268 



FISH HATCHERY MANAGEMENT 



Table 37. physiological diseases, environmental factors implicated in 

 their occl'rrknce, and recommended mitigation procedures. (source: 



WEDEMEYEK AND WOOD 1974.) 



DISEASE 



STRESS FACTORS IMPLICATED 



MITIGATION PROCEDURES 



Coagulated yolk (white 

 spot) 



"Hauling loss" (delayed 

 mortality) 



Blue sac (hydrocoel 

 embryonalis) 



Rough handling; mala- 

 chite green containing 

 more than 0.()8"(i Zn'; 

 gas supersaturation of 

 I10"u or more; mineral 

 deficiency in incuba- 

 tion water. 



Hauling; stocking; rough 

 handling 



Crowding; accumulation 

 of nitrogenous meta- 

 bolic wastes due to 

 inadequate flow pat- 

 terns. 



Use "Zn-free" malachite 

 green (().()H"m Zn"); aer- 

 ate; add CaCi^ to 

 increase total hardness 

 to 50 ppm (as CaCOy). 



Add 0.1-0.3". NaCl dur- 

 ing hauling; add CaCl^ 

 to raise total hardness 

 to at least ,^0 ppm 

 (CaCOy). 



Maintain NH3-N concen- 

 tration lower than 1 

 ppm during egg incu- 

 bation. 



Use of malachite green is not recommended. 



results. All drugs and chemicals used to control infectious organisms can 

 be toxic to fish if concentrations are too high. All treatment calculations 

 should be double-checked before being implemented (Appendix G). In hu- 

 man or veterinary medicine, patients are treated on an individual basis 

 under carefully controlled conditions, whereas fish populations are treated 

 "en masse," often comprising hundreds of thousands of individuals. 



Treatment Methods 



There are two classes of treatments for fish disease, prophylactic and thera- 

 peutic. Prophylactic treatments are protective or defensive measures 

 designed to prevent an epizootic from occurring. Such treatments are used 

 primarily against ectoparasites and stress- mediated bacterial diseases. 

 Therapeutic treatments are begun only after disease signs appear. When 

 therapeutic treatments are needed to control external parasites or bacterial 

 gill disease, it may be a good indication of poor hatchery management. 



In fish diseases, as in human diseases, treatment with various medica- 

 tions and chemotherapeutic agents is for the purpose of keeping the 

 animals alive, i.e., for "buying time," not for killing 100% of the disease 



