Introduction
Mariculture is the main source of bivalves globally, but this supply is often limited to a few species. In the Mediterranean Sea, the primary bivalves being farmed are mussels and oysters, which highlights the need to introduce new species. The Mediterranean scallop (Pecten jacobaeus Linnaeus 1758) is a commercially sought-after species mostly targeted by beam trawlers in the northern Adriatic Sea. However, constant fishing pressure has led to decreased landings in recent years. Pecten jacobaeus has a high market value and, according to previous research, can reach market size in just 18 months, with high survival rates, making it a potential candidate for aquaculture. The biggest challenge in farming this species, however, is the lack of a reliable and inexpensive source of seed.
The aim of this study was to investigate the potential for collecting juvenile P. jacobaeus from nature - referred to as wild spat collection - and to monitor their growth in farming installations, specifically lantern nets, for future aquaculture purposes.
Materials and methods
Collectors, which were mesh bags filled with netron filament nets, were deployed each month from a raft at a bivalve farm located in the Krka River estuary, between the fall of 2024 and the summer of 2025. Two types of collectors, differing in mesh size (10 mm and 1 mm) were placed at various depths, ranging from 8 to 20 meters in 2-meter increments. After two months of submersion, the collectors were retrieved and examined for collected juveniles, which were then counted based on collector type and depth. Collected juveniles were measured and then placed in lantern nets at two depths, 8 and 15 m. Each subsequent month juveniles were measured again to estimate their growth. During the experiment environmental parameters, such as temperature, salinity and chlorophyll a, were monitored.
Results
Our results indicate that the collection of P. jacobaeus juveniles from the Krka River estuary was highest during the spring and fall seasons. We observed that collectors with larger mesh sizes captured more juveniles than those with smaller mesh sizes. Additionally, collectors that were positioned at greater depths yielded the highest numbers of collected juveniles, with a decline in numbers closer to the surface.
The growth rate of juveniles was fastest during the spring and fall seasons. We found that juveniles placed lantern nets at lower depth exhibited better growth compared to those placed in lanterns at greater depth, although growth varied among individual juveniles. The survival rate was low overall, with the highest mortality recorded among the smallest juveniles, which decreased as the juveniles grew larger.
Discussion
The collection of juvenile P. jacobaeus from the Krka River estuary coincide with the scallop’s reproductive cycle, as larvae attach to collectors 3-4 weeks after spawning. The highest numbers of juveniles were recorded following the spring and fall spawning periods. Collectors with larger mesh size yielded better results, likely because larvae could more easily enter these collectors, while smaller mesh sized collectors became clogged with fouling. The increased collection of juveniles at greater depths is attributed to the fact that P. jacobaeus is a benthic species; therefore, the highest numbers of larvae are found closer to the bottom.
The faster growth of juveniles during spring and fall can be linked to the optimal temperature conditions and the abundance of available food, which peak during these seasons. Greater mortality rates were observed among the smallest juveniles, as they are most vulnerable to changes in conditions and handling. In contrast, the mortality rate decreased as juveniles grew larger and became more resilient.
Conclusions
Collecting P. jacobaeus spat from the wild is most effective during the spring and fall seasons after spawning occur. Using collectors with larger mesh sizes (approximately 10 mm) and placing them at greater depths results in better juvenile collection. Juvenile growth is rapid but depends on ambient temperature and food availability, and there are high mortality rates during the early stages of development. The number of juveniles typically collected is insufficient for starting commercial aquaculture production, so alternative methods for acquiring juveniles are necessary.
References
Food and Agriculture Organization of the United Nations [FAO] (2022) The State of World Fisheries and Aquaculture (SOFIA) 2022. Towards Blue Transformation. FAO, Rome.
FAO, 2024. Database. Global Aquaculture Production. Fisheries and Aquaculture Division. Rome. https://www.fao.org/fishery/en/collection/aquaculture?lang=en
Shumway, S.E., Parsons, G.J. (2016) Scallops: Biology, Ecology, Aquaculture and Fisheries. Elsevier, Amsterdam.
Marguš, D., Teskeredžić, E. 2005. Attachment of larva, survival and growth of juvenile scallops (Pecten jacobaeus Linnaeus, 1758) in controlled breeding in Šarina Draga bay —mouth of the Krka River. Ribarstvo, 63 (1), 1-14.
Baždarić, B., Peharda, M., Šarić, T., Župan, I., 2018. Growth of the Great Mediterranean scallop (Pecten jacobaeus) in the Novigrad Sea (Croatia). In: Scientific Committee (Eds.) 69th Annual Meeting of the European Federation of Animal Science, Dubrovnik, Croatia. Wageningen Academic Publishers, Wageningen. pp. 295-295.
Clodia database, 2020. Database of Fishery Data from Chioggia, Northern Adriatic Sea. https://chioggia.biologia.unipd.it/banche-dati/