Sustainable Tuna Aquaculture – New Horizons

The SELFDOTT project has complied amply with the proposed objectives, substantiating the results of reproduction of Atlantic bluefin tuna in captivity obtained in the previous project REPRODOTT and laying down the bases for the production of fingerlings of this species and for the development of more efficient feeds respectful of the environment. Even if the advances achieved in the project can be classified as spectacular, there are still many aspects that must be improved, and, therefore, it is concluded that the large-scale commercial production of this species in a profitable manner is not yet developed sufficiently enough to fuel a new aquaculture industry.7 FP European Commissio

Spontaneous spawning of Atlantic bluefin tuna Thunnus thynnus kept in captivity

Beginning 48-72 h after GnRHa treatment in 2009, massive spawning occurred for 17 days, with a daily maximum of 34 million eggs collected (SELFDOTT, 2010). On 17th June 2010 spontaneous spawning started in cage R2. From this day onwards and more or less daily viable eggs were obtained from both cages so no hormonal implants were used. Fish spawned intermittently for a period of 34 days in both cages, with a total of 58 million eggs collected. Cage R1 spawned for 26 days and produced 48 million eggs and cage R2 spawned for 28 days and produced 10 million eggs (Figure 1). As happened in 2009 (SELFDOTT, 2010), due to the almost non-existence of currents throughout the spawning period, almost all the eggs were collected at the surface, held by the plastic curtain. Only a small amount of eggs were captured by the egg collectors, which were designed to operate under current. Eggs were transported to the IEO facilities in Mazarrón (SE- Spain) where they were incubated. On average, the hatching rate was above 90%. No difference in hatching success was observed between 2009 (from hormonally treated cage) and 2010 (from spontaneously spawning fish).Commission of the European Communities, specific RTD program of Framework Program 7, SELFDOTT, “From capture based to self-sustained aquaculture and domestication of bluefin tuna, Thunnus thynnus” (GA 212797)

Gamete biology: Perspectives for Bluefin Tuna Aquaculture

Taking care of fish reproductive physiology and gamete biology allowed significant progresses in fry production control for many commercially interesting fish. Can it be a similar situation for bluefin tuna? Fish gamete production results from long processes controlled mainly by climatic conditions, mediated by neuroendocrine and endocrine factors. The possibility to monitor the development of germinal cells by successive sampling in individual fish which easily breed in captivity, has allowed learning about the sequences of gametogenesis and their control, as well as important characteristics of fish gamete biology. The female ovarian cycle involves a progressive accumulation of yolk in the oocytes (i.e., vitellogenesis), followed by cytoplasmic and nuclear events related to maturation and ovulation. The phases of vitellogenesis and maturation are of different duration in different species. In captive fish the endocrine regulation of reproduction may be disrupted by stress, thus preventing spontaneous spawning, while the application of exogenous hormones at the conclusion of gametogenesis allowed production of good quality gametes. In males, gamete production is not continuous as in mammals. Spermatozoa are produced after a cycle that includes a resting period, followed by continuous or discontinuous sequences of spermatogenesis (spermatogenesis sensu stricto, spermiogenesis and spermiation). The discontinuity of fish sperm production may induce a phenomenon of ageing along the period of spermiation, which decreases the quality of semen with time. Wild bluefin tuna breed in specific areas during a short summer spawning season. When kept in cages in the area of Cartagena (Spain), they present developed gamete stages at the same time as wild fish, but, until now, neither mating behavior nor eggs have been observed as was the case in Japan. It has not been possible to monitor individual gonad recrudescence by successive sampling, due to inability to handle the fish without causing mortality, so that the reproduction failure remains unexplained. Hormonal stimulation may be an interesting alternative but its use requires an assessment of gonadal stage to be performed properly. The high post-handling mortality of bluefin tuna in captivity is a real bottleneck for reproduction control. The improvement of handling and the use of less stress-susceptible individuals may be a major progress for bluefin tuna reproduction control. The occurrence of a second generation of juveniles in Japan, subjected to first domestication selection may provide very interesting experimental fish.EU 5FP REPRODOTT (Q5RS-2002-01355

The key neuroendocrine regulators of the onset of puberty in the Atlantic bluefin tuna (Thunnus thynnus)

