842 BULLETIN OF THE BUREAU OF FISHERIES. 



THE LARV/E OF FLIES. 



The experiments at Craig Brook have included a considerable list of insects 

 and Crustacea, but the most attention has been given to the larvae of flies, espe- 

 cially of two species of flesh fly, the bluebottle fly {Calliphora erythrocephalon) 

 and the green flesh fly {Lucilia ccesar) . During some eight years this work was 

 made especially prominent and on a scale sometimes equivalent to the feeding 

 of as many as 100,000 fingerlings wholly on this food. In most cases there was a 

 mixed ration of fly larvae and chopped meat, but the exclusive use of the larvae 

 here and there affords data for definite and accurate statements of the compara- 

 tive influence of the two regimens on the rate of growth, which is as far as data 

 now available enable us to go. 



The methods of the work may be thus briefly described: 

 Some kind of fresh animal matter, mainly slaughterhouse refuse and such 

 parts of animals slaughtered or dressed at the station as were not available for 

 direct feeding, were exposed to the visits of the flies, and, when well stocked 

 with eggs, placed under the shelter of a building protected as far as practicable 

 from marauding insects, such as carrion beetles, in specially constructed boxes, 

 in which the larva; assembled themselves when fully grown in masses conven- 

 iently handled. These were fed to the fish in troughs or ponds, mainly in 

 wooden troughs about 10 feet long and i foot wide, sometimes in conjunction 

 with other articles and sometimes alone, but in the latter case the fry had gone 

 through a preparatory stage of feeding on chopped liver or similar meat for a 

 few weeks, during which they had attained sufficient size to swallow young 

 larvae. The fry generally began to take food about June i. The feeding of 

 larvEe was generally begun early in July and was continued till some date in 

 October, when the fish were counted, weighed, and liberated. The weighing 

 was done in this way: A pail of water was suspended from a spring scale and 

 its weight accurately noted. Then 200 fish or less by count were held in a soft 

 net until the water had drained from them, when they were turned into the pail 

 of water and the increase in weight noted. In case of very small numbers, each 

 fish was weighed separately on a very delicate balance. The record is therefore 

 very accurate. Sometimes the larvae were given alternately with chopped 

 meat, and in many other cases there were changes sufficient to forbid deductions 

 as to the influence of the food on the growth of the fish, but here and there are 

 cases giving positive evidence of importance. 



In 1888 the record shows that lots no. 10 and 11 were fed through the 

 season exclusively on chopped meat of various kinds (almost wholly butcher's 

 offal), and lot no. 13 was fed on larvae exclusively after June 2. In detail the 

 treatment of the several lots was as follows: 



