Gadoid mariculture: development and future challenges

This special volume results from the ICES symposium on Gadoid Mariculture: Development and Future Challenges held outside Bergen at Os, Norway, from 13 to 16 June 2004. The symposium was hosted by the Institute of Marine Research and co-sponsored by the Research Council of Norway, the National Oceanic and Atmospheric Administration, USA, and the Department of Fisheries and Oceans, Canada. A total of 181 participants, including students, attended the three-day conference, and represented Nordic countries (Norway, Iceland, Denmark, Faroe Islands, and Sweden), Canada, UK, USA, Spain, Ireland, Russia, Germany, the Netherlands, Poland, and Belgium. The symposium targeted the cultivation of gadoids (cod Gadus morhua, haddock Melanogrammus aeglefinus, pollack Pollachius spp., and hake Merluccius spp.). This theme has not been considered at an international symposium since the symposium The Propagation of Cod (Dahl et al., 1984) was held in Arendal, Norway, in June 1983. The 1983 symposium marked the centenary of IMR Flødevigen Biological Station (originally called the Flødevigen Hatchery) founded by Captain Dannevig and members of the local population for the purpose of producing and liberating cod yolk-sac larvae into the sea and thereby, it was hoped, increasing local stocks (Solemdal et al., 1984). Parallel with this, a similar programme was launched in the northeastern USA (Earll, 1880; Solemdal et al., 1984). Recent statistical analyses have shown that these programmes did not result in any long-term increase in mature cod biomass in any of the relevant fjords/local areas (Chan et al., 2003). Coincidentally, from May to October 1983, the so-called breakthrough in cod rearing happened: 75 000 cultivated juveniles were collected in a 60 000-m3 dammed pond at the IMR Austevoll Biological Station (Øiestad et al., 1985). Since then, there have been many ups and downs for gadoid mariculture in general, both in terms of available research and development (R&D) funding and for the expendable budget of the few private companies involved in the North Atlantic (Øiestad, 2005). A few positive exceptions exist such as cod juvenile production using the above-mentioned pond technique or large bags (mesocosms) (van der Meeren et al., 2005). In Newfoundland, on-growing techniques for wild-caught cod have been used periodically over the past 25 years, but have met with various problems (Brown et al., 2003). Over the last ten years, there has been increased focus on intensive gadoid production, considered to be vital to further development. Concentrated research on cod has been undertaken by Canada, Norway, and Scotland (Brown et al., 2003), inspired by already well-established protocols for sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata) (Shields, 2001; Brown et al., 2003; van der Meeren et al., 2005; Rosenlund and Skretting, 2006). Rosenlund and Skretting (2006) give an overview of current gadoid production. Both hake (Merluccius australis) and pollack (Pollachius pollachius), produced by Chile and Spain, respectively, are listed as strong candidates for future cultivation. Total world production of gadoids is expected to increase sharply in the years to come, reaching approximately 150–200 000 tonnes in 2010. The largest growth is predicted to take place in Norway. There are several reasons for initiating gadoid farming today and for strengthening ongoing efforts: (i) we are better prepared scientifically (Brown et al., 2003; Øiestad, 2005); (ii) private industry is now involved in the form of large international companies, which use closed production (life) cycles and control the entire value chain themselves, which should make them more independent and successful (Øiestad, 2005; Rosenlund and Skretting, 2006); (iii) globally, there is a steadily increasing demand for marine aquaculture products while, at the same time, the world landings of wild fish have levelled off (FAO, 2004, 2005); (iv) wild fish landings of gadoids are unpredictable per se (ICES, 2005b: 17 North Atlantic cod stocks); and (v) most wild gadoid stocks are producing far below maximum sustainable yield (ICES, 2005a, b). It should be noted, however, that cod stock status varies, ranging from collapsed (Newfoundland cod of the Grand Bank) to seriously over-exploited (North Sea cod and Baltic cod), while the status of other stocks is considered good (e.g. Icelandic cod) or satisfactory (e.g. northeast Arctic cod) (Marteinsdottir et al., 2005). Faced with dwindling stocks and fluctuating market value of farmed Atlantic salmon (Salmo salar), several countries are currently initiating large projects to expand gadoid mariculture significantly. The aim of the June 2004 symposium was to orientate international state-of-the-art science towards the development and future challenges of gadoid mariculture in the North Atlantic and elsewhere, including knowledge of environmental factors connected with fish farming. In all, 47 oral presentations and 52 posters were given within the following sessions: Quality, market, and economy