All that Atlantic sturgeon fry need are plenty of food, space and clean tanks! JERRE W. MOHLER1 There are common practices that can be applied to sturgeon culture regardless of which species is being reared. Some examples are: 1) use of spawning hormones to induce sperm expression and egg ovulation, 2) egg fertilization techniques and, 3) preparation of fertilized eggs for incubation. Also, events are fairly predictable in the development of a sturgeon embryo as it proceeds fairly rapidly from a 2 mm-diameter ball of cells to a tadpole-like fry. However, once Atlantic sturgeon fry are fully hatched out and begin to deplete the yolk sac the one-size-fits-all approach to sturgeon culture may have to be refined, especially at first-feeding. As in most early life stage fish culture situations, the crucial period when most mortality can occur is during the conversion from yolk sac nutrition to introduced feed. At that point, not only is it important to have an acceptable type of introduced feed, but the timing of its introduction and the quantity made available to the fry are also vitally important. Larvae of the Siberian sturgeon (Acipenser baeri), Russian sturgeon (A. guldenstaedti), sterlet sturgeon (A. ruthenus), and white sturgeon (A. transmontanus) were successfully weaned to compound diets (Williot et al. 2001) but only the Atlantic sturgeon ( A. oxyrinchus), the subject the discussion here, has been successfully started on live feed (brine shrimp). With support from our state partners and other stakeholders, we performed numerous experiments with first-feeding Atlantic sturgeon fry at the U.S. Fish & Wildlife Service's Northeast Fishery Center in Lamar, Pennsylvania (NEFC) from 1993-1998. These experiments were initiated in response to the decline of Atlantic sturgeon wild stocks as a result of past overharvesting for caviar and meat as well as habitat alterations, all of which were injurious to wild populations. During this six year period of experimentation, fry were produced using sperm and eggs obtained from wild caught Hudson River broodstock, inasmuch as no mature domestic stocks yet existed. From these experiments came strategies that were effective at producing good survival and growth of firstfeeding Atlantic sturgeon and subadults up to 12 years of age. All of the knowledge obtained from these practical experiments has been documented in the Culture Manual for the Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus (Mohler 2004). However, opportunities to produce young Atlantic sturgeon in our hatchery have been limited to only 11 attempts overall, because of the difficulty of obtaining ripe females in the wild. We often caught over 100 mature males on the spawning grounds while only capturing one or two females. Compared with the hundreds of potentially-spawning fish available each year in a typical trout hatchery, occasions to fine tune early culture of Atlantic sturgeon have been few. Nonetheless, we found that given good quality eggs along with enough rearing space and other resources, it is possible to achieve an 80 percent hatch rate for the eggs and a nearly 75 percent subsequent survivai of fish to the fingerling stage. If gravid females are available and proper spawning and egg fertilization procedures have been followed, a hatch of larvae can be expected in about 60 hours after fertilization when incubated at 21 °C. Those conditions were proved successful for Hudson River stock, but those stocks in more southern or northern latitudes may have somewhat different optimum egg incubation temperatures and times. When larvae began to hatch and flow from the incubation jar into the culture tank, the water temperature was slowly reduced, over 24 hours, to l 7°C and. a countdown to the next important milestone, benthic clumping behavior, began. That stage was reached in about four days and was quite evident when larvae began to crowd together on the bottom of the culture tank and form curiouslooking patterns, which, at times, resembled a single organism rather than numerous individuals clumped together (Figure 1). This behavior lasted about 4 days, then larvae dispersed more evenly throughout the tank in preparation for finding food because by that time, their yolk sac (Figure 2) was nearly depleted. Our experimentation with tank culture showed that offering live WORLD AQUACULTURE 55
RkJQdWJsaXNoZXIy MjExNDY=