394 Phylum Arthropoda 



the limiting factor of production was perhaps insufficient or improper 

 food or the chemical composition of the water. 



The highest rate of production was obtained under these controlled 

 spawning conditions. This method, however, has the disadvantage of 

 being the most expensive of the three. The breeding cage described 

 cost $91.11, but this amount could be greatly reduced by reducing the 

 height of the cage. After the cage was built it was discovered that it was 

 twice as high as was necessary, since the adults will mate in a very small 

 enclosure. 



Natural spawning. This method of propagation differs from the 

 preceding in that the ponds used for rearing the larvae were not screened 

 in and were stocked with eggs by the natural supply of midges attracted 

 to them. Under such conditions it was, of course, impossible to limit the 

 stocking to a single species. "Blood worms" of several species occurred 

 in these cultures; the predominant ones were Chironomus tentans, C. 

 cayugae, and C. cristatus, enumerated in the order of abundance. 



The natural spawning method requires less labor and time, and does 

 not necessitate the expense of a screen cover. On the other hand, the 

 rate of production is considerably lower than that of the other two 

 methods. The results obtained, however, and the fact that the method 

 is very simple in operation and practical in application, seem to justify 

 its use. 



Natural spawning supplemented. In this method the natural supply 

 of eggs deposited by wild breeders was supplemented with eggs taken 

 from the breeding cage. The procedure in operating these ponds was to 

 fertilize them as before and then, two days later, to stock them with a 

 supply of midge eggs from the breeding cage. The eggs were collected 

 with a small dip net and transferred to a pan of water in which they 

 were carried to the ponds or troughs to be stocked. 



The natural spawning method supplemented by eggs from breeders 

 reared in captivity has also a high rate of production, but here again a 

 breeding cage must be maintained. However, the rearing pond does not 

 need to be screened in, and therefore the expense is not nearly so great 

 as for controlled spawning. The breeding cage used in this investigation 

 supplied an average of 94 egg masses per day over a period of 6 weeks, 

 and this number of eggs is sufficient for supplementing six or eight 

 8x12 ft. ponds. Therefore, a single cage properly operated will support 

 a number of ponds. One can collect 100 egg masses in 30 minutes if the 

 water in the ponds is not deeper than 4-5 inches. 



Of the fertilizers which have been tried, soybean meal gave the best 

 production ; sheep manure plus soybean meal gave the second best ; and 

 the combination of sheep manure and superphosphate gave the poorest. 

 Soybean meal alone is less expensive than the other two combinations. 