of cultured gadoids. Genetics and environmental impact of gadoid culture. Health and welfare issues. Early feeding and nutrition. Early development, behaviour, and juvenile rearing. On-growth and rearing technology. Biotechnology and reproduction. The opening keynote address on the worldwide status and perspective on gadoid culture was given by Grethe Rosenlund and Magnus Skretting (Norway). Additional keynote speakers included Siri Hamnvik (Norway), Dorte Bekkevold et al. (Denmark), Ian Bricknell and Tim Bowden (UK), Kristin Hamre (Norway), Joseph Brown et al. (Canada), Ørjan Karlsen et al. (Norway), Frederick Goetz (USA), and Birgitta Norberg (Norway). The symposium revealed numerous scientific challenges to the development of sustainable and profitable farming of gadoids. One of the first questions relates to the selection of adults for breeding programmes. In the case of cod, there is some knowledge of the genetic structure of wild stocks spanning the Atlantic. In addition to different stocks residing in various large ecosystems such as the Baltic Sea, North Sea, Barents Sea, Faroe Bank, off Iceland, and Georges Bank, there also appear to be genetically distinct sub-stocks, e.g. within the Norwegian coastal cod stock. The genetic background of broodstock is important for two reasons: (i) it influences production performance in cultivation; and (ii) it plays a role in the potential genetic impact that escaped fish or fish that spawn in cages can have on surrounding wild stocks. This indicates that we need more knowledge of the genetic composition of wild stocks and the potential negative impact of farming on this composition, e.g. to find out if one needs to use local stocks as broodstock to minimize genetic impact of farming or, alternatively, to use sterile fish to prevent this potential problem altogether. Initially, the farming of cod and haddock has been based on embryos of wild broodstock. Assuming that fish are in good condition and ovaries are properly developed, eggs of apparently good quality are produced. However, in order to take advantage of the benefits of breeding programmes in the future, broodstock will be selected mainly from farmed fish. This will create some challenges in terms of broodstock nutrition and management in order to maintain high gamete quality and the health and well being of the adults. Nutrition depletion may be a problem with the repeated use of the same broodstock over several seasons. Age and previous spawning experience can also affect gamete quality in terms of egg size. A number of different techniques can be used for the spawning of gadoids, including natural spawning in large groups in closed bags, natural pair-spawning in smaller tanks, as well as manual stripping and fertilization. In the last case, the challenge is to monitor individual ovulatory rhythms to pinpoint the right time for stripping each egg batch in order to avoid the over-ripening of eggs. Also, manual stripping may result in handling stress of the broodstock that may compromise gamete quality and incur mortality. Efficient selective breeding programmes are central to improving production performance of cod and haddock, e.g. on-growth rate, feed utilization, age at sexual maturation, flesh quality, and disease resistance. Experience with other fish species such as rainbow trout (Oncorhynchus mykiss) and Atlantic salmon suggests great potential for genetic improvements of these traits. However, there are some specific challenges in selective breeding programmes for gadoids. In salmonids, eggs and sperm are stripped manually, and sibling or half-sibling groups are produced and incubated in separate units throughout the egg, alevin, first-feeding, and early juvenile growth stages up to a size of 5–10 cm when they are tagged (either by group or individually), and thereafter reared in a common environment until selection of broodstock. A similar approach has been tried on cod in Norway, but there are potential problems, both in terms of gamete quality from the manually stripped fish and large among-tank variability, particularly from first-feeding until metamorphosis. This greatly increases the amount of phenotypic variability in family appraisals, which may confound the estimates of genetic differences among the sibling groups. An alternative strategy would imply the genotyping of parents and offspring reared in a common environment. Such a strategy could be based on mating of isolated adult pairs in small tanks, collecting fertilized eggs that are either incubated in individual (per sibling group) or communal units until hatching, and thereafter, first-feeding in larger tanks together with several other sibling groups coming from the same spawning date. This latter genotyping strategy depends on a similar survival rate of different sibling groups in the communal rearing environment to maintain a large number of sibling groups. Initial studies indicate skewed survival of different sibling groups during the early-life stages as investigated by genotyping. This problem must be addressed if the strategy of a common rearing