Effects of food abundance on juvenile freshwater mussel survival and growth in aquaculture, and comparison with growth in streams

Captive propagation has become an important tool in the conservation of imperiled freshwater mussels. Previous studies provide conflicting results about the effects of food abundance on survival and growth of juvenile mussels in aquaculture, and the extent to which growth in the hatchery reflects growth in the wild is unknown. We evaluated the effects of abundance of an algal-based diet on survival and growth of juvenile Cumberland Bean (Venustaconcha troostensis) in a recirculating aquaculture system. We compared food abundance (as fine particulate organic matter, FPOM) in our experimental food rations with FPOM in 14 streams to assess the similarity of hatchery and natural food sources. We compared growth in our experiments with previously published growth estimates of Cumberland Bean at 17 stream sites. Growth in the hatchery increased linearly with increasing food abundance from 3.5 to 27.6 mg/L algal dry mass (about 111,000-1,147,225 cells/mL), and mussel size after two weeks increased 2.9% for every doubling of algal dry mass within the range of our experimental rations. We observed no negative effects of increasing food abundance on survival, and ammonia concentrations remained below chronic effect concentrations in all treatments, even in food rations much higher than recommended by previous studies. FPOM in our experiments spanned a similar range of values as FPOM in streams. Growth in our experiments was similar to growth in streams, but our experimental temperatures were higher than in streams. When the probable effect of temperature was accounted for, growth in most experimental food rations was substantially lower than expected in streams despite similar FPOM. This suggests that food quality or other conditions are more favorable for mussel growth in the wild.