WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2016 33 white seabass Atractoscion nobilis, locally known as cabicucho. Despite official protection (side bar 1), illegal fishing for totoaba continues. The pessimistic view is that the species will move closer to extinction, like the bahaba did in China. An alternative, more optimistic view is that there is still time to save the totoaba. However, this can only be accomplished with a comprehensive effort that includes effective enforcement of regulations, restoration of habitats, and a fisheries enhancement program to help make up for the loss of recruitment. In any case, aquaculture is essential for preservation of the species. Totoaba Aquaculture The development of totoaba as an aquaculture species was facilitated by the existing body of knowledge about two closelyrelated fish: the red drum Sciaenops ocellatus, probably the most studied sciaenid, grown for food in the Gulf of Mexico and elsewhere, and the white seabass Atratoscion nobilis, reared in California for restocking natural waters. Totoaba aquaculture owes much to the pioneering program created 20 years ago by the Government of Mexico at the Universidad Autónoma de Baja California (UABC) in Ensenada. Procedures for broodstock capture, maturation, larval rearing, and juvenile grow-out were initially developed at UABC (True et al. 2009, True 2012). This was followed several years ago with the addition of a second program at the Center for Reproduction of Marine Species of the State of Sonora (CREMES) in Bahia Kino. Both institutions have released thousands of juveniles into the wild as part of conservation efforts and have contributed to the emerging farming of totoaba by supplying fingerlings to startup aquaculture operations. Between 2007 and 2010, two private companies started smallscale trials to grow totoaba fingerlings produced at UABC in ponds near Ensenada. Despite the many challenges associated with doing something for the first time and of the low winter temperatures in the area, the fish grew to an average of 1.5 kg in 16 months. The results were encouraging, but not enough to generate investment. In 2012, Pacifico Aquaculture stocked juvenile totoaba from the hatchery at UABC in surface cages in the ocean near Ensenada. The trials were moderately successful but again the low temperatures allowed only limited growth. In 2013 a new player entered the totoaba arena. Earth Ocean Farms (EOF) stocked juvenile totoaba from UABC in cages in the Sea of Cortez near La Paz. By moving the fish from their northern spawning and nursery grounds to a southern location, more characteristic of the species’ feeding and overwintering areas, EOF was able to take advantage of the growth potential of the species, renewing interest in commercial and conservationminded aquaculture. The remainder of this section describes these experiences, with which the authors are associated. The totoaba hatchery at EOF (Fig. 5) consists of broodstock husbandry, spawning, and larval culture sections, culminating with the production of fingerlings. Each of these steps has specific systems and protocols that must be operated with great care to achieve success. Because of their size, totoaba broodstock require large circular tanks (Fig. 6). To supply excellent water quality and to prevent potential pathogens, broodstock must be maintained in systems that provide adequate filtration and disinfection of the incoming water. This is achieved with recirculating aquaculture systems that recycle more than 90 percent of the system volume daily through particle and biological filters and ultraviolet sterilizers. By utilizing recirculating technologies, less “new” water is needed, improving biosecurity and water quality. Another critical factor associated with broodstock husbandry is the use of high-quality natural and prepared feeds to supply the complex mix of nutrients required for healthy broodstock maturation and egg production. As is the case with many fish species, the main environmental cues associated with egg production and spawning of totoaba are temperature and light. By matching the natural temperature and sunlight patterns encountered throughout their annual migrations EOF developed photothermal protocols to promote gonadal maturation and spawning in the hatchery. These procedures are continuously optimized based on egg production success, a process that can take years to refine. In the interim, hormone injections are used to induce the final stages of maturation and spawning. (CONTINUED ON PAGE 34) Restocking programs and genetic considerations The long-term effects of hatchery-reared fish on the fitness of wild populations are an important concern in the design and management of stock enhancement programs. Proper management is essential to maintain genetic diversity, prevent genetic contamination, and avoid genetic drift of wild populations. Diversity maximizes the potential for adaptation and survival. Improperly done, stocking of hatchery juveniles can be harmful to wild stocks. For restocking, hatchery practices should maximize genetic diversity by assembling founder populations from locations as diverse as possible, and by partially replenishing broodstock from the wild at regular intervals. Captive fish populations tend to loose genetic diversity due to their small size and to the large contribution of a few individuals to the next generation. Coupled with the high fecundity of marine fish, this can result in large numbers of offspring from very few parents, creating serious inbreeding depression in just a few generations. This problem can be prevented by using appropriate breeding schemes and by limiting the numbers of juveniles from the same spawn that are released into the wild. Captive populations may also loose fitness due to intentional or unintentional domestication to the culture environment. Fish produced in hatcheries for aquaculture purposes are often selected for optimum culture characteristics, which include adaption to the culture conditions and selection for commercially desirable traits, such as fast growth, efficient feed conversion, and resistance to diseases. Hatcheries that produce juveniles for restocking programs and for commercial farming need to utilize two very distinct breeding schemes; one that maximizes the genetic diversity for restocking and one that domesticates the species for optimum performance under culture conditions.
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