68 MARKETABLE BRITISH MARINE FISHES chap. 



(e\v days or weeks. The period is annual, and occurs at about 

 the same time every year. The total annual crop is shed, and 

 then for the rest of the year no more eggs are laid, but the forma- 

 tion of next season's crop goes on in the roe or ovary. The total 

 number of eggs produced by a single fish is very large, and has 

 been carefully investigated. The method by which this is done is 

 as follows. All the eggs in the roe of a fish, such as a herring, before 

 it has begun to spawn, will be shed in the spawning process, 

 that is to say, all that are large enough to be distinguished with- 

 out a microscope. The whole of the two roes are carefully 

 weighed, and then a small quantity, say |^ oz., is weighed. Then 

 this selected portion of the roe is gradually boiled, in order to 

 separate the eggs and make them more distinct. The number 

 in the selected portion is then counted carefully, and the result 

 is multiplied by the number of times the weight of the selected 

 portion is contained in the weight of the whole of the two roes. 

 For example, suppose the two rocs of a herring weigh 8 oz. or 

 half a pound, and that l- oz. contains i,ooo eggs ; then the total 

 number in the fish is i6,ooo. Dr. T. Wemyss Fulton published 

 in 1890^ the results of an extensive investigation of this kind. 

 Some of his figures will be found in the table opposite. 



It will be seen that in this list the ling is the most prolific 

 and the herring the least, although the herring is a more abundant 

 fish than the ling. This is not so surprising and contradictory 

 as it appears, for the ling is a predaceous fish and very much 

 larger than the herring, and a large predaceous fish must neces- 

 sarily be less numerous than the smaller fishes on which it preys. 

 Next to the ling in fecundity is the turbot, also a large predaceous 

 fish, and next comes the cod. The turbot and plaice may be 

 compared with similar results to those just mentioned in reference 

 to the ling and the herring. The turbot is much less numerous 

 than the plaice, although the latter produces a much smaller 

 number of eggs from each individual fish. 



Such facts as these, which very commonly come before us in 

 the study of the conditions affecting the relative abundance of 

 different animals, show that mere fecundity is by no means the most 

 important condition. If every egg produced byafish developedinto 

 an adult individual the increase in numbers would be very rapid 



1 "The Comparative Fecundity of Sea-Fishes," Ninth Ann. A'i'/>. Fishery Board 

 for Scotland. 



