Thirteen species of freshwater fish have been recorded in Tobago, but only a handful of these have successfully conquered the Main Ridge. While we humans can easily drive along the Roxborough – Parlatuvier road to access the reserve, fish must initially colonise inland from the sea. In North East Tobago, fish in the lower reaches moving upstream soon reach one of many waterfall barriers at the edge of the Ridge. Often these are tens of metres high, much like those at Argyll. Most fish will never manage to traverse these barriers, forever restricted to the lowland rivers. Only the most intrepid make it through to dominate the uplands.
Without a doubt, the king of the Main Ridge rivers is the Jumping Guabine, Aneblepsoides hartii. Ordinarily, this species reaches around 10cm from head to tail. However, the Main Ridge individuals are decidedly larger, as with fewer fish predators they can live longer.
Another advantage of jumping is that it allows hungry individuals to hunt prey, such as ants, that may be otherwise out of reach. Incredibly, they have been recorded jumping as high as 14cm, more than their total body length, to catch prey on overhanging vegetation or at the water’s edge. While in the water, they are ravenous predators of aquatic invertebrates, small fish and tadpoles.
A second species that has managed to breach at least some of the barriers and make its home in the Main Ridge streams is the Guppy or Millions-fish, Poecilia reticulata. Like the jumping guabine, these tiny (2-3cm) fish are also found almost everywhere in both Trinidad and Tobago and are usually seen in shoaling in large numbers in shallow water. Males are smaller and display vivid patches of orange, green and yellow, while the larger females are plain. Even from the river bank it is possible to watch males perform their distinctive ‘sigmoid’ courtship dance, which involves arching into an s-shape, raising their dorsal fin and intensifying their colouration in an attempt to seduce a female.
Many do not realise that the guppy, now world-famous in the aquarium trade and as a mosquito control agent, is named after a Trinidadian. Robert John Lechmere Guppy was an avid naturalist, and in 1866 sent samples of these pretty little fish to the British Museum in London where the species was initially named after him:‘Girardinus guppii’. The name was later changed when it was discovered that the same species had already been described from Venezuela, but the ‘guppy’ part stuck.
A third fish species that has defeated the Main Ridge boundaries has done so not by jumping or by reproducing fast after a chance introduction, but by actually climbing the cliff! Sicydium punctatum, also known as the Rock-climbing Goby or Tri Tri, reaches around 10cm long and feeds on algae in the streams of many of the Caribbean islands, as well as coastal regions of mainland South and Central America.
Although the Main Ridge supports only a few fish species, I’m sure you’ll agree that in this case it is a matter of quality over quantity, as the adaptations of those who manage to live in these streams are truly astonishing!