Arctic charr (Salvelinus alpinus) farming in southern Norway

Abstract

Arctic charr (Salvelinus alpinus) is a stenothermic cold-water fish with a circumpolar distribution. The species features large variations in life history, as populations are anadromous, riverine or lake dwelling. It occurs in various different morphs, which differ in physical traits, such as body size, head shape, and mouth position. The ecological niches of different morphs exhibit great variation as well, e. g. in terms of feeding ecology. Arctic charr has potential as a cultured species, and interest in Arctic charr farming existed since the 1970s. The global production of Arctic charr in aquaculture was between 6000 and 10 000 tonnes in 2013, with all the largest producers located in northern Europe. Arctic charr is suitable for aquaculture, as it grows rapidly at low temperatures, and tolerates high stocking density. Its high fillet yield and amenability to niche markets are also advantageous. However, Arctic charr aquaculture is a relatively small industry, which has made slow progress during its development. Some of the main problems are connected to obtaining viable eggs and juveniles in terms of egg quality, fertilisation rates, and survival through first feeding. There have also been challenges connected to variable growth and flesh pigmentation, early maturation, and marketing. Despite the large volumes of freshwater available in Norway, freshwater fish farming in general, and Arctic charr farming in particular have remained small industries here. One underlying reason are strict environmental regulations connected to freshwater aquaculture in Norway. Parasites may cause harm to Arctic charr aquaculture by reducing growth rates and marketability, as well as causing mortalities in fish held in cages in freshwater. There is little information available on freshwater parasites in southern Norway, as well as parasites threatening Arctic charr aquaculture.

The aim of this thesis is to identify challenges, and propose solutions to problems connected to freshwater aquaculture of Arctic charr in southern Norway. As a general problem in Arctic charr aquaculture, pre-hatch survival has been investigated by reviewing relevant literature about brood-stock management, fertilisation, and egg rearing in aquaculture. A common disinfection protocol for eggs featuring chemical disinfection with formalin before the eyed stage, and hand-picking during the eyed stage, was re-examined. The protocol was tested on fish from a local population in Vestfold and Telemark County. Four different treatments were tested, formalin treatment before the eyed stage only, hand-picking during the eyed stage only, a combination of formalin treatments and hand-picking, and one untreated control group. The hatching percent of these four treatments was compared using a two-way ANOVA. Both formalin treatments and hand-picking increased the proportion of hatched larvae. Hand-picking was more effective, likely because of its timing during the eyed stage. The use of formalin during the entire incubation period is advised until more information on the dynamics of water mould infections is available. Such information allows timing the application of chemical treatments to times of higher infection risk.

To successfully produce offspring of Arctic charr in aquaculture, summer holding temperatures of the brood-stock should be kept low (< 12 °C). Results on the dietary fatty acid composition and its influence on egg survival remain inconclusive. Extensive knowledge has been gained on the timing of spawning, and its manipulation using photoperiod, temperature and hormone treatments. Year round spawning is possible in cultured Arctic charr, and the synchronisation of spawning is important for good egg quality. Suitable routines for fertilisation and egg incubation are being developed, and important factors are the identification of ripe females before spawning, “dry” fertilisation in ovarian fluid, and low incubation temperatures (< 8 °C). There are numerous studies on egg quality parameters, that identify e.g. egg size as important. Egg size is also correlated to female age up to six years. However, not all studies confirm egg size as a suitable quality parameter. Energy density is shown to be more variable in smaller eggs, and may be a better egg quality parameter. Not much information is available on sperm quality parameters, but sperm quality has been identified as limiting factor for reproductive success.

To test conditions for Arctic charr aquaculture in the region, parasites were identified in a southern Norwegian lake, and factors determining their abundance were identified. The lake is located in Telemark and Vestfold County, in a different watercourse than the population of Arctic charr for the formalin experiment. Macro-parasites were identified, and their abundance was modelled in relation to age, length, weight, δ13C, δ15N, C/N-ratio, location, season, and sex in negative binomial generalised linear models. The most prevalent parasites in the investigated host species were determined by the habitat of the host. Arctic charr was the most pelagic species investigated, followed by European whitefish (Coregonus lavaretus) and European perch (Preca fluviatilis), according to stable isotope signatures. The abundance of parasites were most often increasing with increasing age or length of the host, and short-lived parasites exhibited seasonal variations.