BROODSTOCK, SPAWNING, AND EGG HANDLING 189 



enumerated volumetrically if they are to be moved immediately to rearing 

 ponds. If they are held in rearing tanks or troughs until they accept formu- 

 lated feed, their numbers are estimated from weighed and counted samples. 



Egg Disinfection 



Eggs received from other hatcheries should be disinfected to prevent the 

 spread of disease. Disinfection should be carried out in separate facilities in 

 order to prevent contamination of the hatchery by eggs, water, trays, and 

 packing material from the shipping crate. 



The iodophor Betadine, can be used to disinfect most fish eggs. Eggs are 

 treated at 100 parts per million active ingredient (iodine) for 10 minutes. A 

 100 parts per million iodine concentration is obtained by adding 2.6 fluid 

 ounces of 0.5X Betadine per gallon of water. Betadine also is available in a 

 1% iodine solution. In soft water below 35 parts per million alkalinity, pH 

 reduction can occur, causing high egg mortality. Sodium bicarbonate may 

 be added as a buffer at 3.7 grams per gallon if soft water is encountered. 

 Should a precipitate be formed from the sodium bicarbonate it will not 

 harm the eggs. The eggs should be well rinsed after treatment. An active 

 iodine solution is dark brown in color. A change to a lighter color indicates 

 an inactive solution and a new solution should be used. Do not treat eggs 

 within 5 days of hatching as premature hatching may result, with increased 

 mortality. Tests should be conducted on a few eggs before Betadine is considered 

 safe for general use as an egg disinfectant. 



Largemouth bass eggs can be treated with acriflavine at 500 to 700 parts 

 per million or Betadine at 100 to 150 parts per million for 15 minutes. 



Roccal and formalin are not effective disinfectants at concentrations that 

 are not injurious to fish eggs. 



Incubation Period 



Several methods have been devised for determining the incubation period 

 of eggs. One method utilizes temperature units. One Daily Temperature 

 Unit (DTU) equals 1° Fahrenheit above freezing (32°F) for a 24-hour 

 period. For example, if the water temperature for the first day of incuba- 

 tion is 56°F, it would contribute 24 DTU (56°-32°). Temperature units 

 required for a given species of fish are not fixed. They will vary with dif- 

 ferent water temperatures and are affected by fluctuating temperatures. 

 However, DTU can be used as a guide to estimate the hatching date of a 



