FISHERY BULLETIN. VOL. 69, NO. I 



worms {Enchytraeus albidzis' and Tubifex sp.), 

 two species of crustaceans (Daphnia and Cy- 

 clops), beef liver, fresh lettuce, spinach, and 

 several brands of commercial fish food. 



The fish were subjected to a daily 16-hr light 

 and 8-hr dark cycle. The lighting used was a 

 combination of daylight fluorescent bulbs and 

 mercury vapor arc lamps. Most fish were ready 

 to spawn under these conditions within 3 weeks 

 of capture, although there was marked seasonal 

 and individual variation. Observations made 

 suggest the length of the light period is more 

 important than light intensity for the induction 

 of spawning. Kinne and Kinne (1962) reported 

 using a 14L-10D cycle with a combination of 

 fluorescent tubes and natural daylight. 



SPAWNING METHODS 



The fish were spawned on a varied schedule, 

 depending on the readiness of the female. The 

 average female spawned 50 to 200 eggs, de- 

 pending upon her size, approximately once a 

 week. One large, exceptionally prolific female 

 spawned 200 eggs twice a week for 2 months. 

 Subsequently, this female was not spawned on 

 schedule, became eggbound, and was unable to 

 extrude her eggs. After her death the large, 

 single ovary contained over 800 eggs and ac- 

 counted for 44 ""r of the total body weight. Fe- 

 males that would not spawn at room temperature 

 were spawned at 27° C. Females that could 

 not spawn at either room temperature or 27° C 

 were removed from isolation to a community 

 tank (4 females, 2 males) on a 12L-12D photo- 

 period, wherein they quickly spawned out their 

 eggs at 27° C. Kinne (1960) reported that the 

 fish do not spawn in the laboratory at temper- 

 atures below 20° C and seem to spawn optimally 

 between 28° and 32° C. He also noted that 

 the temperature in the field varies betw-een 25° 

 and 35° C for most of the spawning season. 



Kinne and Kinne (1962) reported that i)up- 

 fish embryos have one period of low thermal 

 stability between fertilization and gastrulation 

 and a second period just before hatching. Ob- 



' See Kinne (1960) for details on mass culturinK 

 Enchytraeus albidus. 



sei-vations made during our study indicate an- 

 other period of low thermal stability just before 

 fertilization. When a female maintained at 

 room temperature is transferred to a higher tem- 

 perature to induce spawTiing, most of the eggs 

 either are not fertilized or do not develop. We 

 found that females should be maintained and 

 spawned at one temperature. If maintained at 

 a temperature above 25° C, they will need to 

 be spawned regularly; otherwise, the eggs are 

 dropped to the bottom of the aquarium un- 

 fertilized. A more flexible spawning schedule 

 is possible if the female is kept at a lower tem- 

 perature. 



The fish were spawned in white, plastic, food 

 containers measuring 27 x 20 x 10 cm, con- 

 taining 2.5 liters of water at 22° C. Immedi- 

 ately after the spawning these containers were 

 suspended in a water bath at 27° C. This tech- 

 nique produced good hatches in spite of the re- 

 ported low thermal stability bet^veen fertiliza- 

 tion and gastrulation (Kinne and Kinne, 1962). 

 The water bath was a 20-gal tank with a stand- 

 ard aquarium heater. 



Either a green plastic mat or white cheese- 

 cloth was used as a substrate on which the fe- 

 males could attach the adhesive eggs. On several 

 occasions, when the plastic mat was used, the 

 pupfish were observed eating the previously 

 spawned eggs, which were readily visible against 

 the green background. The substitution of 

 cheesecloth with L-shaped glass-rod weights at 

 its periphery successfully reduced parental egg 

 consumption. The cheesecloth was a superior 

 substrate because many of the eggs were buried 

 in the material and thus were inaccessible to 

 the parents. Furthermore, the combination of 

 a white spawning bin, white cheesecloth, and 

 nearly transparent eggs made the latter virtually 

 invisible to the experimenters and, presumably, 

 to the fish. 



The parent fish were well fed prior to spawn- 

 ing to help reduce the number of eggs consumed. 

 The spawning bin, containing the female, was 

 placed in a quiet location. Five to fifteen min 

 later the male was introduced to the spawning 

 bin which was then left undisturbed for 1 to 

 2 hr. Barlow (1961) reported that spawning 



154 



