Isolation of new nanoplanktonic diatom strains and their evaluation as diets for juvenile Pacific oysters (Crassostrea gigas)

Abstract

Ten new diatom strains were isolated from coastal waters of Australia and their potential as feed species for aquaculture evaluated based on their cell size, division rate and biochemical composition. All strains were within the size range ingested by most filter feeders, i.e. 3–10 μm. Cellular growth rates of aerated 1.6-l cultures ranged from 0.5–0.7 divisions·day−1 (Papiliocellulus simplex CS-431, Nitzschia cf paleacea CS-433) to 1.7–2.0 divisions·day−1 (Attheya septentrionalis CS-425, Entomoneis cf punctulata CS-426, Extubocellulus spinifera CS-428, Thalassiosira oceanica CS-427). The latter four strains were also rich in energy storage fractions (carbohydrate and/or lipid), especially as cultures progressed to stationary phase.

Based on the initial screening, A. septentrionalis, E. cf punctulata, E. spinifera and T. oceanica were assessed as to their food value for juvenile Pacific oysters. The diatoms were fed as part of a mixed diet—each making up 70–83% of the total dry weight—together with an equal mixture of the haptophytes Pavlova lutheri and Isochrysis sp. (T. ISO) over a 21-day experiment. Diets containing A. septentrionalis and E. cf punctulata were the most effective, producing growth rates (k=0.050 day−1) marginally inferior to a similar (reference) diet containing a commonly used aquaculture diatom strain of high nutritional value, T. pseudonana CCMP 1335 (k=0.055 day−1). Regression analysis showed that oyster growth rate was correlated with the content of protein in the equal ration algal diets.

We have shown A. septentrionalis and E. cf punctulata to be alternative Australian strains with good nutritional value that could be utilised by oyster hatcheries or nurseries. These strains, and others isolated in the study with different characteristics such as benthic growth or high protein levels, could also prove useful feed species for other animal species grown in aquaculture such as abalone and scallops.