the injected fish spawned successfully. The 

 time of day when spawning occurred may have 

 been influenced by the time of the last injection, 

 and may not have been indicative of the normal 

 spawning hour . The duration of the spawning 

 act, the frequency of egg emission, and the in- 

 tensity of spawning activity might have been 

 dependent upon the dosage and schedule of in- 

 jections . Since our data concur with the indirect 

 description c£ the spawning of a noninjected pair 

 of channel catfish (Fontaine 1944) and since we 

 have observed the behavior of several other 

 species which were induced to spawn by the 

 pituitary method, we do not believe that the 

 basic spawning pattern was modified by the pitu- 

 itary injections. Rather, any visual, physical, 

 or chemical stimuli which normally cause the 

 fish's own pituitary to secrete the gonadotropins 

 necessary to precipitate the spawning act were 

 byjjassed, so to speak, by the exogenous gonad- 

 otropins . 



papilla was resilient and recovered its original 

 shape after being rubbed in a posterior to anter- 

 ior direction, a test which we frequently used. 

 Both gross and microscopic examination of the 

 testes have verified the value of this test for the 

 papilla, since males with small, soft genitals 

 had underdeveloped testes, whereas a fish with 

 a relatively firm papilla possessed correspond- 

 ingly better developed testes . 



The males were not injected with pituitary 

 materials . Two males received androgens 

 (testosterone) several days before they were 

 spawned, but no information was obtained to in- 

 dicate whether the injections influenced spawning. 

 One male had spawned previously outside in the 

 regular hatchery spawning pens . Another male 

 spawned with two females in the aquarium experi- 

 ments and tended the eggs of a third spawning. 



PRESPAWNING BEHAVIOR 



SELECTION OF FISH FOR SPAWNING 



Fish for spawning were selected during 

 the breeding season, from the middle of April 

 to the last week in July when water temperatures 

 ranged from 70° to 85° F. According to oral 

 reports from the Federal fish-culturists of the 

 southwestern United States, the largest or old- 

 est fish spawn first, while the smallest fish are 

 usually the last to spawn. 



Each selected female was placed with a 

 male in an aquarium . The condition of the 

 females for spawning was rated excellent, al- 

 though it was always difficult to evaluate the 

 exact physiological condition . Each female was 

 well-rounded, and the roundness of the abdomen 

 extended past the pelvics to the genital orifice. 

 The belly was flaccid, and the genitals were 

 raised and reddish. The females ranged from 

 14 to 17 inches in length. They received pituitary 

 injections to induce spawning. 



On the basis of external characters, the 

 males also were judged to be in excellent spawn- 

 ing condition. They were from 15 to 21 inches 

 long and each possessed good secondary sexual 

 characteristics- -a head slightly wider than the 

 body, pigmented jaw and belly, and distinct, 

 well -formed genital papilla, with the opening of 

 the urogenital duct somewhat dilated. The 



When males and females (either Injected 

 or noninjected) were placed together in an aquar- 

 ium there were various reactions and responses 

 on the part of the male, which may be generally 

 classified as aggressive or passive. If he was 

 aggressive, he bit and drove the female; and 

 this behavior usually continued for 20 or 30 min- 

 utes, or occasionally until the female was near 

 the point of death. This aggressiveness usually 

 stopped if the female remained in a given loca- 

 tion near the bottom of the aquarium . If she 

 assumed this position and the two stayed beside 

 one another and/or frequently swam in circles, 

 we considered the participants paired. If the 

 female swam off too far the male hazed her again 

 until she returned to her original position . If 

 the female persistently swam up from the bottom, 

 the aggressive male pursued her with such vigor 

 that it was not long before she was exhausted or 

 injured, and swam along the sides of the aquarium 

 at the top of the water. This action was taken to 

 mean the female was not ready for pairing, and 

 she was removed. 



If the male was passive to the female, 

 then a number of possibilities existed: the male 

 and female were not ready for spawning, and 

 therefore did not mutually stimulate each other 

 to sexual display; both were ready and pairing 

 was spontaneous without benefit of courtship; or 

 the male was ready and willing to accept any 



