BREEDING 283 



such essentially fickle phenomena as wind and temperature. 

 Let the wind blow shorewards with abnormal strength and 

 duration, and untold milUons of unhatched Cod may perish, 

 or let the temperature for a few weeks during the summer 

 months be abnormally low, and the same fate may overtake 

 hosts of embryonic Gurnards. Under such conditions it is 

 only by the selection of suitable spawning sites, a prolongation 

 of the spawning dme (on the principle of not putting all the 

 eggs in one basket), and other devices, that the pelagic spawning 

 fishes have held their own." These enormous risks of destruc- 

 tion to which the larval fishes as well as the eggs are subjected, 

 coupled with the difficulty of ensuring that every tgg is ferdhsed 

 after extrusion, have led to the production of huge numbers of 

 eggs by fishes of this type. A single Ling {Molva), 61 inches 

 long and weighing 54 lbs., was found to have 28,361,000 eggs 

 in the ovaries, a Turbot {Rhombus) of 17 lbs. weight more than 

 9,000,000, and a Cod {Gadus), weighing 2ii lbs., 6,652,000; a 

 Flounder {Flesus), however, produces a mere milhon of ova on 

 the average, and a Sole (Solea) only 570,000. So great is the 

 destrucdon of eggs and fry that it has been esdniated that in 

 the case of the Cod less than one egg in every million liberated 

 ever becomes an adult fish. 



The eggs of the Herring {Clupea harengus) are heavier than the 

 sea water and are deposited in sdcky clumps on shingly banks 

 on the sea-floor. They thus escape many of the dangers to 

 which the floadng ova are subjected, but are sdll exposed to 

 the depredadons of hungry fishes of all kinds, and it is a common 

 sight to see hoards of Haddock or other fish following close upon 

 the spawning Herrings, greedily swallowing the newly fertilised 

 eggs. The number of eggs produced by a single female is 

 relatively small as compared with the fishes already mendoned, 

 varying from 21,000 to 47,000. 



Many marine fishes migrate to the quieter and shallower 

 inshore regions to deposit their eggs, and others leave the crowded 

 sea altogether, to seek greater safety for their offspring in the 

 rivers. These anadromous fishes include such well-known forms 

 as the Sea Lamprey {Petmnyzon), Sturgeon [Acipenser), Shad 

 {Alosa), Salmon and Sea Trout [Salmo). Most of them retam 

 the old pelagic habit of leaving the eggs and larvae quite uncared 

 for, and since these are sdll exposed to attacks by predaceous 

 fishes and enemies of all kinds, the ova are produced in large 

 numbers to compensate for the risks to which they are subjected. 

 A mature female Salmon, for example, produces from 800 to 900 



