The Zebra Otocinclus is probably the most spectacular and most attractive Otocinclus species for the aquarium hobby. It has been known for some time that there are two forms of the species described in 2004 as O. cocama: one from the lower Río Ucayali and another one from the Río Tigre. Both rivers are tributaries to the Río Marañón, which ultimately flows into the Amazon. While the Ucayali form, on which the description is based, has been exported for the aquarium trade since around the turn of the millennium, it is mainly the Tigre form that has been on the market in recent years, at least in Germany. Both populations can be clearly distinguished by their stripe pattern. The question of whether the populations can also be distinguished morphologically and genetically, and thus also whether they are merely variants of one species or two distinct species, was investigated by Eduardo MEJIA and Roberto E. REIS and recently published.

Otocinclus cocama, Ucayali, © Ingo SEIDEL

Otocinclus cocama, Río Tigre, © Ingo SEIDEL

The authors conclude that the two populations of O. cocama are composed of one lineage that differs only slightly in body size and shape. Although molecular methods show two separate lineages, both populations are genetically very similar and individuals from both populations are found in one of the lineages. This suggests that the two populations are still interbreeding or have only recently separated.
Breeding of O. cocama in the aquarium has already been successful several times (see for example the photo series on planetcatfish.com), but a detailed breeding report does not seem to have been published yet. According to the data in the publication by Mejia et al., it is likely that the two populations can be crossed – therefore they should better not be kept together in the aquarium during breeding attempts, in order to preserve the specific pattern of the individual populations in aquarium strains.

Citations:

• Mejia, E. & Reis, R. E.
  Molecular and morphometric data provide evidence of intraspecific variation in shape and pigmentation pattern in Otocinclus cocama (Siluriformes: Loricariidae) across major river drainages
  Journal of Fish Biology, 27 Dec. 2023
  https://doi.org/10.1111/jfb.15639
• Reis, R. E.
  Otocinclus cocama, a new uniquely colored loricariid catfish from Peru (Teleostei: Siluriformes), with comments on the impact of taxonomic revisions to the discovery of new taxa
  Neotropical Ichthyology 2(3), Sept. 2004
  https://doi.org/10.1590/S1679-62252004000300001

Text: Achim WERCKENTHIN – Bilder: Ingo SEIDEL