58 MAINTAINING FISHES 



the female into a suitable container, adding sperm 

 similarly pressed from a mature male and gently 

 brushing the milt over the eggs with a feather or the 

 anal fin of the male. A short time following fertiHza- 

 tion, the eggs should be spread out and excess milt 

 and mucous carefully washed away. The eggs must 

 then be incubated at a suitable temperature and aera- 

 tion until they hatch. Dark or cloudy eggs are dead 

 and should be removed since their presence may en- 

 courage the growth of fungus. 



Anesthetization of Fishes 



It is sometimes desirable to anesthetize fishes 

 prior to working with them, or it may be desirable to 

 anesthetize them to decrease the diflficulty of captur- 

 ing them from aquaria. Carbon dioxide either as com- 

 pressed gas, dry ice, or from the addition of sodium bi- 

 carbonate followed by the addition of sulfuric acid 

 diluted 1 to 500 (for further details on the bicarbonate 

 method see Fish 1942) is an effective anesthetic espe- 

 cially suited to permit capture of fishes in aquaria. 

 Fishes are anesthetized at concentrations above 150 

 p.p.m. Anesthesia occurs in a matter of minutes; fishes 

 satisfactorily recover at lower concentration but wiU 

 die if permitted to remain in high concentrations of 

 carbon dioxide. An anesthetizing concentration of 

 carbon dioxide can be removed from water by one or 

 two hours of aeration. 



Quinaldine, a coal tar derivative, is an inexpensive 

 and effective fish anesthetic. At seven p.p.m. it wiU 

 quickly incapacitate fishes and keep them incapaci- 

 tated for extended periods of time. Upon being re- 

 moved from the quinaldine solution, the fishes recover 



