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Taking Spadefish from ‘New Species’ to ‘Aquaculture Species’

November 29, 2011
11-day-old spadefish larvae are only the size of this letter "a." ©Janet Krenn/VASG

11-day-old spadefish larvae are only the size of this letter "a." ©Janet Krenn/VASG

By Kate Schimel

Under a microscope, baby Atlantic spadefish look cartoonish, with huge, translucent eyes that dwarf their teardrop-shaped bodies. They hardly resemble the beautiful, striped plate-sized fish they’ll become.

Michael Schwarz, a seafood extension specialist at Virginia Tech, sees a lot of possibility in these tiny fish. “Spadefish is what I coin a potential emerging species,” he says. Schwarz is leading a Virginia Sea Grant-funded team, collaborating with researchers at VIMS and the Southern Illinois University at Carbondale, to look at the spawning and food needs of the Atlantic spadefish. Studies like these are the first step towards developing a new species for aquaculture.

The aquaculture industry is always hungry for more fish as it races to keep up with ballooning demand, especially in the U.S. where there’s a seafood trade deficit of more than $9 billion annually. But the research required to make aquacultured fish profitable and on the dinner table can be painstaking.

Dan Sennett stands in a VIMS green house where hundreds of tiny spadefish are swimming in 12 plastic tanks. ©Janet Krenn/VIMS

Dan Sennett stands in a VIMS green house where hundreds of tiny spadefish swim in plastic tanks. ©Janet Krenn/VIMS

When I visit the spadefish in the VIMS Marine Finfish Lab, they are only eleven days old and the size of this letter “a.” Dan Sennett, Schwarz’s co-investigator who is responsible for the spawning and care of the fish in their larval stage, shows me around the greenhouse where the little fish are kept. Keeping these fish alive in this onshore environment is a constant challenge. At this stage, they are so sensitive that sunscreen residue from my hand would be enough to disrupt their development. Then there’s the weather you can’t plan for, like the June thunderstorm that flooded the greenhouse and temporarily knocked out the power. “These things swim in my cerebellum,” Sennett says a little wearily. “It’s hard to keep larvae alive under these conditions.”

Two rows of plastic tanks hold the fish, which have just graduated to the second phase of feeding trials. They are now eating brine shrimp, leaving behind the microscopic animals called rotifers that they ate when they were first hatched. Sennett is experimenting with six different combinations of rotifer and brine shrimp food.

A Good Aquaculture Fish
Before a species can be grown commercially, it has to undergo extensive lab trials to work out how to spawn, feed, and care for it. Streamlining the process enables commercial growers to make a profit.

Sometimes the very lifecycle or behaviors of finfish can thwart this effort. In the lab, a species may refuse to reproduce, and fish can even begin to eat each other. Spadefish, however, seem to be unusually well suited to the confined, onshore environment.

“There’s lots of things that make this fish a very interesting and unique candidate,” says Schwarz. “These guys like to swim in schools. They like to stay near structures; so behaviorally they are very amenable to confinement…and with what we’ve seen so far, they’re not cannibalistic.”

As for their place in the wider seafood economy, Schwarz says, “It has potential as a foodfish animal, as a marine ornamental for the aquarium industry, and there’s also potential for stock enhancement.”

Stock enhancement, the practice of releasing farm-raised fish to build up the wild population, can be used for restoration purposes and also to make more fish available to recreational fishermen. Spadefish is already a popular recreational fishing target in the Chesapeake Bay—owing its popularity to the fight it gives to anglers as well as its tastiness.

Ask Schwarz, an angler himself, about how to cook an Atlantic spadefish and he gets a hungry look in his eye. “You can just gut it and scale it, and then batter it and deep-fry it,” he says. “It’s an incredibly good eating fish.”

Schwarz believes the fish would be a great addition to restaurant menus, but because spadefish hang around structures in the water, it’s hard for commercial fishermen to get substantial volumes for regular sale. “For a restaurant to put something on the menu, they need to make sure they can get it for several weeks at an absolute minimum, for larger chain restaurants even longer,” Schwarz explains. An aquacultured spadefish would be able to provide the consistency needed for a commercial product.

Answering the Diet Question
In a few months, when the larval fish have matured to the juvenile stage, they will be moved to the Virginia Tech–VSAREC to undergo another round of feeding trials, this time with manmade pelleted feed. Co-investigator Jesse Trushenski at Southern Illinois University will produce feed with varying levels of proteins and lipids to identify requirements for each.

This is a crucial step in the process, as the health and commercial success of the fish is dependent on determining the correct quantities of proteins and lipids. Too much or too little of either can cause health problems in the fish and leave them vulnerable to disease, but some combination of the two will produce the best growth. Also, says Schwarz, “lipids and proteins are the most expensive ingredients, so we need to identify the right amount very quickly” to minimize costs while maximizing production.

Another challenge is getting the spadefish’s dietary amino acids right. Unlike other aquaculture species, spadefish eat invertebrates, such as jellyfish. This may make it difficult to use currently available fish feed, which is made from fish oil and fishmeal (from vertebrate animals). Looking into alternative food sources requires investigation beyond the reach of this study, but Schwarz suggests this different diet may actually be a good thing.

“As global [human] populations increase and food consumption increases, there’s greater and greater demand for a limited supply of fishmeal and fish oil,” he says. “Future expansion in aquaculture will be hinged on species where we can reduce the use of dietary fish meal and fish oil.”

All these feeding trials are necessary because of spadefish’s relative newness as an aquaculture species. Only one earlier study, conducted by Sennett and Mike Oesterling (VirginiaL Sea Grant Aquaculture Specialist, now retired), investigated how to spawn spadefish, and there have been no known studies looking at feeding habits.

At this early stage, Sennett is optimistic about the outcome of this work. The adult fish that spawned the small fish in the greenhouse are larger than many of their relatives in the wild, and the larvae are healthy and growing. “This is the best spawn [of spadefish] we’ve had,” Sennett says.

When he looks at spadefish, Schwarz sees economic opportunity for Virginia. “There is a strong potential for aquaculture in Virginia,” Schwarz says. “Once you produce the products locally, it goes into the value chain. You can have local processing; you can have local wholesaling. Local aquaculture feeds into all of that.”

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