This article originally appeared in the Newsday as part of the TTFNC's natural history series.
The rivers of Trinidad are home to six very distinctive types of catfish. These include armoured catfish such as the leopard-spotted ‘teta’ (Hypostomus robinii), the enigmatic ‘cascadu’ (Hoplosternum littorale) and the popular aquarium fish ‘pui pui’ (Corydoras aeneus). All tend to be bottom-dwellers and are grouped together as ‘cat’ fish on account of their barbels, which are sensory ‘whisker-like’ structures on their faces used to locate food. In Trinidad the fish most commonly referred to by the name ‘catfish’ is Rhamdia quelen, which unlike the species listed above, is silvery, unarmoured and scale-less.
The rivers of Trinidad are home to six very distinctive types of catfish. These include armoured catfish such as the leopard-spotted ‘teta’ (Hypostomus robinii), the enigmatic ‘cascadu’ (Hoplosternum littorale) and the popular aquarium fish ‘pui pui’ (Corydoras aeneus). All tend to be bottom-dwellers and are grouped together as ‘cat’ fish on account of their barbels, which are sensory ‘whisker-like’ structures on their faces used to locate food. In Trinidad the fish most commonly referred to by the name ‘catfish’ is Rhamdia quelen, which unlike the species listed above, is silvery, unarmoured and scale-less.
An adult catfish - Rhamdia quelen Rhamdia is found throughout much of Central and South America, from Mexico to Argentina. In T&T, it is especially common in the rivers of the southern slopes of the Northern Range, but is found throughout the country, with the exception of Trinidad’s north coast and the whole of Tobago.
Like many catfish species, Rhamdia possess mildly venomous spiny rays on their pectoral and dorsal fins, which are used for defence against larger predatory fish. The barbels on either side of their face help them locate food in dark or murky waters, such as their preferred prey of small fish. However, their varied omnivorous diet also includes insects, zooplankton, plant matter and crustaceans.
Like many catfish species, Rhamdia possess mildly venomous spiny rays on their pectoral and dorsal fins, which are used for defence against larger predatory fish. The barbels on either side of their face help them locate food in dark or murky waters, such as their preferred prey of small fish. However, their varied omnivorous diet also includes insects, zooplankton, plant matter and crustaceans.
Rhamdia especially favour the shadowy waters underneath bridges. They tend to hide under rocks or dead wood during the day, emerging into the open at night to feed. Incredibly, one population has taken its preference for shadowy habitats to the absolute extreme – the dark depths of the Cumaca Caves!
Catfish were first described as dwelling within these Northern Range caves, which are more famous for their oilbirds, in 1926. For many years people believed these cave fish to be a completely different species, named Caecorhamdia urichi, as they were virtually blind, had lost much of their pigmentation and had considerably shorter barbels. However, recent studies suggest that these pale, sightless catfish are simply a ‘troglomorphic’ (cave-adapted) form of Rhamdia, who have invaded the cave and adapted to the unusual conditions. This invasion appears to have happened on at least two separate occasions and deserves further investigation. Indeed, the late Professor Kenny began some preliminary observations which suggested that the cave catfish were remarkably flexible in their traits – for example, when exposed to sunlight, some of their pigmentation would begin to reappear.
Catfish were first described as dwelling within these Northern Range caves, which are more famous for their oilbirds, in 1926. For many years people believed these cave fish to be a completely different species, named Caecorhamdia urichi, as they were virtually blind, had lost much of their pigmentation and had considerably shorter barbels. However, recent studies suggest that these pale, sightless catfish are simply a ‘troglomorphic’ (cave-adapted) form of Rhamdia, who have invaded the cave and adapted to the unusual conditions. This invasion appears to have happened on at least two separate occasions and deserves further investigation. Indeed, the late Professor Kenny began some preliminary observations which suggested that the cave catfish were remarkably flexible in their traits – for example, when exposed to sunlight, some of their pigmentation would begin to reappear.
 A catfish inside the Cumaca caves - only those deep in the cave are unpigmented |  The caves are more famous for their noctural 'oilbirds' |
Whether cave or river-dwelling, catfish fertilisation occurs externally. This means that the female will lay tiny eggs in the water (each less than 3mm diameter), which the male will then fertilise with his sperm. After just 48 hours these will hatch into fry after which they continue to grow rapidly. Young Rhamdia often have a distinctive dark stripe along their body which fades in the adult fish. If you ever manage to catch a Rhamdia (which is almost impossible using a net, thanks to their preference for hiding in small, dark spaces), chances are it will be a female, as scientists have shown that there tend to be twice as many females as males in the average population.
A young Rhamdia quelen - not in a cave In the Cumaca Caves, I have only seen small specimens, but in the rivers adult rhamdia can reach lengths of nearly half a metre. This makes it the largest catfish in Trinidad, but nothing in comparison with their Asian relative, the Mekong giant catfish which can grow to nearly 3 metres long! At the other end of the spectrum, the parasitic ‘candiru’ catfish from the Amazon is just a few centimetres long and is feared for rumours that it occasionally swims up the human urethra causing excruciating pain. However, whether such anecdotes are true remains a matter of debate.
Several species of Trinidadian catfish are caught for food – including Rhamdia, teta and cascadu. Others are collected to be sold and bred in the pet trade – such as pui pui. However, a much greater threat to the diversity and distribution of our catfish species is the destruction of their riverine habitats, especially in the Northern Range. For example, the famous Cumaca Cave is situated near to one of the many quarries that are systematically destroying the ecosystem from which we still have so much to learn. Let us ensure that these fascinating fish will be around for a long time to come – who knows what discoveries are still to be made.
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