In recent years, mariculture has become the largest market supplier of bivalves, but this offer is often limited to a small number of species, so there is an increasing need for introduction of new species into the aquaculture. The Mediterranean scallop Pecten jacobaeus (Linnaeus, 1758) is the largest bivalve of the Pectinidae family that lives in the Mediterranean and Adriatic Sea. Due to its size, fast growth, and high market demand, P. jacobaeus seems like a potential aquaculture candidate. Greatest challenges for farming of this species are the lack of seed from nature, so to overcome this obstacle, the solution lies in producing the seed in hatcheries.
For this purpose, we conducted a study on the conditioning of P. jacobaeus broodstock under hatchery conditions for its possible preparation of spawning. The broodstock, collected from nature, was acclimatized in the hatchery for 10 days at 15 °C and salinity of 35. Afterwards, it was separated in two groups that were fed with two different types of feed in the amount of 3% of their total dry soft tissue mass. First group was fed with live algae Isochrysis galbana and the second group with concentrate of frozen algae consisted of species Tetraselmis sp., Thalassiosira weissflogii and Thalassiosira pseudonana. Before and 21 days after feeding started, specimens were collected from tanks for the calculation of physiological indices. Shell was separated from soft tissue, which was further dissected for gonads, muscle, and the remaining soft tissue. Total mass of the shell and soft tissue was measured, in wet and dry weight (g), after processing in the dryer at 60 °C for 48 h. Condition index (CI), gonadosomatic index (GSI) and muscle index (MI) were calculated by following methods:
CI= total soft tissue dry weight (g)/shell dry weight (g) x 100,
GSI= gonad dry weight (g)/ total tissue dry weight (g) x 100,
MI= muscle dry weight (g)/ total tissue dry weight (g) x 100.
The results indicate that the conditioning gives good results with both types of feed. The group fed with live feed had higher CI than the group fed with concentrated frozen feed, which can be prescribed to the fact that the bivalves prefer live feed. The group fed with concentrated frozen feed had higher GSI than the group fed with live feed, which can be prescribed to the fact that the feed which consists of more than one algae species promotes better gonadal development, but also to the fact that remaining soft tissue declined in weight. MI showed a slight decline in both groups, which can be attributed to the utilization of the muscle reserves for supporting gametogenesis.
Obtained results suggest that the best results could be achieved with the live feed that consist of more than one algae species. These results will be improved upon so to induce controlled spawning under hatchery conditions in the future.