Tiny Mandarin Fish Reveal Surprisingly Complex Spawning Ritual

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Larger male mandarin fish are far more successful at mating than smaller ones. Yet the researchers discovered that the smaller males don't appear to have a strategy for enhancing their reproductive opportunities, which may affect the viability of populations in the wild.

"Usually when you have great differences in mating success among males, smaller males develop alternative mating tactics, like 'sneaking' or 'streaking,' in which smaller males rush up to a spawning pair and release sperm in the hope of some fertilizations," Rasotto explained.

The researchers found that when the larger males are removed, female mandarin fish spawn with smaller males—but reluctantly.

Courtship takes longer. The females are more inclined to end the mating dance before spawning has occurred, requiring a second or third attempt. In addition, the mating pairs are more vulnerable to predators as they rise to complete the act.

Declining Populations

Aquarium owners and fishermen are usually interested in catching larger specimens of mandarin fish and other ocean spawners. Besides directly depleting the fish populations, this makes fewer males available for spawning, which leads to lower reproduction rates.

The researchers say their findings show the importance of understanding the reproductive biology of a species to better predict how it will be affected by harvesting pressures. "It was only by looking in detail at both the reproductive biology as well as the ways in which the fishers actually target the fish that we realized what was happening and the implications for the targeted population," Sadovy said.

Thousands of fish are removed every month from very limited areas, she noted. Many aquarium collectors, Sadovy said, incorrectly believe that the fish they purchase won't live long and can be replaced easily because there are plenty of fish in the sea.

"Many of the lovely reef fishes in the marine aquarium trade are treated like cut flowers, dying soon after they are purchased, then simply being replaced," she said.

But many reef fish can live for years or even decades, said Sadovy. It is the methods by which the fish are caught, transported and ultimately cared for by consumers that is often to blame for high mortality rates among aquarium fish, she explained.

Some environmentally aware businesses have sprung up to supply the aquarium trade while minimizing fish mortality.

"Whether or not the marine aquarium trade is a benefit, by creating interest and concern in reefs and reef fishes, or a menace to reef fish populations of desired fish species, will depend on using our understanding of these populations and managing the fisheries," Sadovy said.

"There is much promise, but this has yet to be realized," she added. "Traders and consumers have an important role to play by demanding fish (be) caught only using sustainable practices."

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