MIRES: What is your opinion of the use of antibiotics as prophylactics? Why do you say
use these during fish transfers only?
ROBERTS: Well, antibiotics work and they are very important, but I am very fearful for
the future of mankind if we carry on the way we are with the use of antibiotics. Anti-
biotics have revolutionized medicine, but aquaculturists, in attempting to revolutionize
protein production, are going well on the way towards preventing us from keeping
our ability to use some antibiotics, particularly in regions like Southeast Asia. Antibiotics
are active against human bacterial pathogens as long as they are used at an adequate
dosage. If they are used at lesser dosages, this selects for antibiotic-resistant strains. They
can also pass on this resistance to completely different bacteria during reproduction. The
most serious prospect is that aquatic bacteria in culture systems receiving low dosages of
prophylactic will pass this resistance to human pathogens or animal bacterial pathogens.
In manured farms, of course, we have very large amounts of human and animal enteric
pathogens. In Southeast Asia, the development of drug-resistant strains of typhoid and
cholera are serious possibilities.
MIRES: What about limited use of antibiotics during fish transfers, for example between
tanks?ROBERTS: Responsible culturists will of course use antibiotics sensibly and carefully in
such situations, but in the developing countries, people don't understand the risks.
It is very difficult to explain to a fish farmer in a developing country who has saved
some fish with antibiotics why he should not continue low level treatments all the time. I
can easily envisage the first chloramphenicol-resistant typhoid strain (and this is the only
drug we have against typhoid) arising from its misuse in, for example, Southeast Asian
catfish culture in ponds receiving human or animal wastes. Now, as far as using antibiotics
during transfer, the first thing is, particularly for species such as silver carp which have
very delicate skins and are big and very active fish, it is almost impossible to transport
them without significantly damaging their skin. Also tilapias, particularly the large
individuals with big strong spines can damage each other's skin and suffer spine breakage.
It would, therefore, seem reasonable to treat such fish either by adding antibiotics to the
transport water or as a pre-treatment by food incorporation to lessen infection of these
lesions caused by transportation. I must stress, however, that this must be done with
effective therapeutic levels of antibiotics, not lesser amounts. Again, I stress the dangers
of the development of resistant strains of animal and human pathogens through ineffec-
tive dosage.