WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2023 29 can lead to eutrophication of the local environment, and lower incubation temperatures slow down development and increase production times. Inconsistent sea-water growth of triploids is often attributed to the idea that they have a lower temperature optimum and lower hypoxia tolerance than diploids. Temperatures and oxygen levels fluctuate in sea-cages, quite often outside the optimum for growth, and it was thought that this was more problematic for triploids than diploids. Small-scale tank trials would suggest this is true, with triploids showing signs of reduced performance compared to diploids when kept in seawater at 15°C or higher (Sambraus et al. 2018). This is below the maximum values in southern Norway where summer seawater temperatures can be around 20° C (Madaro et al. 2021). The Challenges of Scaling Up The initial farm trials in Norway began in 2007 through an EU project coordinated by the University of Stirling in Scotland (Table 1). The partners in Norway were the Institute of Marine Research (IMR) and two commercial entities, Marine Harvest AS (now Mowi AS) and AquaGen AS. Early results were promising, suggesting triploid growth could be equal to that of diploids. A semi-commercial trial followed at the IMR Matre research station (mid-Norway) in 2009 indicating triploids grew better in freshwater, but poorer at sea (Fraser et al. 2013). They also suffered from higher mortalities and more downgrading at slaughter than diploids. In particular, triploids had more “loser” fish, which have stunted growth and poor condition (Figure 3C), and more skeletal deformities. In hindsight, the bone deformities could be expected as the triploids in this trial had been fed a standard diploid diet throughout, which would not have met their dietary phosphorus demands. By the mid 2010’s, the advice was that triploids should be fed specialized diets to prevent problems with bone deformities and cataracts, and they should be farmed in northern Norway where conditions are colder (below 15° C in the summer, Madaro et al. 2021) compared to southern Norway. Between 2014 and 2019, 54 groups of triploids, in total around 16 million fish, were transferred to commercial seacages in northern Norway. The reports are all publicly available (Stien et al. 2019, 2021a, b). The trials were performed under the issuing of “green licenses” in collaboration with Marin Helse AS, Norway Royal Salmon Farming AS, Nor Seafood AS, and Wilsgård Fish Farming AS in the Troms and Finnmark regions of Norway. Triploidized eggs were produced by two commercial suppliers, AquaGen AS and Stofnfiskur AS, now Benchmark Genetics Iceland. The IMR participated in the documentation of their performance. Among other requirements, the green license required the use of smolts over 100g, cages with skirts (which shield fish from lice but at the cost of reduced water flow and oxygen concentrations), cleaner fish to reduce sea louse infections, and the use of “escape proof” nets and sterile fish. The trials were aimed at establishing whether triploid performance was acceptable. Poor egg survival and low triploidization success hampered early efforts but improved over time. Triploidization success was as low as 44 percent in one batch from 2014, but by 2019 only one batch had a success rate below 100 percent, and it was 98 percent. However, farmers have had less success at sea. Triploids generally suffered more from winter sores, especially in fish put to sea in the autumn compared to spring, and with infection by the gill parasite Parvicapsula. In 2022, it was also reported that triploids were more susceptible to infectious salmon anemia (ISA) than diploids, with the authors concluding triploids should be banned or produced in bio-secure locations (Aunsmo et al. 2022). Infectious salmon anemia is a viral infection, which caused a major loss of production in Chile beginning in 2007. As a result of the 2014-present trials, the FIGURE 3. Welfare issues in triploid salmon. (A) Vertebral deformities are more frequently found in triploids at harvest. (B) Ocular cataract (cloudy eye) in a smolt. (C) “Loser” fish more frequently found in triploids at harvesting. The fish at the top is not a loser and is the same age and from the same sea-cage. (CONTINUED ON PAGE 30)
RkJQdWJsaXNoZXIy MjExNDY=