A population of small reef fish hiding amongst the spines of sea urchins in the Banggai Archipelago, doing their best to avoid capture by the hands of ornamental fish collectors, may now depend on their captors to ensure existence in the wild. The Banggai cardinalfish (Pterapogon kauderni) are in trouble as result of their unique life history and the aquarium industry’s insatiable demand for the fish. However, these exact attributes may also bring P. kauderni back from the brink of extinction.
Banggai cardinalfish are easily identified by their three distinct vertical black bars on pearly silver bodies. This color pattern is thought to be a form of camouflage that helps them hide among urchin beds, giving the fish its Bajo name bebese tayung, meaning “little fish in the sea urchin” . Additional speckling and stripes come together to create an extravagant display contrasting the fish’s monochromatic color scheme. Interestingly, each individual of P. kauderni has its own unique white speckling pattern across its body. The unique patterns allow biologists to identify individuals in large schools for research purposes, similar to how shark biologists use dorsal fin notches to identify individual sharks.
The reproductive biology of P. kauderni sets them apart from other fish. Unlike most small reef-associated fish, P. kauderni are a mouthbrooding species with direct development, meaning they have no free-floating larval stage . The female releases around 50 eggs per clutch with each egg measuring approximately 3 mm in diameter . Once three quarters of the eggs have been released by the female, the male quickly begins gulping up the eggs into his mouth, never letting them reach the ground. Then, both the male and female defend an area of 50-60 cm in diameter, not letting any other individuals come close to their spawning site. This marks the beginning of the incubation process. The male keeps the eggs in his mouth, rotating them, passing water through them, and protecting them for around 30 days. The eggs hatch in his mouth and the male releases the juveniles, now fully formed miniature versions of the adults, at 6–10 days post-hatch.
P. kauderni are an endemic species of the Banggai Archipelago, east of Sulawesi, Indonesia . The lack of a pelagic, free-floating stage in the life history of P. kauderni plus its low fecundity result in a small geographic range of 9460 km2, or about the size of Yellowstone National Park, with little chance of further dispersal . P. kauderni become attached to their surroundings and rarely venture far from home, never straying more than 1 m off the ocean floor. Even with high site fidelity to a relatively small range, local populations of P. kauderni tend to be genetically distinct from one another, and this may be related to small spatial structures in their habitats that act as barriers between individual populations .
At the time of writing, P. kauderni are endangered, meaning the species faces a “very high risk of extinction in the wild” . This is largely due to a growing demand for them from the ornamental fish aquarium trade after the fish’s rediscovery by the scientific community in 1994. These fish were then sold to an international marketplace of marine ornamental fishes worth between $90–300 million USD in annual retail sales .
However, thanks to captive breeding and sustainable aquaculture, the aquarium trade may be the answer to saving wild populations in Sulawesi. With improving technology and better methods of rearing them in captivity, survivorship of captive-bred juvenile P. kauderni is increasing tremendously , providing a new source of fish for the aquarium trade. This success means lower collecting pressure on the already delicate wild populations and also a possibility of reintroduction. P. kauderni is currently one of the most widely available, captive-bred marine aquarium fish; this huge captive population could one day be used to replenish wild stocks in the Banggai Archipelago if numbers there continue to decrease.
John Liu is an undergraduate student in the Department of Wildlife, Fish, and Conservation Biology at UC Davis. His current research examines common characteristics that contribute to data deficiency in sharks and he hopes to use that information to better manage conservation efforts. John spends his free time caring for his saltwater reef aquarium and tweeting about it on his twitter account, @TheJohnLiu.
Main featured image by Nicolas Bourré [Source]
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