WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2014 55 (CONTINUED ON PAGE 56) RAS sector continues to search for candidate fish species that provide sufficient earnings to justify the high production costs associated with these systems. By virtue of its outstanding product quality, good growth performance and tolerance to low temperatures, the hybrid striped bass (HSB) became a fish of interest to the German carp and RAS sector. Some years ago, the growth performance, FCR and survival rates of HSB in RAS, traditional carp ponds and other outdoor sites was evaluated, with consideration of the climatic conditions of northern and central Germany (Wedekind 2001, Wedekind and Wolf 2004, Baer 2004, Gottschalk et al. 2005, Pfeiffer et al. 2006, MüllerBelecke and Zienert 2006). In keeping HSB in net cages, ponds or tanks without constructed barriers to open waters, unwanted escapes into nature is likely. Scant information about the reproductive potential of HSB is available, making assessment of the risk of invasive behaviour difficult. Therefore, the goal of this study was to summarize the performance of HSB grown in German rearing conditions and to obtain further information about the reproductive and outdoor overwintering potential of HSB in the climatic conditions of Germany. Growth Performance of Hybrid Striped Bass Hybrid striped bass postlarvae of different age groups were imported from Israel, weaned to artificial diets and grown in RAS at 22-24 °C. Specific growth rate (SGR), feed conversion ratio (FCR) and survival were determined for different age classes and stocking densities in RAS and different outdoor systems. At rearing temperatures between 22 and 24 °C, 700-g fish were obtained from postlarvae within 13 month in RAS. Losses were marginal when individual body weight was greater than 10 g. The FCR ranged between 1.1 at a body weight around 40 g and 1.5 at a body weight greater than 500 g (Table 1). The performance of HSB in RAS was acceptable, but was exceeded by pike perch Sander lucioperca, another recently tested and, in Germany, highly acclaimed and high priced percid species (Zienert and Heidrich 2005). The growth performance of HSB reared in carp ponds in the climatic conditions of northern Germany using manufactured feed was promising (Gottschalk et al. 2005, Pfeiffer et al. 2006). Three growth periods, from April to October, were needed to obtain 800-g HSB from postlarvae. The FCR was 1.3 in the second summer and 1.5 in the third summer. Specific growth rates decreased from 1.0 to 0.6 percent. Quality Parameters Physical and chemical carcass quality parameters were determined for HSB or pike perch fillets (fried, unseasoned). There were distinct differences in fat content, with about 11 percent in the fillet of HSB and only 2 percent in pike perch fillets. In sensory comparisons, preferences for HSB or pike perch fillets with regard to odor, color, texture and taste were compared (24 pairwise comparisons according to DIN 10 954:1997-10). Fillets of both species were appreciated as premium quality fish products. The test panel sensed a much more pronounced odor, texture and taste in HSB. Quality parameters indicated a promising potential of HSB for the German seafood marked. However, it is difficult to sell the product in Germany, inasmuch as prices for imported seed and production costs for manufactured feed in RAS and outdoor systems were greater and the product is not yet known and accepted by consumers. Reproductive Capability and Outdoor Survival To evaluate overwintering potential and reproductive capability, groups of HSB were transferred to static, aerated outdoor tanks (20 m³) at a mean body weight of about 300 g. HSB were maintained at stocking densities between 0.5 and 1.5 kg/m³, outdoors for 2 to 3 years. Artificial diets were provided in restricted rations. Environmental parameters were monitored and fish were checked for their ability to survive winter conditions. If fish were well-conditioned and not stressed, rearing water temperatures of around 4° C were tolerated for one month, to some extent under ice, with negligible mortalities (Fig. 1). In spring, gonadal development of the fish was followed closely. To induce ovulation, one group of maturing females was treated with human chorionic gonadotropin (HCG) (500 I.U. per kg of female body weight). Another group of adult HSB were monitored for natural spawning activity and reproductive success. The onset of gonadal maturation could be detected in fish of about 500 g in April. When water temperatures reached 15 to 20° C in May/June, most male HSB with motile spermatocytes could be stripped. Sperm motility averaged 4:15 min. The mean percentage of motile spermatozytes was about 60 percent. The majority of females TOP, FIGURE 1. Water temperature profiles in tanks during wintering HSB outdoors. BOTTOM, FIGURE 2. Ovary of a HSB female in June.
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