294 



DISCOVERY REPORTS 



Hickling's (1933, pp. 43-4) observations on the very rapidly increasing metabolic strain of spawning 

 among older males of European hake. 



By selecting data from Appendix lie (samples in which five or more fish were weighed, northern 

 and intermediate regions only, and working to mean dates) we can draw curves of the variation 

 in K over the period covered by the observations, for either sex of M. Inibbsi, as shown by the con- 



0700- 



0-650 



30 



40 



50 

 LENGTH IN CMS 



60 



I 

 70 



Fig. 23. Variation of 'average' K with length in male and female Merluccius hubhsi. 



0750- 



0700 



O650 



/ 



^9\ 



I JULY I AUG|SEPT|OCT|N0V| DEC | JAN | FEB | MAR |APR | MAY |JUNE|JULY| AUG|SEPT|oCT | 



Fig. 24. Seasonal variation in the condition factor A' of Merluccius hubbsi, for fish approximating to the 

 mean length of either sex; for further explanation, see text. 



tinuous lines in Fig. 24. Now these curves show a steep fall in the value of K during the summer, 

 which tends to level out towards autumn. This is an almost certain indication that this hake is a summer 

 spawner, as other species of hake elsewhere are known to be. All temperate fishes hitherto studied 

 reach their peak of condition just prior to spawning, and some show very quick recovery from the loss 

 occasioned by that act. Thus the seasonal cycle takes the form of a harmonic curve, and the relative 

 steepness of the left- and right-hand sides of the 'wave' depends («) upon the speed of recovery after 



