Åsa Strand

Summer mortalities and detection of ostreid herpesvirus microvariant in Pacific oyster Crassostrea gigas in Sweden and Norway

The Pacific oyster Crassostrea gigas has recently expanded its range in Scandinavia. The expansion is presumably a result of northwards larval drift. Massive settlements were recorded in many areas along the Swedish west coast and southern Norway in 2013 and 2014. After the spawning season in 2014, the temperature of the surface water peaked at 24-26°C. After this period, high and sudden mortalities occurred in a Swedish hatchery and in wild populations along the Swedish west coast and south coast of Norway. Surveys and collected data showed that mortalities mainly occurred during 3 wk in September. All size classes were affected, and affected populations displayed a patchy distribution with heavily affected and unaffected populations in close proximity. Flat oysters Ostrea edulis and blue mussels Mytilus edulis were unaffected. Ostreid herpesvirus (OsHV) was detected in moribund Pacific oyster spat as well as in surviving adults. The virus was identified as OsHV-1 μvar. This is the first detection of this variant in Scandinavia, showing that OsHV-1 μvar is present in areas with recent establishments of Pacific oysters, and where there is no aquaculture of this species.

Genetic analysis of goldsinny wrasse reveals evolutionary insights into population connectivity and potentialevidence of inadverent translocationvia aquaculture.

Eeva Jansson*, Mar ıa Quintela, Geir Dahle, Jon Albretsen, Halvor Knutsen, Carl André, Åsa Strand, Stein Mortensen, John B. Taggart, Egil Karlsbakk, Bjørn Olav Kvamme, and Kevin A. Glover Institute of Marine Research, PO Box 1870 Nordnes, 5817 Bergen, Norway Institute of Marine Research Flødevigen, 4817 His, Norway Centre for Coastal Research, University of Agder, 4604 Kristiansand, Norway Department of Marine Sciences-Tj€arnö, University of Gothenburg, 45296 Strömstad, Sweden School of Natural Sciences, Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, UK Institute of Biology, University of Bergen, PO Box 7803, 5020 Bergen, Norway

Growth and Energy Expenditures of Eurasian Perch Perca fluviatilis (Linnaeus) in Different Temperatures and of Different Body Sizes

To calculate the theoretical daily energy requirement of fish, information about the daily growth increment and the amount of digestible energy needed (DEN) to obtain one unit of biomass gain is required. The thermal unit growth coefficient (TGC) can be used for estimation of the daily growth increment. TGC is thought to be less affected by body size of the fish and temperature than the specific growth rate (SGR). However, there are some indications that the TGC may not be as stable as previous studies have shown. Furthermore, according to the theoretical background, DEN should increase as fish body size increases and with temperature. However, some data indicate that the DEN for percid fish may be unaffected by both these factors. The main objectives of this study was to estimate the effects of temperature and fish body weight on growth (TGC and SGR) and digestible energy need (DEN) of the Eurasian perch Perca fluviatilis (Linnaeus). In two separate laboratory experiments, feed intake, growth and energy expenditures were measured at either different temperatures (8.5-27.1oC) or for fish of different body sizes (20-110g). TGC and SGR proved to be affected by temperature and body size of the fish, while DEN was only affected by body size. The advantages with TGC for growth model construction thus seem to be less apparent than earlier believed. Thus, for evaluation of the theoretical daily energy requirement of fish, a growth model including both temperature and body size of fish, and an energy expenditure model including body size of fish is required.

The Energy Requirements of Percid Fish in Culture

In commercial aquaculture, knowledge about and means for predicting growth rates, feed intake and energy requirements of the farmed animal in different conditions is essential for the viability of the enterprise. As percid fish species are relatively new in culture, there are no models available to estimate the energy requirement of the cultured fish, which in turn limits the opportunities to calculate the required daily feed allowance. Classical bioenergy budgets are often used to describe energy intake in relation to different energy expenditures of fish by quantifying steps where energy expenditures occur. However, in commercial aquaculture the objective is to optimize the output (growth) in relation to the energy intake, e.g. where energy expenditures occur is less important. In this chapter, we put together data from the scientific literature to produce an alternative model for prediction of the daily growth and energy need of percid fish in general and Eurasian perch (Perca fluviatilis L.) in particular. A practice for calculating the daily feed allowance is presented where local rearing conditions can be taken into account. This makes the model applicable to commercial enterprises and may improve feed management, fish growth and thus economics of the fish farms. This chapter also discusses how factors such as season and culture conditions influence the energy requirements and energy expenditures of the percid fish.