Search

Inland fisheries contribute substantially to the economies of England and Wales. Many trout fisheries rely partly or entirely on stocking to maintain catches. Given that farmed trout often differ genetically from their wild counterparts, wild trout could be at risk of reduced fitness due to interbreeding or competition with farmed fish. As a preventative measure, the UK Environment Agency has implemented the “National Trout and Grayling Strategy” which will only give consent to the stocking of rivers and some still waters with sterile, all-female triploid brown trout. In order to produce an optimised hydrostatic pressure induction protocol three experiments were conducted to (1) determine the optimal timing of application post-fertilisation, (2) define optimal pressure intensity and duration of the shock and (3) study the effect of temperature (6–12 °C) on triploid yield. Triploid rate was assessed using two different ploidy verification methods (blood smear and flow cytometry). Results indicated high survival to yolk sac absorption stage (69.2–93.6%) and high triploid yields (82.5–100%) from the range of treatments applied. Furthermore, no significant differences in triploid rates were shown when shock timings and durations were adjusted according to the temperature used. In all treatments deformity prevalence remained low (

article i nfo Article history: Keywords: Triploid Out-of-season Smoltification Photoperiod ATPase Atlantic salmon Production of sterile triploid Atlantic salmon (Salmo salar) would appear to be the best strategy to address the growing concerns on environmental impacts of escapees. However, the industry relies on a year round supply of smolts to ensure continual production and to date the production of out-of-season (S0+) triploid smolts has not been reported. The present study demonstrates that S0+ triploid smolts can be produced using an accelerated "square-wave" photoperiod (LL-LD 9.5:14.5-LL) under ambient water temperature. Such a regime advanced the timing of smoltification by 3 months (S0+) relative to their siblings under an ambient photoperiod (S1+) as observed through body silvering, fin darkening, decrease in condition and significantly increased gill Na + ,K + -ATPase activity. Importantly, triploid S0+ fish smolted 4 weeks earlier than their diploid siblings. In S1+ populations, no difference in smolt time was observed although triploid fish also achieved a higher weight. Furthermore, deformity prevalence was very low during the fresh (≤5%) and seawater (≤2.5%) stages within both ploidies mainly represented by spinal deformity and operculum shortening. Family effects for growth and condition were clear, however, no significant family/ploidy interactions were observed although this was based on only two full-sib crosses. These results are promising but there is still a long way to go before triploid can become a commercial reality. Further studies are required to optimize and refine husbandry protocols, define breeding strategies especially regarding family selection and overall better understand triploid salmon physiology.

The production of sterile triploid Atlantic salmon (Salmo salar) may help address the increasing pressure on the industry to reduce potential breeding between farmed escapees and wild fish populations. However, many previous studies have observed poor performance at sea in triploid stocks (growth, survival, and deformity). This may result from poor early hatchery performance and a strong parental effect. Therefore, in the present study, two year classes (2007 and 2008) of mixed sex fish were created (10 males:10 females) to examine ploidy interactions on hatchery performance. Egg batches were divided in two at fertilisation with one group subjected to a hydrostatic pressure shock to induce triploidy. Triploid rate was confirmed at 100% in all groups, verified by red blood cell nucleus length measurements. Survival to hatch did not differ between ploidy. However, reduced survival was found to strongly correlate with gamete quality. During the hatchery phase ploidy significantly affected size at hatch, with diploids generally larger than triploids. Growth advantage of diploids over triploids was only maintained for 6 weeks post-first feeding, with triploids generally out-growing their diploid siblings by the end of the hatchery phase. Deformity prevalence in first feeding stages was generally low (mean