By David E. Boruchowitz
I saw my first vee of geese flying south this morning. I’ve heard a few before, but this is the first one I saw. For us in the Northern Hemisphere the geese are iconic of fall—shorter, cooler days and magnificent foliage. We are so linked to a climate with abrupt changes in temperature that we often think of the tropics as homogenous, unchanging. But the tropics have profoundly different seasons: dry and rainy.
In many ways this bipolar seasonal change is greater than the ones we experience. A fish that in the dry season hides in the leaf litter under a stream bank might be swimming among the leaves on high branches of mahogany and teak trees in the rainy season. Fishes are adapted to such changes that include factors like temperature, water chemistry, strength of currents, available foods, risk of predation, and spawning sites.
TFH contributor Ivan Mikolji has on his website photos of given locations in both the dry and the rainy seasons that illustrate nicely how different the habitats can become:
It is therefore a mistake to think of freshwater tropicals as inhabiting a stable habitat as reef fish do. Very few freshwater aquarium species experience the temperature extremes of a temperate climate, but they experience equally dramatic changes in their environment throughout the year. Our seasons govern when fish spawn, with many species needing a cooling period and then spawning when the temperature rises again. In the same way, tropical seasons typically determine when tropical fish spawn. Very often simulating some aspect of the dry-rainy cycle will persuade reluctant breeders. Increased water changes, plenty of live foods, and a slight drop in temperature may mimic the rainy season’s flooding, while decreased changes and a rise in temperature can simulate the dry season.
So, while our own seasonal changes have us checking heaters and putting up storm windows, they should also remind us that our fish might benefit from some changes in environmental conditions as well, especially if we’ve been frustrated trying to get them to spawn.