Effect of live-storage period and temperature on oxygen consumption rate in the cold-water sea cucumber Parastichopus tremulus

Sea cucumbers are of great significance in marine ecosystems all over the world. The red sea cucumber Parastichopus tremulus is also considered commercially interesting but very little information is available on its ecology and physiology. This study aimed at investigating this North Atlantic species` oxygen demand in relation to live-storage period and temperature in an attempt to deliver some physiological puzzle pieces useful in a potential aquacultural context. Oxygen consumption rate (OCR) was measured in P. tremulus stored in a flow-through system for up to one year, and in recirculation systems at different temperatures (4, 8 and 12°C) for up to four weeks. Throughout the experimental period, biometric data were collected from the different treatment groups and a condition index (CI) calculated. The results showed that long-term storage affected OCR and CI, which increased and decreased with time, respectively. Storage at 4°C resulted in significantly lower OCR and higher CI compared to 8 and 12°C after four weeks, suggesting that 4°C may be best for maintaining body mass during short-term storage, whereas storage at 8 and 12°C may require supplementary feeding to avoid biomass loss. Data presented in this study may be useful for a range of applications, for example in a prospective aquaculture setting, for optimizing live seafood storage, but also for impact assessment and management of wild stocks

Effects of environmental conditions on culturing scallop spat (Pecten maximus)

The great scallop, Pecten maximus, is a valuable bivalve species attractive for human consumption. Scallop aquaculture is increasing, but availability of spat is a bottleneck to the development of a viable culture industry in many countries. The collection of P. maximus spat from the wild has been insufficient, and intensive hatchery production is considered an optional strategy for a predictable spat supply to growers in Norway. Large variations in growth and survival during the post-larval stages are experienced, and temperature, salinity and food availability have been identified as critical environmental factors during the nursery growth stage. A nursery bridges the gap between intensive culture in the hatchery and growout in the sea, and covers the rearing from metamorphosis (ca. 0.25 mm) until the commercial spat size of 15-20 mm. Transfer between production stages and grow-out sites is required in scallop culture. The present study filled an information gap related to effects of environmental factors on small scallops (ca. 2 mm) in the transition phase between hatchery and nursery. Different transfer strategies were investigated to test the capability of scallop spat to tolerate transfer and adapt to new environmental conditions. Experimental studies with hatchery reared P. maximus showed that viability through the various spat stages could be improved by employing adequate culture and transfer strategies. Transfer of spat of different settlement age to nursery was approved to further increase the spat yield. Site selection and timing of transfer are of major importance, and the observed suboptimal and lethal environments should be avoided. Higher rearing temperature (18 vs. 15 °C) resulted in increased growth and survival, while salinity of 20 and 25 affected growth, survival and byssal attachment negatively. Exposure to low temperatures was a main factor affecting the performance of small spat. Acclimation of 1-2 mm spat to a lower temperature than in the hatchery improved post-transfer survival to seawater of <7 °C. So did transfer of larger (4 mm) spat. Alternatively, spat could be transferred to a land-based nursery using solar heated and fertilised “poll” water as food source to give an earlier start of the production season in the spring. The growth was similar to in sea-based nursery. Dry transportation of small spat was shown feasible up to 12-24 hours. The change to "poll" food conditions resulted in a significant decrease of lipids, but except for sterol content, the nutritional status at transfer was not associated with growth and survival in the land-based nursery. Increased water recirculation rates in the hatchery rearing tanks hardly affected the spat performance and the chemical composition, thus supporting more efficient utilisation of algae

Metabolic rate of blue mussels (Mytilus edulis) under varying post-harvest holding conditions

The mussel (Mytilus edulis) is successfully grown in aquaculture in Europe. Mussels are usually sold live and wet storage is becoming more common. In this study, oxygen demand and ammonia excretion were assessed at increasing water temperatures and different post-harvest situations. This information was used to calculate minimal flow rates per unit biomass of live mussels sufficient to keep oxygen above 5 mg L-1 or 50% saturation, and avoid accumulation of ammonia in commercial wet storage. In this study, rope-grown mussels were kept out of water for 8 h to simulate harvesting conditions and then re-immersed in holding tanks at 5, 10 and 15 °C. Oxygen and ammonia concentrations were measured immediately after mussels were re-immersed (0 h), after 6 h and then every day for 3 days. After this period, the mussels were again kept out of water for 48 h to simulate long-distance transport and once again re-immersed for the same period as before. In the first 6 h after re-immersion, the oxygen consumption was between 7.5 and 12.2 μmol g-1 h-1 (dry flesh) and after this period it decreased to a standard level of around 4.0 ± 0.9 μmol g-1 h-1 and was independent of temperature. There were no major differences in oxygen consumption between mussels having spent 8 and 48 h out of water at any of the subsequent water temperatures used for re-immersion. In contrast, the ammonia excretion showed greater differences according to temperature and time out of water. Ammonia excretion was lowest at 5 °C (<0.01 μmol g-1 h-1). The implications of these results for the industry and authorities are discussed considering the water flow rate, depuration specifications and energy costs

Improving scallop (Pecten maximus and Placopecten magellanicus) spat production by initial larvae size and hydrodynamic cues used in nursery system

There are several factors affecting scallops during the metamorphosis process that could explain the relatively low post-larvae yield observed in hatcheries. Competent bivalve larvae respond to different settlement cues to undergo metamorphosis and without adequate cues, larvae delay their metamorphosis. The objective of this study is to improve the settlement ratio of the two scallop species, Placopecten magellanicus and Pecten maximus by physical cues associated with hydrodynamic conditions, stocking density in settlement units and larval size at time of transfer to settling units. For each treatment, physiological condition was determined by fatty acid analysis to determine the energetic reserves and structural lipids. We observed similar results for the two important commercial pectinid species and validate the hypothesis on the positive effect of increased flow rate and larval size after transfer to settlement systems on settlement success. Increasing flow rate also affects positively the physiological condition of settled post-larvae by a higher accumulation of total fatty acids in neutral lipid fractions. Furthermore, no effect of larval stocking density until 90 larvae cm−2 in the downwelling sieves was observed. To our knowledge this study is the first to characterize the effect of seawater flow rate on settlement success of different pectinid species cultured under similar conditions. The experiments were performed in a close to commercial scale and thus are relevant to industry situations