DNA Barcoding completes life cycle

The catfish Clarias gariepinus is an important aquaculture species because of its rapid growth rate and resistance to handling and stress. In many African countries, C. gariepinus is an important solution to the increasing demand for fish and fish products in response to rapid human population growth, the declining productivity of capture fisheries, and the fear of animal-related disease outbreaks (e.g., avian, bovine, and swine influenza). This has made the catfish a potentially important source of protein and economic growth in many rural and urban communities involved in the fishery industry.

However, the catfish is host to several parasites that might threaten its viability especially in captivity. One of those parasites is the flatworm Tylodelphys mashonense, whose resting larvae occur in the cranial cavity of the fish. The species goes through three hosts during his life cycle. An intermediate snail host and the fish would be its second intermediate host before it moves to its final bird host. Unfortunately, details of this life cycle are poorly understood. The intermediate snail host(s) remain unknown and the range of avian hosts is also not well characterized, apart from the grey heron Ardea cinerea, the type host.

An international team of researchers now used DNA barcoding to link cercariae and sporocysts with adults and metacercariae collected in Tanzania (both Mindu Dam, Morogoro, and Mwanza Gulf, Lake Victoria). Sequences from cercariae infecting Bulinus spp. matched those acquired from metacercariae from Clarias gariepinus, and those from adult Tylodelphys mashonense from the grey heron Ardea cinerea and the white egret Egretta alba.

In conclusion, the successful linking of the life cycle stages of T. mashonense from the Tanzanian freshwater bodies using molecular tools has underlined the usefulness of this approach in unravelling the complex life cycles of digenetic trematodes in the absence of experimental establishment. As a consequence, the control of Tylodelphys species parasitizing C. gariepinus, one of the most suitable species for aquaculture, may become possible.