20 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



lias this year attained much more encouraging results, having hatched 

 in some cases over 80 per cent of the eggs placed in the McDonald 

 cod apparatus. 



SUMMARY AND CONCLUSIONS. 



Following is a brief summary of what seem to be the most important 

 results of the summer's work, but I wish particularly to point out that 

 the statements contained in this report, based upon the limited data of 

 but one season's experience, have not the force of final conclusions, but 

 are offered as suggestions only, which 1 hope may be useful to the next 

 student who takes up the problem of mackerel propagation : 



During the season of 1897 the common mackerel spawned only very 

 sparingly within the limits of Casco Bay, but in greater numbers at 

 some unknown distance off the coast. Those fish which entered Casco 

 Bay after July 1 were in mixed schools, but most of the females were 

 already spent, or partly so. The best run of spawning fish occurred in 

 this region, according to the united testimony of the fishermen, during 

 the first half of June. 



For each individual mackerel the season of productiveness extends 

 over several weeks, the eggs being produced iu several batches, which 

 mature in succession. Night spawning is probably the rule with the 

 mackerel, but the eggs probably continue to be dehisced into the ovarian 

 cavity during most of the day. I have collected an abundance of 

 evidence bearing on this point. 



There are indications that eggs produced by mackerel in different 

 regions differ in size. This may result from the existence of quite dif- 

 ferent schools or races. During the course of its development the egg 

 increases in specific gravity, owing to absorption of the oil-drop, and 

 sinks beneath the surface, where it encounters higher densities and 

 other changed conditions. 



The morphology of development does not differ in essentials from 

 that of the cod, Spanish mackerel, and sea bass, which has been well 

 described in publications of the United States Fish Commission. Irreg- 

 ularities of segmentation occur with unusual frequency and at unusu- 

 ally early stages. 



The eggs collected from trap nets in the latter part of the afternoon, 

 though sometimes presenting evidence of being not quite mature, were 

 very easily fertilized and seemed to be healthy. 



Fertilization should be effected by the wet method and immediately, 

 as the sperm retains its vitality for a short time only. 



The fertilized eggs are best transported in vessels of water ; cheese- 

 cloth and muslin trays have proved unsatisfactory. The eggs should 

 be freed of surplus sperm and be prevented from overheating. 



The indications are that the poor results attained on the Fish HawJc 

 are due not so much to the poor quality of the eggs as to some defect 

 in the apparatus, possibly to some deleterious substance introduced 

 somewhere in the hydraulic system. 



