FISHERY BULLETIN: VOL. 73, NO. 4 



Table 1. -Design and results of experiments to test factors suspected of influencing ovulation in the zehrafish. Symbol " + " indicates presence of the 

 factor and symbol "0" indicates absence of the factor. The chi-square values are for comparing results of any experiment with that of the control 

 (experiment 8), and the 0.01 level critical limit is 6.63. 



the experimental chamber for 12 to 18 h in nearly 

 all the trials but for only 4 h in several instances in 

 experiment 2, and then stripped by applying 

 gentle pressure onto the abdomen. The release of 

 ripe ova indicated that the fish had completed 

 ovulation. Failure to give eggs, or the release of 

 immature or ruptured eggs, was considered a 

 negative response. Ripe ova are nearly 

 translucent, round, and about 0.8 mm in diameter 

 before taking on any water, and are not attached 

 to each other. Immature ova are often opaque, may 

 be undersized and irregularly shaped, and are 

 often in clumps. In experiment 8, the female was 

 stripped immediately upon removal from the 

 holding compartment. 



After successful stripping, the female was im- 

 mediately permitted to spawn naturally with a 

 male in order to assure release of all ovulated ova. 

 After approximately 4 to 8 h, the male was 

 removed, and the female was returned to her 

 compartment the following day. Between 

 experiments each female was allowed to rest for 8 

 to 12 days, and males 4 to 6 days. 



After an unsuccessful attempt of stripping 

 eggs, the female was presented with either male 

 pheromone and/or fresh tap water, whatever was 

 lacking originally in the experimental chamber, 

 and then stripped again 4 to 18 h later. If the 

 second stripping failed again, then the female was 

 permitted to spawn naturally with a male. In cases 

 where natural spawning failed, data pertaining to 

 that female were rejected. This procedure assured 

 that an unsuccessful attempt at stripping a female 

 of eggs was due to the subjected treatment and 

 not due to an unripe condition of the female. 



Trials of different experiments were alternated 

 randomly without any definite chronological 

 sequence. 



The experimental chambers in experiments 1, 2, 



5, 6, and 7 were 5-liter all-glass aquaria. In 

 experiment 3, 20-liter aquaria were used and were 

 partitioned into two halves, one the experimental 

 chamber and the other the male chamber. The 

 partitionings were done with 1-mm thick opaque 

 plastic divider perforated with holes 1.5 mm in 

 diameter and 3 mm apart. In experiment 4, a 60- 

 liter aquarium was used and was partitioned with 

 nonperforated black plastic dividers into a 30-liter 

 metabolite chamber, a 15-liter male chamber, and 

 a 15-liter experimental chamber. Water was cir- 

 culated from the metabolite chamber into the male 

 chamber, and then to the experimental chamber 

 and back to the metabolite chamber by means of 

 pumping and siphoning. 



The presence of the male pheromone in 

 experiments 1 and 2 was established by air lifting 

 into the experimental chambers water from a 5- 

 liter aquarium into which a male was introduced 

 simultaneously with the introduction of the 

 female into the experimental chamber, the water 

 then was siphoned back into the male aquarium. In 

 experiments 3 and 4, male pheromone was provid- 

 ed by placing, during the experimental period, a 

 male into the male chamber which was chemically 

 continuous with the experimental chamber 

 because of the perforations or water circulation. 



The presence or absence of temperature shock 

 was established by maintaining the experimental 

 chamber respectively at room temperature (21.0ii 

 1.0°C) or at the temperature of the holding com- 

 partments (27.0 ± 1.0°C). 



The absence of metabolites in experiments 1, 2, 

 3, 5, 6, and 7 was attained by filling the 

 experimental chamber and the male chamber with 

 fresh, dechlorinated tap water. In experiment 4, 

 metabolites were presented by conditioning the 

 system for at least 2 wk with 75 mature zebrafish 

 of both sexes in the metabolite chamber which is 



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