Researchers in Germany found fish exposed to artificial light during the night were bolder during the day.

In the lab, light pollution caused the test fish, guppies, to be more active at night. The artificial light also cause fish to emerge from their hiding places more quickly during the daytime.

The fish didn't become slower or lazier as a result of the increase in nighttime activity. Researchers found the guppies' swimming speed and social behavior was unaltered by light pollution.

A number of studies have documented the impacts of light pollution on animals and their ecosystems. The allure of a big city's bright lights can alter a bird's migration pattern. Light pollution can also interfere with coral's ability to spawn.

For the experiment, scientists exposed three groups of guppies to the same amount of light during the day and three different amounts of light at night. One group enjoyed complete darkness at night. The other two groups were exposed to different amounts of artificial light -- dim and bright.

Fish exposed to the brightest light were the quickest to leave their hiding spots during the day. The same fish spent more time swimming in the most exposed regions of the aquarium.

In the wild, bolder behavior could spell trouble for small fish.

"The consequences of this increased risk taking behaviour are difficult to predict, but it is possible that they could be more at risk of predation by birds or other fish," David Bierbach, researcher at the Leibniz Institute of Freshwater Ecology and Inland Fisheries, said in a news release.

Researchers detailed their work this week in the journal Scientific Reports.

"We suspect that the nocturnal light causes a stress response in the fish, and fish generally increase their risk taking when experiencing stress," said lead researcher Ralf Kurvers.

Underwater matchmaking: Scientists pair zebrafish mates by personality
Washington (UPI) Sep 21, 2018 - For zebrafish mates, the proper pairing of personalities is the best way to ensure reproductive success.

Scientists know both behaviors and appearance influence mate selection, but deciphering which factors are most important is difficult. To better understand the sexual selection process, scientists tested the reproductive success of fish paired by both personality and appearance.

"Our research explored both areas -- coloration patterns and personality traits -- to see if they were linked in some way and how they impacted the fitness of the species," Rey Planellas, a researcher at the University of Stirling, said in a news release.

To conduct their matchmaking experiments, scientists selected male and female zebrafish for four different combinations of personality and appearance. The groups included: bold fish with well-defined coloration; bold fish with undefined coloration; shy fish with clear coloration; and shy fish with unclear coloration.

Scientists allowed the different groups to breed and measure the reproductive success of each combination of mates.

"For all of the parameters of fertility and fitness of the species, proactive animals were the best, regardless of their external coloration pattern," said doctoral student Reynaldo Vargas, now working at the University of Panama. "However, both parameters were additive meaning that proactive fish with defined coloration patterns always achieved the best scores."

Researchers observed females guarding their eggs were most aggressively defended by bold mates.

Scientists descried the results of their breeding experiments this week in the journal PLOS One.

"Our research concluded that personality plays an important role that surpasses the effect of external appearance in the reproductive success ... and therefore, in the fitness of the species," Planellas said. "This is important in understanding the evolutive drivers for the ecology and conservation of fish, and for the industry to select specific phenotypes that will perform better. It may also inform how we select fish for aquaculture, and the potential impact upon conservation."

While being bold may boost reproductive success, the personality trait comes with risks. Previous studies suggest bold fish are more likely to put themselves in harm's way, while more reactive fish enjoy better survival rates.

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