The cascadura, Hoplosternum littorale, is a very popular fish in Trinidad and Tobago, and holds a sacred place in the country's folklore. The demand for it far exceeds the supply, and as such, it has become ever more popular as a culture species. It is found naturally from northern South America to Central America; it occurs locally in the lower reaches of most of the rivers south of the Northern Range.

The cascadura has its own protective armour: the body is covered with two rows of bony platelike scales. The eyes are not well developed because they are not of much use in the dark murky waters where the fish lives. The cascadura uses its two pairs of sensitive 'whiskers' (barbels) to detect its food. Another important feature of this species is its ability to utilize its gut, richly supplied with blood vessels, to assist in breathing when the water becomes low in oxygen. The fish surfaces and gulps air, a characteristic that makes it vulnerable to sharp-eyed fishermen. Males grow to a maximum of about 200 mm (8 in) and females to about 150 mm (6 in).

Fishermen venture into the freshwater swamps in the dry season when water levels are receding and accessibility is good. The main fishing gear is the castnet, but occasionally hook-and-line or trapping methods are used. Some people go to the extreme of blocking off areas of water and pumping or bailing until fish can be picked up by hand.

The fish is marketed live or on strings, and is occasionally seen frozen at some of the larger food outlets. The price of the live fish is highest during the rainy season when catches are at their lowest. Cascadura are seasonal breeders and nest-building coincides with the flood rains of the rainy season. The nest consists of floating debris supported by a mass of air bubbles in which the fertilized eggs are deposited. The nest is guarded by the male which grows a curved spine on its pectoral fin during the breeding season. Sometimes fishermen go into the swamp and catch the guarding males. This action leaves the nest exposed to predators. In addition, people sometimes take the egg masses for food. These practices plague the now dwindling natural stocks. Although no scientific stock assessment has been carried out, accounts from fishermen confirm that catches are constantly decreasing while catch efforts increase.

The flood rains enable the newly hatched fry to disperse, but large numbers are eaten by the larvae of some insects (such as the batty mamzelle) or by other fish. Within a year, that is, by the following rainy season, the surviving fish develop into mature reproductive adults. Feeding activity is greater at night; the diet is varied and consists mainly of rotting vegetation and small living organisms.

It is essential to know the biology and behaviour of the animal before attempts are made to culture it under controlled artificial conditions.

At the Institute of Marine Affairs, the cascadura has been spawned and reared to marketable size for a number of years. Its Aquaculture staff offer advice to farmers through the Technical Advisory Services of the Institute, and through two aquaculture manuals. The first of these (Fish Farm Ponds: Design, Construction, Maintenance) describes how to build and maintain the pond; the second (Cascadura Farming: From Hatchery to Production) covers all aspects of culture, including nest collection and preparation, hatching the eggs, nutrition and feeding, nursery tank and pond maintenance, harvest and post-harvest treatment.

There are a number of features about the cascadura that make it suitable for culture. It is not bothered by the low levels of dissolved oxygen that often occur in the swamp waters, as it gulps fresh air from the surface. Cascadura is not aggressive, so can be grown at fairly high densities in ponds; it may also be grown with other species (polyculture). It is not very susceptible to disease, and its predators are known and can generally be controlled. Its life cycle is simple, and it normally has good survival rates from the hatchery. Cascadura accepts artificial pelleted rations readily and attains marketable size in a relatively short space of time. Most important, there is a very strong demand for the fish and it fetches a good market price.

The successful culture of the cascadura should ensure that this fish will always be found in Trinidad's waters, thus preserving its place in the folklore of our country!

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