BROODSTOCK, SPAWNING, AND EGG HANDLING 141 



heavy, mosslike growths of filamentous algae over the bottom do not pro- 

 duce good crops of suckers. 



After the suckers attain a length of 1-2 inches, an organic fertilizer such 

 as manure can be added to increase the production of natural food. Suck- 

 ers will adapt to formulated feeds as a supplemental diet. 



FATHEAD MINNOW 



The fathead minnow occurs throughout southern Canada and in the 

 United States from Lake Champlain west to the Dakotas and south to 

 Kentucky and the Rio Grande River. It feeds mainly on zooplankton and 

 insects. The spawning season extends from May until the latter part of 

 August. The eggs are deposited on the underside of objects in a pond, and 

 hatch in 4.5 to 6 days. Mature fathead minnows range in length from 1^ 

 to 4 inches, the male being consistently larger than the female. The life 

 span of hatchery-reared fathead minnows is 12 to 15 months, depending on 

 the size of the fish at maturity. During the early spawning season a large 

 majority of the males usually die within 30 days after the onset of spawn- 

 ing activities, and a large percentage of the gravid females will die within 

 60 days. One- to two-inch immature fatheads, even though only a year old, 

 die shortly after they become gravid at an age of about 15 months. Thus, 

 the older fish in a pond should be used as forage after they have spawned. 



Ponds for fathead minnows should have flowing, cool water from a 

 spring or well. The ponds should not be larger than one acre or smaller 

 than 0.25 acre. The water depth should average about 3 feet and range 

 from 2 feet at the shallow end to 6 feet at the drain. The pond should be 

 equipped with a controllable water inlet and drain. Ponds to be used for 

 reproduction should be lined along two banks with rocks ranging in size 

 from 6 to 12 inches in diameter, or with tile, extending from six inches 

 above the planned water level to two feet below it. This material provides 

 spawning surfaces for the minnows. 



The brood ponds should be stocked in early April with about 60% adult 

 minnows and 40"n immature fish. Both adults and juveniles are used as 

 breeders because of the species' short life span. In this way, one can be 

 sure of a continuous, uninterrupted supply of newly hatched fry. The 

 brood ponds should be stocked at the rate of 15,000 to 25,000 fish per acre. 



Fathead minnows normally start spawning activities during the latter 

 part of April or at a time when the pondwater temperature reaches 65°F. 

 They spawn intermittently throughout the summer, provided the water 

 temperature does not rise above 85°F. When this temperature is reached, 

 spawning ceases, and is not resumed until the pond is cooled by a weather 

 change or by an increased flow of spring water. Within a few days of 

 spawning activity, small fry will be seen swimming near the surface, a few 



