Reintroduced conserved fishes susceptible to parasites

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A study published in the most recent issue of the journal Conservation Biology has found problems associated with the ex situ conservation of fishes.

Using the guppy (Poecilia reticulata) as a model, Cock van Oosterhout, Alan Smith, Bernd Hnfling, Indar Ramnarine, Ryan Mohammed and Joanne Cable studied the effects of inbreeding and susceptibility of captive-bred fish to parasite infestation upon reintroduction to the wild.

The authors used two populations of guppies from Trinidad to study different conservation breeding regimes: one population from the upper Aripo drainage has a small effective population and is genetically isolated (simulating many endangered natural populations), while the other from the lower Aripo drainage has a much larger effective population and is more genetically diverse.

The three captive breeding regimes that were studied are: (1) inbreeding fish crossed with their full siblings, (2) minimized inbreeding, which avoided consanguineous (i.e. full sibling) matings, and (3) control group that were allowed to cross at random.

The results showed that over four generations, the body sizes and fertility of guppies were significantly reduced due to inbreeding depression.

The researchers then released captive-bred fishes (after four generations in captivity and free of parasite infestations) into a mesocosm in Trinidad (eight artificial ponds on the banks of the Naranjo tributary), and studied the effects of captive breeding on the survival rate and infestation by parasitic gyrodactylid worms (Gyrodactylus turnbulli and G. bullatarudis).

The authors found that captive-bred guppies were extremely susceptible to gyrodactylid parasites (58% survival rate) compared with their wild counterparts (96% survival).

They postulate that a reduced level of immunogenetic variation due to inbreeding and lack of exposure to natural parasites may have rendered captive-bred individuals more prone to infectious disease.

In concluding, the authors suggest that for reintroduction of captive-bred organisms in any conservation programme, ...prior exposure to parasites before release could reduce parasite induced mortality rates. In addition, the gradual release of captive-bred individuals should be preferred over en mass reintroduction because it limits the density of susceptible individuals and probability of parasite outbreak.

For more information, see the paper: van Oosterhout, C, AM Smith, B Hnfling, IW Ranmarine, RS Mohammed and J Cable (2007) The guppy as a conservation model: implications of parasitism and inbreeding for reintroduction success. Conservation Biology 21, pp. 1573"1583.