Gouramis

It appears amazing that a fish can suffocate. Yet this is absolutely what happens in some species, for example gouramis, if they are averted from surfacing customarily to take in a swallow of atmosphere.

Gouramis have developed to exist in waters that can end up being particularly level in oxygen. Under such conditions, most fish could sooner or later gag to passing. In gouramis, however, some of the gills have developed into special organs that are very efficient at absorbing oxygen directly from the

air.

The Price of Survival

This survival strategy comes at a price, though, since the highly modified gills can no longer absorb oxygen from the water. Therefore, even if there is an ample supply of dissolved oxygen in the water, gouramis cannot obtain as much as they need through their gills. They must regularly come to the surface to breathe. If they cannot do this, they will die. Many species also use air to blow mucus-covered bubbles. During the breeding season the males of these species build bubble nests on the surface, or under a submerged leaf. Eggs are laid in these bubbles and develop in an oxygen-rich environment.

In other species, males carry the eggs in their mouths until they are ready to hatch. Since these males must come to the surface for air, the eggs also receive plenty of oxygen, even if there is little dissolved oxygen in the water. In the breeding season, males become very aggressive. In some species of fighting fish this aggression lasts all year. In the Far East, fish-fighting contests between these fish are held,with bets placed on the outcome.