comparison of pathogens found on wild caught and hatchery raised striped mullet, mugil cephalus, juveniles

An outcome of the development and improvement in hatchery technologies for the mass production of marine fish species is the use of farmed raised individuals for growout in open ocean cages or their releases as part of an effort to enhance depleted wild stocks. One public concern that has been raised is whether farm raised fish might harbor some pathogen(s) that would possibly infect wild stocks upon their introduction.

To investigate this possibility striped mullet juveniles both produced in the hatchery and caught from the wild (approximately three inches in total body length) were examined for bacterial, protozoan and metazoan pathogens.

Of the different categories of pathogens that were found, the hatchery- produced juveniles did not have any metazoan parasites. This is logical because larger parasites are distributed by direct transport to a particular location.

Although hatchery produced juveniles were found to possess fewer microbial pathogens (i.e., bacteria and protozoans) the majority were present on both. Two points need to be emphasized from the results.

First, even though the hatchery activities are often undertaken in isolated areas, by no means can it be considered a sterile environment. Secondly, the individuals chosen did not show any signs of disease and were classified as “normal and healthy”.

This clearly illustrates that many of the pathogens that afflict the striped mullet in captivity are already present in the hatchery. Although a particular disease/parasite may be the direct cause of morbidity or mortality, outbreaks are usually a secondary result of other factors such as a lowering of resistance due to chronic low levels stress and finally succumbing to a particular pathogen.

This situation also occurs in humans as there are a host of “pathogens” that make up the normal flora in our digestive tract but only express themselves when our natural defenses are compromised in some way. From this preliminary screening it would appear that the probability of having a disease transmitted from cultured fish to wild fish is minimal.

For more information please contact

Clyde S. Tamaru, Sea Grant Extension Service, Tel: 956-2869, fax: 956-2858, e-mail: ctamaru@hawaii.edu

(article by C.S. Tamaru, Hawai’i Sea Grant Extension Service; J. Brock, Aquaculture Development Program; W. FitzGerald Jr., Pacific Rim Consultants; V. Sato, Anuenue Fisheries Reseach, Center ; in Makai Sea Grant College Program, Vol. 23, N° 4, April 2001)

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