environment from first-feeding onwards is to be adopted in selective breeding programmes. We have limited knowledge of the optimal rearing environment of the early-life stages of gadoids, in particular at the time of first-feeding until metamorphosis. The physical environment (light, temperature, dissolved gases, and water turbulence and currents), chemical environment (salinity, pH, and metabolites), biotic factors (viruses, bacteria, algae, and live feed (e.g. rotifers and Artemia)), and fish stocking density result in a complex matrix of parameters that influence development, growth, feeding, swimming ability, and the general health of larvae and early juveniles. The nutritional composition of early live feeds in terms of rotifers, Artemia, and natural cold-water copepods has been studied in detail. It is still believed that feeding with naturally occurring copepods provides the highest nutritional quality. However, improved enrichment regimes for rotifers and Artemia, particularly for essential fatty acids, has led to great progress in terms of growth, normal development, and survival of juveniles. Challenges remain regarding the requirements for and the enrichment with micro-nutrients such as vitamins, minerals, and pigments. Initially, a large proportion of fish exhibited skeletal deformities in many cod hatcheries, e.g. “neck” deformities formed as a result of skewed growth and development of vertebrae. In recent years, this problem seems to have been reduced with the general improvement of rearing protocols. Still, the cause of such deformities is generally unknown. A greater awareness of the normal development of various organs, normal changes during metamorphosis, and the molecular and physiological control of these processes is essential to our understanding of how environment and early feeding interfere with fish development. This knowledge will be indispensable to identifying optimal rearing environments, feeds, and feeding regimes during the early-life stages. Another feed-related challenge is to shorten the period with live feed, particularly feeding Artemia, in intensive rearing systems. Formulated feed can be designed more easily to fit the nutritional requirements of the different early-life stages. However, technological problems remain with formulated feed, including leakage, stability of nutrients, floating/sinking properties that affect feed uptake, nutritional quality of feed, and the tank environment related to the build-up of uneaten feed and the resultant increase in bacterial load. Regarding the on-growth phase, we lack precise knowledge of both biotic and environmental requirements, e.g. optimal temperatures, light conditions, stocking densities, effects of size sorting and agonistic behaviour, specific nutritional requirements, optimal feed, and feeding regimes, as well as optimal rearing technology (tank or cage design). Optimal rearing strategies, e.g. time spent for on-growth in land-based tanks vs. time and size of transfer to sea cages for growth until harvest, will depend on ambient sea temperatures and the degree of exposure to waves and water currents at the cage site. The capacity to produce juveniles at any time of the year (based on photoperiod and temperature controlled broodstock) will enable the industry to achieve seasonal timing of a specific juvenile size. Small juveniles are expected to be insufficiently robust for transfer to sea cages with low temperatures during winter, and smaller fish are also less tolerant of high water currents and wave action. Additionally, the need for photoperiod control to delay or arrest early sexual maturation in the on-growth farms may also make it beneficial to keep the juveniles longer in land-based tanks, enabling full photoperiod control. Smaller sea cages at transfer allow easier control with feeding, survival, and disease control during the first critical months in cages. Larger and deeper cages provide better environmental conditions for large fish, particularly in vertically stratified, hydrographic environments that often provide better temperature conditions in deeper water. Atlantic cod normally grow well from the juvenile stage to a size of 1.5–2 kg. However, the onset of sexual maturation leads to a dramatic loss in body weight, typically around 30% during a spawning season. Consequently, a significant amount of time may be required to reach the desired harvest size, which may be associated with lower feed conversion, both as a result of longer production time to a given size and the losses associated with spawning. Moreover, some mortality occurs during the spawning season in cages. Therefore, one of the major challenges in the on-growth period is to delay or arrest sexual maturation. To some extent, this can be achieved with photoperiod treatment, also in sea cages, although these techniques are not fully effective as yet. Improved lighting regimes for sea cages should be developed, as well as alternative methods for puberty control such as all-female populations or sterile fish. Fish health control is a pivotal issue in farming, and a range