The Biology and Culture of Tilapias

Disease Prevention and Control

Since tilapia culture is still largely undeveloped despite the great potential
of many of the species and their hybrids for culture in the developing coun-
tries, transglobal movements of fish are unfortunately still quite common.
Indiscriminate transfers of young fish for on-growing or as broodstock hold
dangers of many kinds. They have already led to problems from a fisheries
point of view in countries such as Australia (Moriarty pers. comm.) but
possibly even more significant, from the point of view of aquaculture and of
native fish stocks, is the risk of the transfer of microbial pathogens from one
area to another. Already two significant pathogens, Ichthyophthin'us multi-
filiis, and the iridovirus of lymphocystis (see above), have been introduced in
this way to stocks in Africa and Hawaii and, with increasing intensification
of farm systems, may become constraints on production.
Thus, there is justification on both disease prevention and ecological
grounds for national controls on stock transfers and importations. Where
no such national regulations exist, the prudent importer will insist on fry
importations being from a known and trusted source, will insist on heavy
formalin and malachite green treatment on the farm prior to export and will
perform similar prophylactic treatment within a secure and closed quarantine
water system, (isolated and downstream from any production facility)
within which such fish will be kept under close observation for at least a
month, prior to release into a production system.
Ideally, on disease grounds a country, region or even an individual tilapia
farm should be self-sufficient in fry production, but in view of the economic
and management justifications, it seems likely that as in many other live-
stock production systems, the industry will stratify into high quality fry
producers and fattening farms. The least that can be expected under these
circumstances is that the aforementioned minimal quarantine and hygiene
recommendations will be adopted as an insurance both for the individual and
his national fisheries ecosystem.
The indiscriminate use of antibiotics in tilapia culture is a subject of some
concern to medical and veterinary science. There is justification, on clinical
grounds, for the use of oxytetracycline, or the potentiated sulphonamides, at
therapeutic levels, in specific bacterial conditions. There is also some validity
in using these drugs, again at therapeutic levels, in the specific traumatic
situation involved in transporting large brood fish to overwintering facilities,
in sub-tropical countries. The practice of indiscriminate so-called prophylactic
use of antibiotics, however, is to be most severely deprecated and in view of
its significance in human pathogen drug resistance induction, should in the
authors' view be illegal in all countries. The use of the antibiotic chloram-
phenicol, which is the only reliable specific therapeutic for typhoid infections
in man cannot be condoned at any time in fish culture,

Acknowledgments

The work on diseases of tilapias at the Institute of Aquaculture of the

University of Stirling is part of a study of intensive tilapia culture techniques