A study of the genetics of the Amazonian giant cichlid genus Cichla has shown how naturally occuring hybrids are related to other species.
The Cichla are a notoriously difficult group of cichlids to identify and some experts believe that some of the fish considered to be distinct and undescribed species are in fact naturally occuring hybrids between other Cichla species.
To assess this, and to see how the different forms are related to one another, three geneticists from a Sao Paulo institution studied the chromosomes of several Cichla temensis, Cichla monoculus and a presumed hybrid between the two, and have just reported their findings in the journal Hereditas.
The fish were collected from three different locations in the central Amazon basin. The Cichla monoculus, C. temensis and their presumed hybrid, were caught in the Rio Uatuma, while further temensis were collected in the Jau and additional monoculus collected from the Solimoes (the name given to the main Amazon river downstream of Manaus).
The results showed that the two Cichla species and the natural hybrid collected from the Uatuma all had similar chromosomes, with a acrocentric structure and a diploid number of 2n=48.
They also each shared a single feature called a nucleolar organising region (or NOR) on the long arm of their chromosomes. However, in monoculus, the NOR was found on the second pair, in temensis it was found on the third pair, and in the hybrid C. monoculus X C. temensis, the NOR occured on either the second or the third pair.
For more details on the study see the paper: Neves Alves Brinn M, Ivan Rebelo Porto J, Feldberg E (2004) - Karyological evidence for interspecific hybridization between Cichla monoculus and C. temensis (Perciformes, Cichlidae) in the Amazon. Hereditas. 2004; 141(3): 252-7