pituitaries (Nos. 48, 49), and 2 with 

 buffalofish pituitaries (Nos. 55, 56). All 

 fish received the SEune dosage, 2 milligrams 

 per pound of body weight each 24 hours. 

 One female escaped, but all other fish 

 spawned. One female spawned after 2 injec- 

 tions, 17 after 3 injections, and 1 spawned 

 after 4 injections. 



A study of these data suggest several 

 possibilities: (1) The recipient females 

 were in similar physiological condition and 

 the pituitciries were about equal in potency. 

 (2) The fish were in similar physiological 

 condition and the pituitaries differed in 

 potency, even though all were active enough 

 to produce spawning. (3) The fish differed 

 in physiological condition and the pituitar- 

 ies were equal, and therefore the condition 

 of the female is relatively unimportant. 

 (4) The females were not in similar physio- 

 logical condition, but differences in pitui- 

 tary potencies compensated for differences 

 in the fish. Actually the accumulated data 

 and experience of 3 years' work on channel 

 catfish and other species lead us to believe 

 that the physiological condition of the 

 recipient is more variable than the gonado- 

 tropic activity of the pituitaries of the 

 various donor fish. 



Time of Response 



The interval of time between the last 

 injection and the spawning act varied from 

 2 1/2 hours to 48 hours, with the exception 

 of 1 fish which spawned after 72 hours. 

 However, in the cases of short intervals of 

 response the fish might have spawned without 

 the last injection. Three fish spawned 39 

 hours after a single injection and another 

 spawned 18 hours after 1 injection. Here 

 again the physiological condition of the 

 recipient seemed to be the important factor 

 in early spawning, since the 1-injection 

 fish and the early spawners were usually 

 selected and marked "good" previous to the 

 beginning of the injections. Most of the 

 fish spawned 16 to 24 hours after the last 

 injection. No relation to time of day was 

 evident, as the fish began to spawn at 

 practically all hours. However, more pre- 

 spawning behavior was noted during the 

 hours of darkness, which suggested to us 

 that in future vrork the period of response 

 and number of injections might be reduced 

 by keeping the paired fish in darkness. 

 However, in fish-hatchery practice this 

 technique would be inconvenient, but might 



be of interest from a biological point of 

 view. 



Induced Spawning of Catfish Refractive 

 to Usual Hatchery Procedures 



In 1956 we attempted to induce spawn- 

 ing without pituitary injections in catfish 

 that were collected in 1955 and reared 

 under hatchery conditions. Although these 

 fish appeared to have well-developed gonads, 

 they failed to spawn. No eggs were obtained 

 from 30 pairs stocked in regular hatchery 

 pens, although 3 pairs obtained from the 

 Red River during late May 1956 did spawn 

 within 2 weeks when placed in hatchery pens. 

 Also, only 5 of 30 compairable pairs re- 

 sponded to pituitary injection in aquaria. 

 Now, however, we believe that part of this 

 failure was due to infections which can be 

 reduced by routine use of penicillin. 



Verbal reports from workers in both 

 Arkansas and Nebraska indicate that wild 

 catfish brought into the hatchery do not 

 make good brood fish the first year, where- 

 as fish taken from natural waters shortly 

 before spawning time will usually spawn. 

 Marzolf (1957) reported a similar situation 

 in Missouri and assumed that the wild fish 

 needed a period of 1 to 2 years to become 

 acclimated to pond conditions. By 1957, 

 our brood stock had been in the hatchery 2 

 or more years, and the spawning success in 

 hatchery spawning pens (without pituitary 

 injections) was considerably better than 

 with the same fish in 1956. Of 31 pairs 

 stocked in pens, 22 pairs spawned. The 

 management of this brood stock and the feed- 

 ing was not significantly different from 

 that practiced in 1955-56. 



On June 25, 1957, 8 females were 

 recovered from the outdoor spawning pens 

 and brought into the holding house. These 

 females had been stocked in spawning pens 

 for various lengths of time (10-21 days) 

 but these fish were refractory to the pen 

 treatment and had not spawned, probably 

 because of water temperatures at this time 

 (84° - 86° F.). They were injected with 

 various kinds and combinations of pituitary 

 materials (fish Nos. 21, 42, 47, 50, 51, 

 53, 69, 70; table 2) and all fish eventually 

 spawned. The lowest number of injections 

 was 2, the highest 15. The number of injec- 

 tions required for spawning is not very 

 significant since the fish were used in 

 different experiments and received various 



