Scientist discover concerning shift in behavior of tropical fish: 'Might push them over the edge'

As the oceans become warmer, tropical fish are moving south to cooler waters. 

According to The Conversation, tropical fish in Australia have been using the East Australian Current to move to more temperate reefs. These fish used to travel south in the summer, but the cold winter water would kill them — not anymore. The water's temperature has risen, and now these fish are surviving all year round. 

What's happening?

The study observed two temperate fish species and five tropical species across Australia's east coast. This area included both temperate waters and the tropics. The researchers used underwater cameras to look at how the fish reacted to threats, ate, and sheltered. 

The tropical fish were in new territory, so they had to adapt, while the temperate fish also had to adjust to the new species. 

The footage found that the tropical fish spent more time hiding to avoid predators. The researchers said they showed "lateralization," which is when the fish consistently turn left or right, helping them make faster escape decisions when threatened, per Phys.org. This method is helping keep them alive, but they aren't eating as much food. 

Some tropical fish are adapting by joining schools of temperate fish. It's believed that this is benefiting them because they are learning how to adapt to the environment, and there's safety in numbers. 

Why are changing migration patterns concerning?

While some of the tropical fish were adapting by joining schools of temperate fish, the native fish were not feeding as much when tropical fish were present. 

The researchers said: "That's worrying, because warming alone is already pushing many temperate species toward their biological limits. Adding new competitors might push them over the edge."

Fish in the Baltic Sea are also changing their behavior because of warmer water temperatures by eating the first prey that comes along. They require more calories when the water is warm because of increased metabolism, but by eating the first prey they see, they are missing out on larger prey that would provide more calories. 

What's being done about changing migration patterns?

The researchers said: "Understanding how fish respond to their new neighbors and how those responses shape who stays and who goes will be key to managing reefs in a rapidly warming ocean." 

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