Experiments to culture juvenile freshwater mussels in small tanks, floating containers and sediment beds

Freshwater mussel culture has become an attractive enterprise because of its application for restoring depleted freshwater mussel populations, for rearing adults to support shell and cultured pearl industries, and for environmental monitoring and assessment. This study focused on testing indoor and outdoor culture techniques to rear newly metamorphosed juveniles of the rainbow mussel (Villosa iris). Tanks and floating containers were used outdoors, and sediment beds and floating containers were used in indoor culture experiments.

Culture experiments with indoor sediment beds produced modest growth rates and variable survival rates for up to 4 months. Shell lengths of juveniles increased from 0.38 - 0.41 mm to 0.93 - 3.22 mm, 1.45 - 7.05 times original size; survival rates ranged from 1.27 % to 51.0 %. Experiments with indoor floating containers resulted in an increase of juvenile shell lengths from 0.38 - 0.40 mm to 0.86 - 2.07 mm, an 86 - 207 % increase; survival rates were 23.3 % to 27.0 % after 3 months. All indoor culture experiments combined water flow, inoculation of algae, fertilization, lighting and a pre-operation phase. Experimental results suggested that indoor floating container culture was a useful method to rear newly metamorphosed juvenile mussels, and the indoor sediment bed culture technique may also be suitable with modification, especially if filamentous algae can be controlled. Both outdoor tank and floating container culture experiments yielded poor results, which were probably caused by unsuitable culture conditions.

Differences in juvenile growth rates (P < 0.001) and survival (P < 0.001) between floating container experiments I and II, which used the same culture techniques, were attributed to differences in culture conditions; water temperature (P < 0.001), dissolved oxygen (P < 0.01) and hardness (P < 0.01). Water temperature also contributed to a higher growth (P < 0.001) and survival rate (P < 0.001) in sediment bed culture II. The extensive occurrence of filamentous algae on sediments affected results and caused lower growth (P < 0.001) and survival rates (P <0.001) of juveniles in the sediment bed culture experiment III, IV and V. Finally, absence of water flow may have influenced growth and survival of juvenile V. iris, a naturally riverine species. Lack of currents near the bottom of tank and floating containers where juveniles resided likely contributed to complete mortality of juveniles in the outdoor culture experiments.