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The Circumtropical Swarm Population of the Longspined Porcupinefish (Diodon holocanthus Linnaeus)

by John E. Randall, Caroline S. Rogers & John C. Ogden – aqua 25 (2) pp. 53-80

Evidence is presented that Diodon holocanthus is a circumtropical swarm (not a hybrid swarm because the individuals are not hybrids). Some individuals are so different
from one another in both color and morphology that they appear to be different species. Thirty undersea and aquarium photographs from different global localities are provided to demonstrate the variability. The worldwide distribution is achieved by the juvenile that has been found more than 1,000 km offshore as large as 90 mm SL. How can it feed on zooplankton with jaws and dentition designed to crush shelled invertebrates? We believe it draws the prey into the mouth with the same mechanism that it uses to expand its body when threatened; the water with prey is diverted to the pharyngeal cavity, then released from the gill opening on each side. Larger juveniles may seek concentrations of zooplankton for feeding, perhaps collectively. A confirming experiment in an aquarium is advised. Aggregations of pelagic juveniles have been observed at the surface outside barrier reefs and found inshore the following morning, indicating that settlement took place at night to minimize predation. The juveniles soon disperse to inshore habitats of mangrove and sea grass to coral reef. The hybrid Diodon holocanthus x D. hystrix from South Africa is illustrated. The narrative for the present research on D. holocanthus is presented chronologically to show how increasing evidence failed to support the multitude of apparent new species of Diodon, leading to the conclusion of a swarm.

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