Influence of stocking density on growth of mussels (Mytilus galloprovincialis) in suspended culture

Crowding conditions in bivalve populations cause intraspecific competition processes, resulting in individual growth reduction. In aquaculture, density is usually maximized to obtain a greater commercial yield. Commercial farms provide an ideal scenario for studying the effect of density on mussel growth in suspended culture systems. In this study, different growth indicators for Mytilus galloprovincialis (growth rates, length and weight growth curves and size frequency distributions) were measured along a cultivation density gradient. Ropes cultured at different densities (220, 370, 500, 570, 700, 800 and 1150 ind/m) were hanged from a commercial raft and growth indicators were monitored monthly over the second phase of traditional culture in Galicia, from thinning-out to harvest (April to October 2008). A negative effect of density on individual growth was observed. Individuals cultured at lower densities presented higher growth rates and consequently reached greater weight and length values at the end of the experimental period than those cultured at higher densities. Differences in growth related to the cultivation density may suggest differences in intraspecific competition for limiting resources (space/food). Effects of density on growth started after 4 months of culture (August) when individuals reached sizes around 66 ± 1.3 mm. The increase in size of individuals in a population implies an increment of their food and space requirements, which in turn intensifies intraspecific competition. This fact should be considered in aquaculture management, since higher densities could be supported without effects on growth performance if cultured mussels are limited to a lower size.

► Mussel growth was measured along a cultivation density gradient in suspended culture.
► A negative effect of high culture density on individual growth rates was observed.
► Mussels grown at lower densities reached greater asymptotic weight and length values.
► Differences in growth related to culture density suggest intraspecific competition.
► An increased effect of intraspecific competition with mussel size was observed.