BROODSTOCK, SPAWNING, AND EGG HANDLING 185 



the best of the methods evaluated. The displacement method takes twice 

 the time required by either of the other methods. The weight method is 

 recommended when large lots of eggs must be enumerated, while the dis- 

 placement method is more desirable with small lots of eggs. 



Another method of egg inventory, which differs from other volumetric 

 methods basically in egg measuring technique, sometimes is used by fish 

 culturists. Eggs are measured in a container, such as a cup or strainer filled 

 to the top, and an equal number of containerfuls of eggs are put in each 

 egg incubator tray or jar. Sample counting consists of counting all the eggs 

 held in one measuring container. To get accurate egg inventories, the same 

 measuring unit must be used for the sample counts as for measuring the 

 eggs into the incubator. Measurement by filling the container to the top 

 eliminates errors in judgment. This method gives a good estimate of the 

 total number of eggs, but does not estimate the number of eggs per fluid 

 ounce. 



Several methods have been used for the estimating number of striped 

 bass eggs. Estimates can be made by weighing the eggs from each female 

 and calculating the number of eggs on the basis of 25,000 per ounce. The 

 eggs can also be estimated volumetrically on the basis of Von Bayer's table. 

 Largemouth bass and catfish eggs are measured by weight or volumetric 

 displacement. 



Various mechanical egg counting devices have been developed that use 

 photoelectric counters (Figure 63). The eggs are counted as they pass a 

 light source. Velocities producing count rates of up to 1,400 eggs per 

 minute have proven to be accurate. Air bubbles, dirt, and other matter will 

 interfere with accurate counting and must be avoided. 



Salmonid eggs should be physically shocked before egg picking (removal 

 of dead eggs) commences, after the eggs have developed to the eyed stage. 

 Undeveloped or infertile eggs remain tender and they will rupture when 

 shocked. Water enters the egg and coagulates the yolk, turning the egg 

 white; these eggs then are readily picked out. Shocking may be done by 

 striking the trays sharply, siphoning the eggs from one container to 

 another, or by pouring the eggs from the incubator trays into a tub of 

 water from a height of 2 or 3 feet. Care should be taken to make sure that 

 the eggs are not shocked too severely or normally developing eggs also may 

 be damaged. (Figure 64). 



Numerous methods for removing dead eggs have been in use in fish cul- 

 ture for many years. Before the introduction of satisfactory chemical fungi- 

 cides, it was necessary to frequently remove (pick) all dead eggs to avoid 

 the spread of fungus. In some instances where exposure to chemical treat- 

 ments is undesirable, it still is necessary to pick the dead eggs. 



One of the earliest and most common methods of egg picking was with a 

 large pair of tweezers made either of metal or wood. If only small numbers 

 of eggs are picked, forceps or tweezers work very well. Another device in 



