How hot weather affects fish

Vietnam is heading into the hottest days of the year, so Lộc wants to share a few things about how hot weather can affect your water and your fish, and what you can do to adapt.

**Low dissolved oxygen**

The higher the water temperature, the lower the dissolved oxygen. Specifically: 15 mg/L at 0ºC and 8 mg/L at 30ºC. To avoid a shortage, you can bump up aeration to generate more dissolved oxygen. Cooling methods that planted-tank keepers use also work well: chillers, USB fans blowing across the surface, air-conditioned rooms, wall fans.

**Biological processes run faster**

Higher temperatures speed up the fish's metabolism, so fish grow faster and breeding intervals shorten. Eggs that take 3-4 days to hatch in cool weather only need 2-3 days in this heat. The free-swimming fry stage shortens too. Likewise, fry get hungry faster and you can feed them more. **However**: eggs also fungus up and spoil faster (because fungus also grows faster).

**Chemical processes run faster**

Chemicals in the tank react with each other more readily. This ties directly into the biological side — fish eat more, digest and waste more, so more toxins are produced.

**Fish get more "hot-headed"**

Just as people are more quick to anger in hot weather, fish also fight more when the temperature is high (high meaning higher than the cool season — not, you know, boiling). Those shifting environmental conditions also alter fish behavior. For most species this is also breeding season, so they're influenced by sexual hormones and become more aggressive.

Just a little something to share with fellow hobbyists.