Recently, significant progress on spawning induction in captive bluefin tuna (BFT, Thunnus thynnus), has been achieved providing the basis for the species' domestication. To further promote the development of a self- sustained BFT aquaculture, we investigated first sexual maturity in BFT reared from an immature stage in captivity. Accordingly, our major objectives were to evaluate: (i) maturational status of the brain-pituitary-gonadal (BPG) axis, and (ii) responsiveness of the BPG to exogenous hormones. Special emphasis was given to characterize the gonadotropins follicle stimulating hormone (FSH) and luteinizing hormone (LH) that act as central regulators of gonadal development and gamete maturation. The growth parameters recorded for the captive BFT juveniles are consistent with the length-weight relationship established for wild Mediterranean BFT stocks. The histological analyses of the gonads indicate advanced sexual maturation in BFT males compared to females, yet it is not yet clear whether this phenomenon typifies wild stocks or is induced due to the culture conditions. The hormone measurements show expression and accumulation of both gonadotropins in the pituitaries of immature and mature BFT. The pituitary LH content increased concomitantly with the age of the fish, exhibiting sex dimorphic patterns (i.e. 3-fold higher levels in females) in adult but not in juvenile BFT. The pituitary FSH levels, however, were elevated in 2Y immature males and in fully mature adults. Comparable to mammals, the intra-pituitary FSH/LH ratio was found to be higher (>1) in sexually immature than in maturing or pubertal BFT. Nevertheless, in the 3Y BFT females, which were all immature, the onset of puberty appears to require some other prerequisites, such as a rise in the LH storage above a minimal threshold. Our in vitro trials further demonstrated the capacity of rFSH and to a lesser extent that of rLH to stimulate cell proliferation in the immature ovarian and testicular fragments. Both rFSH and rLH have failed to stimulate steroidogenesis, yet pre-treatment with KiSS containing EVAc implants appeared to potentiate FSH-stimulated steroidogenesis in the immature testes. On the other hand, the expression levels of both the GtH-R and IGF I genes in the testicular fragments, derived from BFT juveniles and further exposed to the rLH treatment, showed dose-dependent pattern. Future studies testing the effects of captivity and hormone-based treatments on precocious maturity at relatively small body size are expected to facilitate the handling in confined environments, and to greatly improve the cost-efficiency of BFT farming.Postprin

Effects of in vivo treatment with the dopamine antagonist pimozide and gonadotropin-releasing hormone agonist (GnRHa) on the reproductive axis of Senegalese sole (Solea senegalensis)

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Reproducción del atún rojo Thunnus thynnus en jaulas flotantes obtención de puestas masivas mediante implantes hormonales

In the frame of the SELFDOTT project (From capture based to SELF-sustained aquaculture and Domestication Of bluefin tuna, Thunnus thynnus) captive-reared Atlantic bluefin tuna (Thunnus thynnus) (n=15, estimated body weight=90 Kg) maintained for 3 years in captivity in El Gorguel (Cartagena, Spain) were administered a gonadotrophin releasing hormone agonist (GnRHa) implant underwater, during the natural spawning period for this species in the Mediterranean Sea (June). Beginning 48-72 h later, massive spawnings occurred everyday for 17 days, with a daily maximum fecundity of 34 million eggs. Egg collection was accomplished by placing a special curtain around the perimeter of the cage and at 6 m allowed the floating eggs to be maintained within the cage and be collected at night and sunrise with 500 ìm mesh size nets from the surface of the water.Proyecto SELFDOTT. UE

Advances in greater amberjack (Seriola dumerili) research: the DIVERSIFY project

The greater amberjack (Seriola dumerili) is a species with high potential for the EU aquaculture due to its fast growth (6 kg in 2.5 years), excellent flesh quality and global market. Its farming in the Mediterranean region started in the 1990s with wild-caught juveniles, but the production is still negligible, as several bottlenecks exist for its industrial production. These include the absence of reliable reproduction, limited availability of juveniles, lack of knowledge on the nutrient requirements and pathology of the species. The EU FP7-funded DIVERSIFY project (www.diversifyfish.eu) examines the major aspects of greater amberjack aquaculture in order to overcome these bottlenecks and develop appropriate rearing methods for commercial production. This article provides some highlights from the first 2 years of the project.Postprin

Obtención de puestas masivas de huevos de atún rojo (Thunnus thynnus) en cautividad, durante 3 años consecutivos

Within the framework of the SELFDOTT project, captive-reared bluefin tuna (Thunnus thynnus) maintained in captivity since 2007 in Cartagena (Spain) produced massive spawning during the natural period for this species in the Mediterranean Sea (June-July). The fish were induced with GnRHa implants in 2008 and 2009. In 2008 no spawnings were detected. From 2009, massive spawnings occurred being spontaneous (without hormone implants) in 2010 and 2011. The total egg collection was 140 million in 2009, 60 million in 2010 and 160 million in 2011.7º Programa Marco de la Unión Europea, “Food, Agriculture, Fisheries and Biotechnology" del Proyecto SELFDOTT (From capture based to SELF-sustained aquaculture and Domestication Of bluefin tuna, Thunnus thynnus)” GA 212797