56 JUNE 2014 • WORLD AQUACULTURE • WWW.WAS.ORG above 1 kg had gonadosomatic indices between 5 and 10 percent (Fig. 2). Eggs obtained by catheter were in developmental stages close to ovulation between the end of May and the middle of June. With HCG treatment, females spawned when they were stocked with a ripe male in 300-L mating tanks at 19 °C about 24 h to 48 h after hormone administration. On average, 70 g of eggs per kg female were spawned; eggs were between 0.9 and 1.0 mm diameter after hardening. Eggs were only slightly sticky and almost neutrally buoyant. Strip spawning was an easy way to obtain unfertilized eggs (Fig. 3). In 4 of 13 spawned batches, hatching rate of larvae was very low, ranging from below 0.1 percent to 0.4 percent (Table 2). At 20 °C, hatching occurred 40 h after spawning. Larval length was approximately 3 mm. All examined larvae were free of visible deformations. Four days after hatching, HSB larvae started feeding. Small Artemia nauplii could be ingested seven days after hatching. In outdoor tanks, spawning behavior and natural spawning was also monitored in females that were not hormonally treated. Egg release occurred near the surface as individual females were driven and followed by a group of males. In the days following spawning, hatched larvae could be collected from tanks. These observations provide evidence that HSB can reproduce in the climatic conditions of Germany. Similar results, with some hatching and developing larvae from a few HSB matings, were also obtained in another recently published German study (Lehmann et al. 2012). Although the fitness of HSB larvae in natural environmental conditions has not yet been identified, the results of this study demonstrate a certain risk for invasive behavior of escaped HSB in Germany. The marginal survival rates observed among HSB offspring in natural and controlled spawns represent a worstcase scenario. On the one hand, reproduction performance is much too low for economic fingerling production and independence from expensive post-larvae imports. On the other hand, responsible farmers should not stock HSB in net cages, ponds or tanks without constructed barriers to open waters, to protect these from potential invasions by a top predator species. Conclusions • Hybrid striped bass showed good growth performance in RAS and outdoor ponds in the climatic conditions of northern Germany, • The product quality of HSB for the German seafood market was promising, • Sub-adult and adult HSB could survive winters in northern Germany under ice, • HSB can spawn naturally and invasive behavior cannot be excluded, • Marginal hatching and survival rates of HSB fry otherwise impede farmers own commercial fingerling production, • For ecological reasons, HSB is not acceptable as an alternative candidate in German farm sites without constructed barriers to open waters. Despite promising growth performance, product quality and medium- to long-term marketing opportunities, by reason of strict environmental legislation and distinct ecological awareness, hybrid striped bass will not gain importance as an alternative candidate in German aquaculture. Notes Andreas Müller-Belecke* and Christa Thürmer, Institute of Inland Fisheries, Potsdam-Sacrow, Im Königswald 2, D-14469 Potsdam, Germany. Web page: www.ifb-potsdam.de/; *corresponding author: E-mail: andreas.mueller-belecke@ifbpotsdam.de; Fax: +493320140640. Marcel Böhm, Desietra GmbH, Kruppstraße 5, D-36041 Fulda, Germany. Web page: www.desietra.de References Baer, J. 2004. Eignung von Zander und Streifenbarsch für Kreislaufanlagen. Fischer & Teichwirt 55:606-608. Gottschalk, T., G. Füllner and M. Pfeifer. 2005. Möglichkeiten der Einführung neuer Fischarten als Objekte der Aquakultur in Sachsen. Aufzucht von Hybrid-Streifenbarschen in einer „In-TeichKreislaufanlage“. Schriftenreihe Sächsische Landesanstalt für Landwirtschaft 14:1-53. LEFT, FIGURE 3. Artificial stripping of a HSB female one day after HCG injection. RIGHT, FIGURE 4. Hybrid striped bass.
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