288 FISH HATCHERY MANAGEMENT 



Immunization of Fishes 



In the past few years there has been rapid development in the technology 

 of fish vaccination, primarily for salmonids. In the 1977 Proceedings of the 

 International Symposium on Diseases of Cultured Salmonids, produced by Ta- 

 volek, Inc., T. P. T. Evelyn thoroughly reviewed the status of fish immuni- 

 zation; excerpts of his report are presented in this section. 



Pressures conspiring to make vaccination an attractive and almost inevit- 

 able adjunct approach to fish health were probably most acutely felt in the 

 United States where it was becoming increasingly clear that reliance on the 

 use of antimicrobial drugs in fish culture might have to be reduced. First, 

 the list of antibacterial drugs that could legally be used is extremely 

 small. ..and the prospects for enlarging the list were dim. Second, the effec- 

 tiveness of the few available antibacterial drugs was rapidly being dimin- 

 ished because of the development of antibiotic resistance among the 

 bacterial fish pathogens. Third, there was the danger that this antibiotic 

 resistance might be transmissible to micro-organisms of public health con- 

 cern, and because of this there was the very real possibility that drugs now 

 approved for use in fish culture would have their approval revoked. 

 Finally, viral infections in fish could not be treated with any of the antibi- 

 otics available. 



Faced with the foregoing situation, American fish culturists were forced 

 to consider other measures that might help to ensure the health of their 

 charges. One obvious approach was immunization. Advantages of immuni- 

 zation were several. First, immunization did not generate antibiotic resis- 

 tant micro-organisms; second, it could be applied to control viral as well as 

 bacterial diseases; third, it appeared that fish may be vaccinated economi- 

 cally and conveniently while still very small; and fourth, protection con- 

 ferred by vaccination was more durable than that resulting from chemo- 

 therapy, and could be expected to persist for considerable periods follow- 

 ing vaccination. Finally, with killed vaccines, at least, the requirements for 

 licensing the vaccines were less stringent than those required for the regis- 

 tration of antimicrobial drugs. 



Unfortunately, the biggest single factor working against the widespread 

 use of fish vaccination was the lack of a safe, economical and convenient 

 technique for vaccinating large numbers of fish. Recent advances in sal- 

 monid immunization are very promising. 



Vaccination Methods 



Attempts at oral vaccination have been unsuccessful, and alternative pro- 

 cedures have been devised: mass inoculation; infiltration; and spray vacci- 

 nation. 



