Domesticating Striped Bass Broodstock
By Merrill Leffler
Striped bass aquaculture, while growing, is still only a tiny portion of the U.S. seafood economy. Limiting that growth is an inability to spawn the fish year round as is done with other more valuable aquaculture species. The fact that growers must depend on collecting fish from the wild restricts the amount of fish they can spawn. What we need, says Reginal Harrell, a scientist at the University of Maryland Center for Environmental Science, is "domesticated, not captive broodstock." He has focused his research career on the culture and genetics of striped bass and its hybrids. In a current project, he and John Jacobs have been comparing the growth characteristics of striped bass juveniles from five different regions of the east coast in order to determine if some strains reach harvest size substantially faster than others.
While their findings will be of interest to growers, there are limitations, he says, to just how applicable the results are - that is because Harrell has to evaluate the offspring of broodstock captured in the wild. There is no baseline to the broodstock stripers from Florida, South Carolina, Maryland and Canada - they all came to maturity under different conditions in their regions. Different temperatures, different salinities, different nutrition. In other words, says Harrell, we don't know whether our results of juvenile growth to harvest size were the result of inherent differences in those strains or if they were due to the environmental conditions the fish experienced before we captured and spawned them.
The only way to derive conclusive comparisons would be to have broodstock fish that were first reared, then bred in the hatchery. But domesticated striped bass broodstock have been very slowly coming - that means rearing juvenile striped bass to maturity, perhaps four to six years or so, then spawning them; that second generation is then raised to maturity, then spawned, and so on. The ability to do this has been nearly impossible (see "Spawning Stripers on Demand"). And yet, without such domesticated broodstock, it is next to impossible to compare different strains, let alone breed fish for different traits, as agriculturalists have bred animals for centuries.
Over the last 15 years, though, University of Maryland researcher Curry Woods has quietly been doing just that: breeding striped bass at the Crane Aquaculture Facility. And he has begun to have success - small, but significant success, says Harrell - that holds exciting promise for the future farming of striped bass and its hybrids.
"Some of Curry's work," says Jim Carlberg, president of Kent Sea Farms in San Diego, one of the nation's largest striped bass producers, "is the only such work of its kind in the world."
Breeding Selective Stock
"We have been slowly developing a domestic population of pure striped bass," says Woods - "we're now into the fourth filial generation removed from the wild." This is a domestic population, he points out, rather than an acclimated captive one. "It's a distinction" he says "that's not often made."
Woods's operation at Crane, in Baltimore City, has produced the first selectively bred stocks, namely superior males and superior females. "We have a database on each fish. We know what we have to choose from," he says, with regard to growth. In a recent field trial, he compared the progeny produced by third generation striped bass with a first generation sunshine bass (a hybrid cross between a white bass female and striper male). "Our fish are growing 40 percent faster," he says.
With domesticated broodstock whose characteristics are known, growers can selectively breed for those characteristics, whether they are faster growth, better disease resistance, or higher feed conversion efficiency. "We already have examples of how you can breed for growth," Woods says. "It took us six years to get the first females to produce; we've gotten third generation stripers to reach maturity in three years."
"We're still in a research phase," Woods is quick to point out. "If you cannot provide the exact environmental cues that fish experience in the wild, you reach hurdles that can only be overcome by hormonal induction therapies, such as Yonathan Zohar has been developing." Ninety-five percent of the time, he says, "our fish will not spawn without such assistance."
But maybe five percent of the time they do, which means that some individual fish in some families are getting the correct environmental signals. Woods points out, however, that he cannot get domestic fish to spawn with regularity. "Without hormonal therapies," he says, "we would be unable to continue our program." That's why his research is focusing on understanding just what kind of stress broodstock fish undergo. "Stress physiology is one area that we have to quantify with science," he says. Such quantification involves understanding the roll of diet.
Research has been underway to clarify the nutritional requirements stripers at different stages must have. For example, what are the amino acid requirements, the fatty acids that larvae, juveniles, or mature females need? "We are trying to develop effective diets for broodstock fish," he says, "so that they can make great gametes." These are major challenges. If commercialization is to really take off, says Woods, it will need an integrated operation.
"Domestication is the key," he reiterates. "Simply bringing in captive fish will not do it." Through domestication, he says, we'll have individual stripers that will enable us to provide more uniformity - "we won't have to catch wild fish, hoping they don't die on the way to the hatchery. We won't have to play Russian roulette anymore."