Yellow perch is a staple of Lake Erie restaurant menus, with menu boards along the shore advertising everything from classic fish fry to local specialties. While most of these fish were likely caught in the wild, some of them will have come from aquaculture: fish farms throughout the Great Lakes region raise yellow perch, and aquaculture sales in Ohio tripled from $1.8 million to $6.6 million in 2010.
As with all agriculture products, selective breeding – a process in which parents are selectively bred to enhance specific desired traits in their offspring – has improved production and led to most of the fruits, vegetables, and farm animals we know today. Corn kernels are larger and more uniformly colored than those produced by ancient corn plants, dairy cows produce more milk than their ancestors, and commercial bananas are larger and sweeter than their ancestors, to name just a few examples of genetically improved species.
Researchers at the Ohio State University’s South Centers in Piketon, partially funded by Ohio Sea Grant, are now selectively breeding yellow perch to thrive in aquaculture operations, but they’re using modern technology to give them an edge: genetic analysis. Dr. Han-Ping Wang and his colleagues are using DNA markers to separate sibling fish, thereby avoiding inbreeding that can negatively affect future generations by slowing growth rates and making fish more susceptible to disease. When combined with more traditional selection of favorable traits like size and overall health, this approach leads to a marked improvement in growth and resilience for the fish.
Now in the third generation, these improved yellow perch can reach their marketable size of 8.5 inches about 30% faster than unimproved fish, in 12 or 13 months instead of 18 months. “One of the reasons is that they genetically utilize the feed better,” explains Wang, Director and Principal Scientist for the Ohio Aquaculture Research & Development Integration Program (OARDIP) at OSU South Centers. “So that means they use the same amount of feed, but they can reach market size in a shorter time. And that saves a lot of time, a lot of labor, a lot of feed, and a lot of cost.”
To test the potential success of this new line of yellow perch in a commercial setting, the researchers are currently conducting on-farm and on-station tests at the Ohio Center for Aquaculture Research & Development (OCARD) and at Mill Creek Perch Farms in Ohio, at the University of Wisconsin’s Northern Aquaculture Demonstration Facility, and at Coolwater Farms, LLC in Wisconsin. These locations provide a wide range of climates in which to raise the experimental fish, from southern Ohio (at latitude 39) to northern Wisconsin (at latitude 46).
Rearing protocols, which outline a consistent way of raising the fish from hatchlings to adults, were the same across locations to make sure results could be compared easily. The fish arrived at the farms as eggs, in long ribbons that contain about 20,000 eggs each. Those ribbons were placed in small containers kept at around 53° Fahrenheit, and the eggs hatched in two weeks. From there, the baby fish (called fry at this point) were transferred to a small pond containing cultured zooplankton to feed them during this early life stage.
“After six weeks, we harvest the fish, we now call them fingerlings, and bring them to indoor tanks for feed training,” Wang says. In the natural environment, juvenile and adult perch eat other fish, and need to be trained to accept commercial food pellets. This usually takes about three weeks, and then the fish can be returned to outdoor ponds to continue growing.
Genetically improved perch were raised in two ponds at most locations, along with unimproved local fish in two additional ponds. “The problem with this separate rearing is that sometimes it’s not a good approach,” Wang says. “If one pond gets much higher survival rates, that means in that pond, the density of fish is higher as well. That also means there is less feed, because we calculate the feeding amount based on the estimated survival rate, but if one pond got a higher survival rate, our original calculation of feed is much less than what the fish need.”
This is what happened in both on-station tests: while the researchers assumed a 75% survival rate for all of the fish and based the amount of feed given on that number, the improved perch had a survival rate of 92%, 30% higher than the local fish. This means the fish actually got much less food and less oxygen, however, they still grew about 30% faster than unimproved fish with less variation in size. These higher growth and survival rates also resulted in 30-40% higher production from ponds with improved fish.
To address the density problem, one farm location used “communal rearing,” raising improved and unimproved fish together in the same ponds. Before the hatchlings were placed into those ponds, the researchers determined the genotype of the parent fish, using eight unique genetic markers that would later allow them to determine which adult fish came from the local strain, and which were offspring of the genetically improved line.
“In that case, there’s no environmental effect, because both kinds of fish grow up in the same pond,” Wang explains. “And our results from the parentage analysis, looking at the genetic markers, show that in this case, our improved fish grow 32% faster than the unimproved fish.”
Faster growth and more uniform size at the end of the culture period would be a definite advantage for fish farmers who traditionally raise perch for 18 months to have only about 50-60% of the slow-growing fish be of a size suitable for sale. “Our improved fish grow faster, so at the end of that culture period, the percentage of marketable size fish will be much higher,” Wang says. In addition, most of the fish will reach marketable size more quickly, in about 12 or 13 months, allowing farmers to sell them earlier.
Once the commercial market for these fast-growing fish is established, the number of farms growing yellow perch for food could rise quickly, as fish is valued as a lean and healthy protein source for a human population that continues to expand. With this in mind, Wang and his colleagues, along with Ohio State University’s Technology Commercialization and Knowledge Transfer office, are exploring opportunities for widely distributing the genetically improved perch once commercial-scale testing is complete.
“Farm-testing our fish is a part of the process for future commercialization,” says Wang. “But there are other things we need to consider as well, including how we can distribute these fish to farmers. Other agriculture species that already have genetically improved lines, such as salmon and tilapia that also began as research programs, some of the researchers partnered with large companies to distribute fish. The university’s Office of Technology Transfer already came down last year to our location to discuss how to do that, so we have several thoughts.”
Those ideas range from patenting the technology to applying for intellectual property rights that can then be transferred to a commercial company, as well as running a joint venture between the university and an industry representative. One large agriculture company has already expressed interest in the genetically improved fish, but final decisions will have to wait until all tests and evaluations are completed.
Another potential hurdle for commercialization is shifting the way people currently think about the yellow perch that are grown in Great Lakes aquaculture. Right now, many fish farms provide fish that are stocked in lakes and ponds in Ohio, Michigan, and Indiana, to replenish perch populations for recreational anglers or to restore populations that have been depleted by fish kills. For that purpose, fish don’t need to be genetically improved, as their final size doesn’t have to conform to specific market expectations. Genetic contamination, the flow of genes from a domestic or invasive species to native populations, is also a concern for stocking improved fish to natural water bodies.
However, yellow perch that grow more quickly on a smaller amount of feed, increasing the overall profit margin of raising perch directly for food, would make aquaculture more attractive to farmers who have previously been discouraged from investing in perch culture or expanding their current operations.
According to the Great Lakes Fishery Commission, more than 2.8 million pounds of wild yellow perch were harvested from Lake Erie in 2011, in both commercial and recreational fisheries. Not only could aquaculture have positive economic impacts on Ohio and the Great Lakes region, but it would also reduce the stress that fishing for yellow perch can place on the Lake Erie ecosystem. Management agencies work hard to maintain a sustainable fishery, but increasing the profit margin for cultured yellow perch could remove this potential strain from an ecosystem that already has a lot to deal with, and offer both ecological and economic benefits for the entire Great Lakes region.