By Richard Harbison Woods Hole Oceanographic Institution The potential of the butterfish, Peprilus triacanthus, as an agent of biological control in the Black and Caspian Seas By Richard Harbison Woods Hole Oceanographic Institution

The butterfish, Peprilus triacanthus, is specialized to feed on gelatinous organisms

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Peprilus triacanthus has a number of morphological features that seem to be adaptations for feeding on gelatinous organisms 1. The jaws are specialized for biting, not for feeding on crustacean zooplankton. 2. The teeth are specialized for cutting. 3. The stomach is large, with a very long intestine. 4. A specialized structure, the pharyngeal pouch, probably functions like the spines in the throats of molids, acanthurids and sea turtles, serving to grind up and retain gelatinous material. 5. It is behaviorally adapted for hovering.

The morphology of the butterfish, Peprilus triacanthus The morphology of the butterfish, Peprilus triacanthus. Note pectoral fin used for hovering, the non-protrusible mouth, and the location of the operculum.

The pharyngeal pouch is located in the front of the esophagus, directly behind the gill rakers. It is lined with teeth, the bases of which appear as star-shaped objects

This is one of the inward-pointing teeth that line the walls of the pharyngeal pouch.

Peprilus feeding on Mnemiopsis

There is a synergistic effect when several butterfish feed on Mnemiopsis

The butterfish feeds on other gelatinous organisms, such as the medusa, Aurelia.

Note the movements of the mouth as the medusa is consumed

Rates of feeding by Peprilus on jellyfish are extremely high Rates of feeding by Peprilus on jellyfish are extremely high. Starved fish can consume over three times their body weight in an hour in short-term experiments

In these experiments, Peprilus triacanthus were starved, and then fed an excess of jellies. The feeding rate stabilized at a level of between 1 and 2 times body weight per hour

In these 40-hour experiments, fish consumed their body weights in Mnemiopsis every hour, on average.

This means that a single 0 This means that a single 0.3 kg butterfish can eat over 200 kg of Mnemiopsis leidyi in 1 month Should butterfish be successfully introduced, they would have a marked effect on populations of Mnemiopsis. Since they are a delicious fish, they would provide a new fishery resource. There is little risk that they would become pests, since commercially valuable resources are usually overexploited.

Peprilus triacanthus and Peprilus paru in a U.S. fish market

The ability to reproduce in the Black and Caspian Seas is unknown Laboratory experiments show that the fish can survive short-term exposure to salinities as low as 3.5 However, sampling data show that most eggs and larvae are found offshore Experiments are needed on long-term survival rates under conditions resembling those of the Black and Caspian Seas

Successful acclimatization of the butterfish is probably more likely in the Black Sea than in the Caspian Sea Pelagic eggs More closely matches home range Wider variety of food organisms Less environmental stress

Should this plan be adopted, here are some immediate research needs Development of long-term maintenance techniques (artificial food, environmental optima, etc.) Development of transport techniques More studies on feeding behavior, environmental tolerance and physiology Establishment of facilities in Black or Caspian Seas

Potential Disadvantages of a Successful Introduction of the Butterfish Add another exotic species to the system If the fish creates a problem, it would be difficult to eradicate Diseases or parasites could be introduced inadvertently

Advantages of a Successful Introduction of the Butterfish Reduce Mnemiopsis populations Provide a new fishery resource Could restore indigenous fisheries