Determining a Suitable Substrate Size and Sampling Frequency for Rearing Juvenile Rainbow Mussels Villosa iris

Abstract

The effects of sampling frequency and substrate size on the overall size and survival of juvenile rainbow mussels Villosa iris were investigated in 4-L round flow-through tanks. All tanks contained either fine sediment (<50 μm), fine limestone sand (500–850 μm), or coarse limestone sand (1,000–2,500 μm) and were sampled every 2 weeks or once at the end of the 10-week experiment. Tanks left unsampled for 10 weeks had 12.8% higher survival regardless of substrate treatment. Juveniles in unsampled tanks also had greater shell length than those in sampled tanks. Juveniles cultured in coarse sand had the best survival in the sampled tanks (36.4%), and juveniles reared in fine sand had the best survival in the unsampled tanks (51.9% at 10 weeks). Analyses of gut contents at 10 weeks revealed that juveniles were consuming large amounts of detritus and algal cells 5–10 μm in size, primarily Coelastrum, Chlorococcum, Chlorella, and Navicula spp. These results show that frequent disturbance of juveniles by sampling may impede physiological functions, resulting in stress and a decrease in overall survival and shell length. It also appears that fine limestone sand (500–800 μm in size) is the best substrate for juvenile culture purposes in similar rearing systems.