achieved by placing nylon fiber mats in the ponds to 

 serve as a place for the fish to deposit their eggs. 

 Experiments conducted at the Fish Culture De- 

 velopment Center at Marion. Ala., during the past 

 several seasons, have indicated a promising prefer- 

 ence for the use of the mats by the largemouth bass, 

 Micropterus sulmoidcs. After the eggs are depos- 

 ited, the mats are removed and placed in hatchery 

 tanks where the required care and protection can be 

 given them. This is nothing more than a modem 

 adaptation of the ancient Chinese practice of placing 

 brush mats in known spawning areas to collect carp 

 eggs. 



A principal limitation to higher yield of warmwa- 

 ter species in hatcheries has been the problem of 

 providing natural food. To accomplish this, ponds 

 are fertilized. Intensive fertilization can produce 

 enough natural food organisms in static ponds to rear 

 up to 550 kg offish from a hectare of water in a single 

 season. Supplementary feeding can increase this up 

 to about 2,500 kg. O.xygen limitations in lentic envi- 

 ronments prevent higher yields, but aeration devices 

 should prove that higher yields are possible. 



Efforts to hand feed largemouth bass have often 

 been discouraging, but work toward this goal con- 

 tinues, and recent reports from the Development 

 Center at Marion, Ala., tell of producing largemouth 

 bass up to 20 cm long by supplemental feeding, with 

 a conversion ratio of 1.4:1. 



Cultural techniques of other species reared at our 

 warmwater hatcheries are described as follows: 



Walleye (Stizostedion vitreum vitreum) 



The walleye is one of our most valuable freshwa- 

 ter sport fish. It also ranks high in the commercial 

 harvest. In reclaimed lakes, that is lakes in which the 

 entire fish population has been deliberately poisoned 

 out, this species has had the greatest success when 

 stocked as fingerlings 5 cm long. 



It has not proved feasible to rear walleyes to 

 maturit) under hatchery conditions. Consequently, 

 adult fish must be trapped from the natural environ- 

 ment during the spring spawning run and hand strip- 

 ped. The eggs are incubated, usually in ajar battery, 

 and the sv\im-up fry stocked into fertilized rearing 

 ponds. Under the best conditions, 5-cm fingerlings 

 are harvested in about 4 wk. 



Muskelliinjje iEsox masquiitongy) and 

 Northern Pike (E. Lucius) 



The muskellunge and northern pike fit a very spe- 



cial niche as efficient predators in shallow lakes. The 

 muskellunge (or muskies for short) is particularly 

 prized as a trophy fish. Both species are reared in a 

 somewhat similar fashion as adult spawners are 

 trapped in the wild and hand stripped. A certain 

 amoimt of success has been achieved in speeding 

 maturation of female northern pike by injecting dried 

 carp pituitary interperitoneally at a rate of 5 mg/kgof 

 body weight. 



Once the eggs have been fertilized and become 

 turgid, they are incubated in jar batteries until hatch- 

 ing and swim-up. The fry are then stocked into fer- 

 tilized ponds and 5-cm fingerlings are harvested 3-5 

 wk later. In the case of muskies, the fingerlings are 

 then stocked back into ponds at a reduced rate and 

 fed forage fish until they reach a length of 25-30 cm. 

 At that size the fish are ready to be stocked back into 

 the natural environment and good survival can be 

 expected. 



In recent years, limited success has been achieved 

 in rearing muskies in concrete tanks on a diet of 

 forage fish. Indications are that there will be more 

 tank culture of this species in the future. 



Bait Fishes 



Bait fishes are raised in farm ponds, natural lakes, 

 and other still waters devoid of predaceous fish. 

 Some of the more common species of bait fish reared 

 in the United States are goldfish, Carassiiis auratiis: 

 golden shiners, Notemigoniis crysoleiicas: and 

 fathead minnows. Pimephales proinelas. Once 

 ponds are prepared, culture in the simplest form may 

 be undertaken by merely introducing adult breeders. 

 The prolific nature of these fish generally results in a 

 rapid increase of the stock by natural reproduction. 

 Annual yields generally range from 1,300 to 4.500 

 kg/ha. 



Channel Catfish, Ictalurus punctatus 



For the past 10 yr channel catfish cultivation has 

 rapidly increased in the United States. There are 

 now approximately 24.600 hectares of ponds de- 

 voted to the growing of catfish. This can be com- 

 pared to 100 hectares 10 yr ago. The gross annual 

 value to the farmers in 1971 was approximately $31 

 million from the 40.800 metric tons produced. 



To date, most catfish rearing has been done in 

 large impoundments, many of them operated in rota- 

 tion with rice farming. More recent entrepreneurs 

 into the catfish farming industry are large corpora- 



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