138 W. M. GRAHAM—A FISH THAT PREYS ON 
The shady pools frequented by Haplochilus are only a few yards long or broad, 
and are dotted over a large swamp. The water in them is clear, the bottom being 
of mud, decaying leaves and twigs, and when the shade is not too great, they 
contain green reeds and water-plants. On analysis, the water of these pools was 
found to contain only 0°84 grain of chlorine per gallon, though the swamp is little 
more than a mile from the Lagoon. 
As an experiment, some of the fish were placed in a basin of water taken from 
the large water-hole near the swamp, referred to above. This water is of a 
milky opacity, and does not become clear after standing. By analysis the amount 
of chlorine was found to be 0°91 grain per gallon. The water was so opaque 
that the fish could only be seen when close to the surface. Mosquito larve 
introduced into the basin disappeared somewhat more slowly than they did in 
clear water, but they were ultimately all destroyed, and the fish did not appear to 
be injuriously influenced by the change of water. The JHaplochilus were also 
found to flourish in tap-water, so long as they were fed with mosquito larve. 
Fig. 1—Haplochilus grahami, Blgr. x 2. 
The hypothesis therefore seems to me established, that the presence in the 
swamp-pools of these fish effectually prevents the breeding of mosquitos, and the 
question presents itself as to whether they can be employed to produce the same 
result in ponds, water-holes, water-barrels, &c., elsewhere. It should be re- 
membered that these fish have a great capacity for spreading themselves over 
flooded land by leaping from pool to pool. As this part of the country is low- 
lying and frequently flooded, it is probable that if they are not found in a 
particular pool, it is because they cannot live there. Most of the water-holes 
contain cat-fish which would be likely to destroy any small fish introduced, 
especially when, as in this case, they are also conspicuous and defenceless. It 
seems likely, therefore, that it is only in pools free from other fish that the 
