female; the female was ready and the male 

 possessed no sexual urge . Close observation 

 frequently made easier a decision on the above 

 possibilities. If the female assumed a dominant 

 role and attempted to bite the male, without in- 

 voking a belligerent response from him, we 

 considered the male to be sexually incompetent 

 or in some other way to be incompatible . How - 

 ever, a male thus rejected by the female or by 

 the experimenters could not be classed as a 

 male not ready for spawning, for one such male 

 spawned with a female 4 days later . Any biting 

 on the part of the female, directed either to- 

 wards other females or towards males, was 

 accepted as a sign of readiness to spawn, since 

 paired catfish (both male and female) usually 

 drove other fish away. If the male was not ag- 

 gressive towards a female, some aggressive- 

 ness usually could be evoked by the addition of 

 another male; then we chose the more aggres- 

 sive fish to participate in the subsequent 

 spawning of an injected female. In this situation, 

 however, it was felt that the resident fish had 

 the advantage, but this premise did not always 

 hold true. In one experiment a 21 -inch male, 

 which had previously spawned, was placed with 

 a 17 -inch female. This male exhibited little 

 aggressiveness. He responded by a slight push- 

 ing with his body when other males his size and 

 smaller were added; he assumed what we called 

 an "alert position, " that is, he usually swam or 

 rested slightly off the bottom of the aquarium 

 with some movement expressed in the caudal 

 and pelvic fins, whereas males which did not 

 spawn rested on the bottom with flns drooped. 

 Since this male had previously spawned, he was 

 left with the female, and they later spawned. 



An instance of aggressiveness possibly 

 due only to a disparity in size was also noted. 

 A 16. 1 -inch female, which spawned in an aquar- 

 ium, was placed with a 22 -inch male whose 

 secondary sexual characteristics were not well 

 developed, that is, he possessed a narrow head 

 for his body length, slight gray color on the 

 sides of the jaw, and a papilla that was small, 

 soft, and flabby . A postmortem revealed that 

 the testicular development was poor, and although 

 motile sperm could be obtained by maceration, 

 the testes were no larger than well -developed 

 testes in 16-inch males. This male was overly 

 aggressive towards the female. When the fe- 

 male came to the bottom, the male bit her 



viciously along the top of the caudal peduncle or 

 just behind the pectorals (a favorite target when 

 two males engaged in combat) . Such an attack 

 forced her to swim quickly up and away. Fur- 

 ther attacks by the male sometimes brought her 

 to the bottom, but the male bit her severely at 

 that time, forcing her away again. 



In pairing acts in which aggressiveness 

 occurred, it was observed that if the fish were 

 going to pair, the bites of the male became pro- 

 gressively less severe until they were more like 

 a nudge in the region of the vent, an action that 

 may have led some observers to presume that 

 the male bites a gelatinous plug from the genital 

 orifice (see table 1). In the above-cited case 

 the male was replaced. The male may have been 

 capable of spawning and mlgjit have spawned with 

 a larger female . He may have been too rough 

 for the small female, although some other sim- 

 ilarly matched combinations resulted in successful 

 spawnings . 



No particular behavior which absolutely 

 presaged imminent spawning was noted on the day 

 before spawning. Both fish were active, frequent- 

 ly circling in the aquarium and coming back to 

 rest in the same position, on the bottom of the 

 aquarium , where the eggs were later deposited 

 (see also Fontaine, 1944). 



A few hours before the event, there were 

 some rather positive signs that spawning was to 

 take place . The female occasionally would make 

 what we called "runs" along the bottom . In this 

 type of behavior the female moved over the spot 

 where the eggs were to be deposited in a wiggling 

 motion, the pelvic and pectoral fins alternately 

 beating against the bottom . These run s were 

 short, about 4 to 6 inches . This same behavlof 

 was later a part cf the spawning act and was re- 

 peated many times. As far as our observations 

 indicated, it played two or possibly three roles . 

 These runs of the female, later in the spawning 

 act, aerated the eggs just as the male aerated 

 the eggs after spawning was complete . This 

 motion cleaned the area where the eggs were to 

 be laid. Also it migjit stimulate the male, for, 

 a male would usually attempt to spawn with a 

 female engaged in such behavior . 



The spawning reflex refers to a definite 

 behavior on the pan of the participants . When 



