Glowing fish shine light on fish stocking success at UAPB

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By Milthon Lujan

USA.- Glowing fish are helping researchers at the University of Arkansas at Pine Bluff Aquaculture/Fisheries Center of Excellence shine light on the success rates of sport fish stocking in some Arkansas lakes. Thanks to the application of a fluorescent dye, those in the field may be better able to measure the effectiveness of certain fish stocking programs in the state, says Greyson Farris, graduate student of aquaculture/fisheries at UAPB.

“Stock enhancement is the process of raising fish in a hatchery and releasing those fish to a pond, lake or river to add to existing fish populations or to create a population where one previously did not exist,” he said. UAPB regularly works with the Arkansas Game and Fish Commission to ensure the utility and successfulness of its stocking programs, which provide fishing opportunities to anglers across the state.”

Farris said stock enhancement research covers a diverse range of topics including the creation of new fisheries, altering the genetic diversity of fish populations and the rebuilding of commercially viable marine fish stocks. At the most basic level, however, the objective of stock enhancement research is to determine whether stocked fish are contributing to the fisheries in which they were released.

“When we sample a population that has been supplemented with stocked fish, we look for the proportion of the total catch that is made up of stocked fish,” he said. “Ultimately, we hope to see stocked fish surviving, as the purpose of stocking fish is to contribute positively to the population.”

Farris said the process of assessing the success of fish stockings is tedious by nature and traditionally involves many hours spent both in the field and laboratory. Recently, however, populations of crappie that emit a fluorescent green glow when placed under a black light may help prove that the process does not always have to be such a headache.

Chemical marks have been used in stock enhancement research for decades, he said. When marking fish, researchers have commonly used the antibiotic chemical Oxytetracycline hydrochloride (OTC), which produces fluorescent marks on the internal calcified structures of the fish. Because workers can never be sure if they are netting an OTC-marked fish in the field, they have to spend many hours in the lab, dissecting sacrificed fish and examining internal bone structures to determine their origins.

“Calcein is a fluorochrome dye – not an antibiotic – that can be used as a helpful, time-saving alternative to OTC, as it produces visible external marks on fish that appear fluorescent under appropriate light,” Farris said. “This means that fish marked with calcein can be viewed non-lethally in the field, which allows for near real-time estimates of stocking success.”

Using calcein, researchers can collect fish at a stock enhancement site and calculate the proportion of the sample that is comprised of stocked fish on the spot, he said. The benefits of using the fluorescent dye are twofold – it saves both time and the lives of fish that would otherwise be killed during the study.

“The task of analyzing fish that are potentially OTC-marked in the lab would typically take months and hundreds of man-hours, while sampling a population of calcein-marked fish takes a day or two since the marks are visible on the surface of the fish,” Farris said. “Instead of being sacrificed, the sampled fish can continue to contribute to the total population of the fishery.”

In trials at UAPB during fall 2015, researchers studied the AGFC’s crappie stocking program using fingerlings raised at the Joe Hogan State Fish Hatchery in Lonoke, Arkansas and the William H. Donham State Fish Hatchery in Corning, Arkansas. Ninety-six thousand black crappie and 86,000 white crappie were treated in a calcein-water solution after first undergoing a salinized water application and fresh water rinse.

After being marked with the calcein solution, the crappie were stocked in eight Arkansas lakes in late 2015. Black crappie were stocked in Calion Lake, Beaverfork Lake, Irons Fork Lake and Sugarloaf Lake, while the white crappie were stocked in Lake Saracen, Lake Des Arc, Lake Poinsett and Lake Charles. As part of this research, Farris conducted five samples of each lake to determine the survival of calcein-marked fish and the proportion of the population made up of stocked fish.

When sampling the eight lakes in the study, Farris nets crappie with one of the AGFC’s standard half-inch bar mesh trap nets, which consists of a rectangular frame net with a mesh wing that extends from the body of the trap net to the shoreline. The fish travel vertically and longitudinally to shallow depths in the morning and evening, and when they come across the mesh wing, they follow it along the length of the wing and swim into the net, where they are trapped.

“Our calcein observation technique is simple and can be executed at any time of day,” he said. “We simply use a three-millimeter contractor trash bag to create a locally dark environment and observe fish inside the trash bag with a pair of special barrier filter glasses and an ultraviolet light.”

Sampling a stock enhancement lake typically takes a few days, as researchers aim to catch 200 crappie for a sample, Farris said. As soon as the fish are observed for calcein marks, they are returned to the water.

Farris said one of the drawbacks to the use of calcein in stock enhancement studies is its tendency to become less visible on a fish’s body over time. Exposure to sunlight entering the water causes the mark on the fish’s surface to degrade.

“Our work indicates calcein marks on the external surface of crappies held at our hatchery last a little longer than a year,” he said. “External marks could last longer in the field, because lakes are often deeper than our experimental tanks and sunlight penetration decreases as water depth increases.”

As he continues to test calcein’s effectiveness in stock enhancement research projects, Farris said he plans to keep a group of calcein-marked fish at UAPB for at least two years to determine how long the marks will last.

Farris received an award for his research on the use of calcein in stock enhancement research at the 18th Biennial Research Symposium of the Association of 1890 Research Directors in Atlanta, Georgia. He won second place in the Animal Health and Production and Animal Products category for his oral presentation titled, “Calcein Marking: A Non-Lethal Batch Marking Option for Stocking Evaluation.”

Source: UABP News


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