Nathan Egnew, a graduate student of aquaculture/fisheries at the University of Arkansas at Pine Bluff, is researching the physiological response of largemouth bass to ammonia. His research could help fish farmers raise and transport the fish to market more efficiently, he says.
By Will Hehemann Special to The Commercial
“As commercially-sold fish grow and eat in ponds, they release waste that contains ammonia,” he said. “If the buildup of ammonia in a pond is not controlled through regular water changes or the addition of nitrifying bacteria, ammonia can reach toxic levels.”
“High environmental ammonia” designates ammonia concentrations that threaten the survival of fish, Egnew said. This type of ammonia is a common problem on farms, as producers raise fish in increasing densities.
“It is well understood that to avoid toxic ammonia levels, fish farmers should lower their feeding rates; however, this is only a short-term fix,” he said. “For commercial producers, feed availability must be maximized to grow their fish to a marketable size in a reasonable timeframe. In this scenario – when lowering the feeding rate is not economically feasible – there is an urgent need to develop strategies that help alleviate high ammonia-induced toxicity.”
All fish species have different responses to toxic ammonia, Egnew said. Some species are more sensitive to ammonia, while others are more resistant.
“To date, no relevant information exists on the physiological response of largemouth bass to ammonia,” he said. “Therefore, it is vital for farmers producing largemouth bass to know the resilience of their fish to ensure they are well kept and healthy until harvest.”
Egnew said his research focuses on the ways largemouth bass alter their physiology in response to elevated ambient ammonia.
“If the mechanisms through which largemouth bass deal with ammonia are better understood, it will be easier to devise short-term and long-term solutions for helping them cope with ammonia-induced stress,” he said. “These solutions could help producers ensure the health of the fish as they grow in ponds and during their transport to market.”
As he finalizes his research on the response of largemouth bass to ammonia toxicity, Egnew is planning the next phase of his project.
“In Arkansas and most other states, the main source of water for fish culture comes from deep underground water resources, which are often high in iron content that can also prove toxic for fish,” he said. “Our plan is to test the effects of ammonia on fish cultured in water with high iron content. We hope to determine whether the adverse effects of ammonia are amplified or even possibly reduced by the presence of iron.”
In February 2018, Egnew won an award for his research at the World Aquaculture Society’s Aquaculture America meeting in Las Vegas.