Fish Hatchery Management - fisheries & aquaculture

BROODSTOCK, SPAWNING, AND EGG HANDI,IN(;heavy, mosslike growths of filamentous algae over the bottom do not prolengthof l-2 inches, an organic fertilizer suchduce good crops of suckers.After the suckers attain aas manure can be added to increase the production of natural food. Suckfeedsas a supplemental ers will adapt to formulateddiet.FATHEAD MINNOWThe fathead minnow occurs throughout southern Canada and in theUnited States from Lake Champlain west to the Dakotas and south toKentucky and the Rio Grande River. It feeds mainly on zooplankton andinsects. The spawning season extends from May until the latter part ofAugust. The eggs are deposited on the underside of objects in a pond, andhatch in 4.5 to 6 days. Mature fathead minnows range in length from ljto 4 inches, the male being consistently larger than the female. The lifespan of hatchery-reared fathead minnows is 12 to 15 months, depending onthe size of the fish at maturity.During the early spawning season a largemajority of the males usually die within 30 days after the onset of spawningactivities, and a large percentage of the gravid females will die within60 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 aspring or well. The ponds should not be larger than one acre or smallerthan 0.25 acre. The water depth should average about 3 feet and rangefrom 2 feet at the shallow end to 6 feet at the drain. The pond should beequipped with a controllable water inlet and drain. Ponds to be used forreproduction should be lined along two banks with rocks ranging in sizefrom 6 to 12 inches in diameter, or with tile, extending from six inchesabove the planned water level to two feet below it. This material providesspawning surfaces for the minnows.The brood ponds should be stocked in early April with about 60'lt adultminnows and 40'll immature fish. Both adults and juveniles are used asbreeders because of the species' short life span. In this way, one can besure of a continuous, uninterruptedsupply of newly hatched fry. Thebrood ponds should be stocked at the rate of 15,000 to 25,000 fish per acre.Fathead minnows normally start spawning activities during the latterpart of April or at a time when the pondwater temperature reaches 65'F.They spawn intermittentlythroughout the summer, provided the watertemperature does not rise above 85'F. When this temperature is reached,spawning ceases, and is not resumed until the pond is cooled by a weatherchange or by an increased flow of spring water. Withina few days ofspawning activity, small fry will be seen swimming near the surface, a few