of infections and diseases has already been identified in gadoids. Based on the experience from salmonids, more diseases are expected to develop as gadoid farming increases. The largest mortality factor for cod appears to be vibriosis, which is caused by a bacterium that normally occurs in the marine environment. Vibriosis vaccines for cod remain less efficient than those used in salmonids, although improvements are expected in both vaccination formulations and protocols. In general, nodaviruses are a threat for many marine fish species, and good sanitary and prophylactic measures should be applied to minimize the probability of infection. Gadoids are natural hosts to a large range of parasites in the marine environment. In contrast to salmonids, where freshwater to seawater transfer represents a barrier to many parasites and other infectious agents, gadoids lack such a barrier and may be more vulnerable to pathogenic parasites, bacteria, and viruses. Effective prophylactic measures are essential to avoid large disease outbreaks, starting with broodstock health screening, appropriate disinfection protocols for eggs, control of live feeds, efficient vaccines and vaccination protocols against major disease agents, and good control during the transport of live material between different sites and regions. A major improvement in salmon farming was the separation of different year classes at different sea cage sites to avoid horizontal transfer of diseases between the year classes in the on-growing farms. Similar approaches should be adopted for gadoid farming in sea cages. A health problem specific to gadoids is connected to the rather late development of immune responses to vaccines in the life cycle combined with early exposure to a range of potential pathogenic agents. Cod larvae cannot be vaccinated before first-feeding, at a time when introduction of live feed also introduces potential pathogenic agents. A possible strategy for early protection of cod larvae and juveniles is to use probiotic bacteria, e.g. non-pathogenic bacteria that may prevent the growth of pathogenic bacteria in both the environment and on the cod themselves. Flesh quality is central to achieving acceptance and a suitable price for the farmed gadoids in the market. Farmed cod have been well-received by many chefs and in farmed fish to have a negative that farmed cod better with when they are that they are farmed In farmed cod as well as wild in some recent the quality of farmed fish will not be to wild fish, but this is not a Farmed gadoids may have to be as a specific separate from wild The of could also be essential to the of farming, e.g. use of and the yield in farmed cod is than in wild cod, other body a large biomass and could provide The can be to further such as of In the future, farmed cod will be mainly in the fish market. However, on production and it is that farmed gadoids will to a larger market, one typically associated with of wild cod and A dramatic increase in gadoid farming a of issues. One major issue is sustainable feed of and fish are and are for fish farming in general and for gadoid farming in may marine or other marine knowledge of to such alternative feed in terms of production fish and quality, is and this and health issues. The environmental impact of gadoid culture must also be addressed and including such as and and of diseases and genetic impact of and spawning in cages on wild and Fish welfare must also be e.g. by understanding the requirements throughout the life cycle and improving rearing environments and to prevent production and infectious research are to these in better detail. The ongoing programme in Norway, as well as other such as The Atlantic Cod and Development by will produce a range of molecular such as which allow approaches in the of the effects on of and physiological studies will greatly our understanding of the environmental requirements and impact of throughout the life nutritional requirements and impact of alternative feeds, and the immune and in the development of Moreover, approaches as well as other techniques can to the production of sterile fish, fish with better flesh quality, and allow for alternative use of The symposium scientific since the in in 1983, and the science is in the that were addressed at the Gadoid progress has been in the areas of broodstock juvenile production, feed disease and on-growth technology. A further of gadoid farming is as a of breeding of rearing protocols and feeds, as well as better knowledge of harvest quality and market. Development of rearing technology will allow the development of areas for gadoid farming. The symposium role as a place for and other in gadoid and the that were in the development of gadoid farming the need for a symposium within a few Also, the for mariculture of hake and pollack indicates that gadoid farming can the countries the North Atlantic. The expected increase in demand for fish for will successful and management of wild stocks with successful development of marine aquaculture of gadoids.

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