Fish and Thunderstorms

Storms have an effect on our fishy friends (Kevin Rank @ flickr)

Ever wondered why your fish always seem to be more active right before a thunderstorm? Bettas will build larger bubblenests. Loaches swim more frantically than normal. Tetra start breeding behavior. This isn’t just coincidence. Our fish do react to changes in the weather. 

Male golden gourami (Trichopodus trichopterus)
attending to bubblenest (Alberto Garcia @ flickr)

 Most fish in the hobby come from tropical waters where there are only two seasons: wet and dry. During the dry season, the water recedes and all the fish are cramped together. Competition for food and shelter is high. The dry season is ended by huge rainstorms, sometimes called monsoons. These, like any thunderstorms, are preceded by a huge drop in barometric pressure which fish can sense using their swim bladders. Through the millennia fish have learned that these huge drops in the air pressure mean rain and therefore more water is coming. This reduces the competition for food and shelter. With more resources, the parents won’t be in strong competition with their offspring. The adults can reproduce without fear that their offspring won’t be able to find enough food.

Fish also associate the drop in air pressure with reduced visibility at a later time. Storms and heavy rains will dirty up the water both by wave action and the runoff from the hills. As many fish are sight-predators and can’t hunt in murky waters, the drop in air pressure sets off an insane hunger drive. In the wild they ravenously feed until the water starts getting muddy or the thunder scares them into hiding. They do this because the water has can stay muddy for a few weeks at a time depending on the severity of the storm.

Sight predators like oscar (Astronotus ocellatus) and many cichlids have
high food food drives before a storm (Brynja Eldon @ flickr)

So while we may have taken the fish out of the wild, we still can’t take part of the wild away from the fish. Whenever the barometric pressure begins to drop, they still think the monsoons are coming!