210 Discussion 



measurable growth. But even in these the regeneration rate rises, 

 and I would suggest that the nitrogen uptake rises too. 



Roiblat: Does this mean that the rate of restoration equals the 

 rate of growth? 



Comfort: The response of regeneration to a growth-promoting 

 stimulus is more sensitive than that of body growth. That is why I 

 would not like to say that regeneration rate is a direct function of 

 growth rate. 



Gerking: Do your findings apply to the male ? 



Comfort: No; the male guppy not only stops growing rather 

 suddenly and early, but also it has tail shapes of different kinds. 

 As far as we have got, in males with small, wild-type tails the per- 

 centage regeneration falls in relation to growth cessation, as in 

 females, but the basic restoration rate always stays higher than in 

 the female. You sometimes find male guppies of all ages which for 

 some reason have not quite completed their growth and which have 

 a very high restoration rate. In strains with big tails, it appears 

 that the rate of restoration is based, as it were, on the wild-type tail, 

 but that anything after that is extra. 



Holt: Dr. Gerking, you have looked at particularly good sets of 

 data and put aside the incomplete oddments. I have had a look at 

 the oddments and have the impression that although no single 

 species shows a statistically significant decline in fecundity (eggs 

 per gram) with increase in size, yet in many cases the points for the 

 larger fish fall below the proportional line. 



Gerking: That is very true. I am not convinced whether the 

 decrease is significant or not. 



Holt: In this kind of study you may be seeing the effects of less 

 fecund fish surviving longer. What we cannot do is to follow a cohort. 

 We need a method of determining the fecundity of live individuals 

 and marking them. 



Rockstein: Was this large longear sunfish that utilized very little 

 protein caught at a great depth, Dr. Gerking ? 



Gerking: No, it was caught in a shallow stream. This observation 

 needs to be confirmed, and I do not wish to over-emphasize that 

 portion of Fig. 1. It may indicate that extremely old fish utilize very 

 little protein for growth. 



Nigrelli: In the experiments carried out in Bermuda on the angel- 

 fish you characterize these fish as herbivores. 



Gerking: We have thought up to this time that they were herbi- 

 vores; it is known that they feed upon algae because algae can be 

 found in the gut. Menzel's experiments (1957), however, indicate 

 that if they are fed exclusively on algae they will not grow, even if 



