CAL(PUM) (concentrate) or C.CAL (live or concentrate). In Experiment 2, larvae fed C.CAL(PUM) (live) as the 20% basal ration (control) grew to 167 µm. Supplementation of this diet with live or concentrated T.ISO as the 80% component did not improve larval growth. In Experiment 3, larvae fed an 80% C.CAL(PUM) (concentrate) diet grew as well as larvae fed the 80% C.CAL(PUM) (live) diet (192 and 194 µm, respectively) and more than larvae fed 80% C.TEN (live or concentrated; 155 and 162 µm, respectively). In Experiment 4, larvae fed 80% live SKEL diet (125 µm) grew more than larvae fed SKEL (concentrate) or C.CAL (live or concentrate) (larvae, 104-112 µm). Over all experiments, larval survival ranged from 2% to 90% and was reflected in changes observed for larval growth. For juvenile oysters, a basal 20% T.ISO diet alone gave moderate growth after 28 days (k=0.031 day-1). Supplementation with a SKEL concentrate improved growth (k=0.054 day-1), whereas supplements of live or concentrated forms of either C.CAL(PUM) or C.TEN gave the best growth (k=0.083-0.090 day-1). This study demonstrated that flocculated concentrates of microalgae, especially C.CAL(PUM) or C.TEN, can be used effectively as major dietary components for larval and juvenile oysters.