Finding the sweet spot: The use of dissolved glucose in the commercial rearing of post-settlement Greenshell™ mussels

The widespread and extensive reliance on wild-sourced spat, which are inconsistent in supply and variable in nutritional condition, is a major factor limiting the growth of bivalve aquaculture globally. Producing spat in hatcheries can circumvent these issues, although the costs associated with feeding juvenile bivalves with high-quality cultured microalgae have constrained the expansion of hatchery and nursery production. One promising alternative to reduce reliance on cultured microalgae is to provide dissolved sugars alongside microalgae. This study aimed to determine whether dissolved glucose could be used in the commercial rearing of Greenshell™ mussels in New Zealand hatcheries, specifically during the first two weeks following larval settlement, when microalgal feeding costs are highest. Replacing 10 % of live microalgae with dissolved glucose (100 μg mL −1 ) for 2 h daily resulted in no differences in the growth, microalgae consumption, spat densities (a proxy for survival), or elemental composition of spat when compared with those spat in the 100 % microalgae ration over the 14 day period. Furthermore, supplementing a 100 % microalgae ration with dissolved glucose showed a trend towards greater spat growth without affecting performance. These findings demonstrate that dissolved glucose is an effective feed in bivalve hatcheries to replace or enrich microalgae as the only food. However, further research is needed to determine the most effective combination of dissolved nutrients to meet the precise nutritional requirements of Greenshell™ mussel spat. This will allow commercial operators to choose valuable alternatives to enhance mussel spat growth and hatchery profitability without compromising performance. • 10 % of live microalgae was successfully replaced daily with dissolved glucose (100 μg mL −1 ) with no measurable compromise in spat performance. • Dissolved glucose presents an effective partial replacement to microalgae in commercial Greenshell™ mussel spat rearing. • Additional research into optimal nutrient combinations and replacement levels will optimise cost-savings on microalgae.