The largemouth bass is a popular sport fish among anglers who know the familiar “knock” sound, but researchers at Southern Illinois University Carbondale are looking for better ways to make it viable for human consumption by firmly keeping the notoriously cannibalistic species out of their own diets.
With the help of a two-year, $324,000 grant from the U.S. Department of Agriculture, SIU researchers are working with Purdue University and local industry partner Big House Fish Farm to improve intensive largemouth bass aquaculture methods and produce a more productive and predictable yield. The study will be completed this fall.
Largemouth bass is not only a recreational fish but also one of the most popular food items, especially in Asian markets. Largemouth bass have been farmed for nearly a century, although the target market is usually anglers fishing in small lakes and reservoirs.
In southern Illinois, the market is growing, bringing in at least $3 million a year for local fish farmers, with potential for more, said Jim Garvey, director of the Center for Fisheries, Aquaculture and Aquatic Sciences at SIU and co-leader of the study with Habibollah Fakhraei, assistant professor of environmental engineering. The acceptance of largemouth bass as a food fish in live markets is relatively new, and raising them at high densities to maximize production in small ponds has presented challenges.
“Largemouth bass are the top predators in lakes and are not really adapted to life in high population densities,” Garvey said. “In the wild, they eat live prey and often eat each other. It’s not uncommon for a pond with lots of small bass to have one or two surviving large bass that have eaten their brothers and sisters.”
The aim of the research is therefore to find ways to increase the survival chances of largemouth bass by reducing cannibalism while encouraging the animals to eat prepared food.
A team effort
Working with Garvey on the project, which is taking place in nine ponds near SIU’s Touch of Nature Environmental Education Center south of Carbondale, are SIU research scientist Hannah Holmquist, research associate Asyeh Sohrabifar, postdoctoral fellow Giovanni Molinari and doctoral student Alexander “Koaw” Zaczek.
Zaczek said the team used three of the ponds to supply water to three 600-gallon tanks of largemouth bass. The researchers also divided three other ponds to keep the fish separate, while three other ponds housed control fish. The team is studying how the different husbandry methods affect the fish’s survival and growth.
Fences and nets prevent hungry predators such as otters, blue herons and great egrets from enjoying the buffet, which included more than 11,000 fish at the start of the project. Strict protocols govern the research team’s daily handling of the specimens and include feeding, cleaning, ventilation, waste disposal, equipment maintenance and other factors, Zaczek said.
Living in such close quarters, the team pays special attention to the nitrogen cycles in each enclosure, watching for signs of problems due to the waste products produced by the fish overwhelming the environment.
The team collects daily and weekly samples to conduct laboratory tests and monitor nutrient data and other factors, Zaczek said.
“We want to see, particularly in the split ponds, whether the ammonia produced by the fish waste is processed through the nitrogen cycle and has a positive effect on fish health compared to the control ponds,” he said. “Basically, we hope that the ammonia released by the fish is broken down into nitrite and then nitrate in the fish-free part of the ponds, so that the water returned to the pond’s fish contains minimal to no ammonia.”
Curb cannibalism?
In denser populations, it might be easier to encourage the fish to distribute their food more evenly across the population, Zaczek says.
“We try to get all the fish to feed early,” he said. “In a large pond where the fish are scattered, it’s harder to ensure consistent feeding, and it’s even harder to get the fish to feed early. The fish that start feeding early get a head start, grow bigger, and are more likely to eat their peers.”
When fish live in such conditions, cannibalism can certainly be detrimental to the bottom line. Eliminating this behavior in largemouth bass is a challenge, Zaczek said.
“Well, that’s easier said than done,” he said. “The hope is that the limited space and higher fish density will result in the fish accepting the food better and eating more similarly, which would also lead to similar growth rates. If they are the same size, they are less likely to eat each other.”
A growing market
As largemouth bass become increasingly popular in cooking, Zaczek said the team’s research could open up important revenue streams for fish farmers. If either the tank or split-pond method proves more efficient, farmers’ efforts could result in more fish surviving at more predictable sizes.
The success could also lead other fish farmers to try such methods on their own properties with other aquaculture species, such as catfish.
“Buyers are happier when the fish are a similar size, and sellers are happier when they can deliver more product,” he said. “As in most industries, efficiency is the goal in aquaculture.”
(Note to editors: Zazcek is pronounced “ZAY-check”; Asyeh Sohrabifar is pronounced “ah-SEE-yeh soh-RAH-bee-far.”)
