The monkeyface prickleback hides under tidal boulders on the California coast and feasts only on algae. It could offer a lifeline to aquaculturists seeking to reduce their reliance on fishmeal-dependent carnivores such as salmon.
Plant-eating fish like the prickleback are quite rare: Only about 5 percent of the 30,000 documented fish species are herbivores. The aquaculture industry is trying to make carnivores imitate herbivores – and reduce reliance on fishmeal from wild fisheries – by creating plant-based feeds that appeal to them.
The algae-eating prickleback offers an alternative, but farmers have yet to commercially raise the eel-like fish, which grows up to three feet long and weighs six pounds. With flesh that tastes delicate and mild, the prickleback sometimes appears on the seafood menus of San Francisco, California-based restaurants as monkeyface eel.
Herbivorous fish such as the prickleback have to be really good at digesting plants to extract the lipids, which are essential for life. While animal matter is at least 30 percent lipid, plant matter is only 5 to 10 percent lipid.
To uncover clues about the prickleback’s digestive acumen, a group of scientists sequenced its genome. The scientists found that the prickleback has extra copies of particular genes that grant them five copies of a certain enzyme that breaks down plant-based lipids. Most fish only have two copies of the enzyme.
“That makes them good at actually digesting these lipids,” University of California, Irvine Professor Donovan German told SeafoodSource. German co-authored a study on the prickleback’s genome that was recently published in the Proceedings of the Royal Society B.
"When you look at their genome, there's a clear reason for it, and the reason is they have an extra copy of these genes," German said.
The prickleback, or Cebidichthys violaceus, used to range from Oregon down to Baja California, but now only lives north of Santa Barbara because of human impacts to the coastal zone. It is prolific in the dangerous intertidal areas where waves crash roughly and birds and snakes hunt. People catch them using a method called poke pull fishing, in which a pole affixed with a baited hook is worked into the watery areas under tidal boulders.
"Especially when there are boulders, they're really common. You start turning over boulders and you start seeing all these eel-like fish," German said.
Fish farmers could turn to the prickleback as the next aquaculture species, or they could at least seek out species that have a similar ability to digest plants, by comparing those genomes to the prickleback’s, German said.
"We could either try to genetically modify species that we currently want to raise, like salmon, and we could put the right genes in them that allow them to eat plants. Or, we could switch over to species that eat plants," German said. "It's probably cheaper and more efficient to go with ones that can already do this."
"What I think would be more fruitful is to sequence more genomes of plant-eating fish and see if they have these abilities, and start culturing them," German added.
The prickleback would be fairly easy to raise – all it wants is something to hide under, such as a PVC pipe in a tank. However, it does take a few years for the prickleback to reach full size, German explained.
"I could see that being the argument against doing them on a large scale, and maybe focusing on something that grows a little faster," German said.
Photo courtesy of the University of California, Irvine
