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Evidence for the absence of an endogenous growth-rate rhythm in brown trout (salmo trutta linn.)
Comp. Biochem. Physiol., 1962, Vol. 6, pp. 91 to 93. Pergamon Press Ltd., London. Printed in Great Britain
SHORT COMMUNICATION EVIDENCE FOR T H E ABSENCE OF AN E N D O G E N O U S GROWTH-RATE RHYTHM IN BROWN T R O U T (SALMO TRUTTA LINN.) D. R. S W I F T Freshwater Biological Association, Windermere, England
(Received 30 January 1962) Abstract--Experimental evidence is presented showing that brown trout kept in a constant environment do not show an endogenous growth-rate rhythm.
INTRODUCTION BROWN (1946) presented evidence to show that brown trout grew in a regular rhythmical fashion while living in a constant environment. There was "an autumn check, a spring maximum, rapid summer growth and another autumn check". Such a rhythm would be of obvious importance in the control of the annual growth-rate cycle demonstrated to occur in these animals (Swift, 1961). In view of the reasons (Swift, 1961) for thinking this evidence insufficient, further experimental data were sought on the growth-rate of brown trout living in a constant environment. METHODS Previous results showed that it would be difficult to keep sufficient fish under experimental conditions to allow of any statistical treatment of the results (Brown, 1946; Swift, 1961). Single 1-year-old fish were therefore used for this work, each fish being kept in one half of a constant environment aquarium (Swift, 1961). The fish, kept separately in order to eliminate any possible effect of competition, were fed to satiation on minced liver (Swift, 1960). Under these conditions any consistent endogenous rhythm could be expected to show in the growth of each individual fish. Two fish were kept at each of a series of temperatures (5 °, 8 °, 1 0 ° and 12°C) selected to culminate at the optimum temperature for growth (Swift, 1961). The fish were introduced into the tanks in October 1960, and the experiments started in December and lasted until September 1961. At interval, the fish, anaesthetized with tricaine-methanosulphonate, were weighed and measured. 91
92
D.R. SwlvT RESULTS AND I)ISCUSSION
The growth-rate of the fish were calculated according to the specific growthrate formula previously used (Swift, 1961) and the results, expressed as the percentage increase per week, are shown in Fig. 1. Each fish grew at a different rate at different times of the year, but no two fish showed contemporaneous variations in their growth-rate. •
e~o
e ~ e ~
I --
J I
Meon
0 ~,~ 2 - -
IO°C
l
c
i
q
•
I
•
i
5 c
Q
~
O
•
D 1= o
u u c,3
8 °C
12°C I Dec
l Feb
L Apr
, June
I Jl,~.
SeW
FIe;. 1. The specific growth-rate, .lnL=-lnLt . . . v.. 100, expressed as the perT2- T1 centage increase in length per week of the individual fish over the time of the experiment. The means of the growth-rates are shown. "In a constant environment, growth proceeds with uniform specific velocity" (Medawar, 1945). The same author pointed out that as the internal environment of complex organisms cannot be kept constant experimentally only tissue cultures
ABSENCE OF AN ENDOGENOUS GROWTH-RATE RHYTHM IN BROWN TROUT
93
and non-cellular organisms can be induced to grow logarithmically for any significant length of time. The mean of each series of observations is shown; this mean is nearly constant throughout the experiment. It is not surprising that the growth-rate of the individual fish varied over the time of the observations; however, these variations in no way indicated the influence of an endogenous growth-rate rhythm. One further point may perhaps be noted from these results; the fish living at the different temperatures of the experiment all tended over the period of observation to a common growth-rate of 1 per cent/week. T h s is most apparent in those fish growing at 5°C whose growth-rate steadily increased, suggesting that the fish adapted to their environment in such a fashion that their mean growth-rate tends to a level independent of the environmental temperature. REFERENCES BROWN M. E. (1946) The growth of brown trout (Salmo trutta Linn.)--II. The growth of two year old trout at a constant temperature of 11"5°C. J. Exp. Biol. 22, 130-144. MEI)AW~a P. B. (1945) Essays on Growth and Form. Clarendon Press, Oxford. SWIFT D. R. (1960) An improved feed for experimental fish. Nature, Lond. 187, 1133. SWXFTD. R. (1961) The annual growth-rate cycle in brown trout (Salmo trutta Lirm.) and its cause. J. Exp. Biol. 38, 595-604.
SHORT COMMUNICATION EVIDENCE FOR T H E ABSENCE OF AN E N D O G E N O U S GROWTH-RATE RHYTHM IN BROWN T R O U T (SALMO TRUTTA LINN.) D. R. S W I F T Freshwater Biological Association, Windermere, England
(Received 30 January 1962) Abstract--Experimental evidence is presented showing that brown trout kept in a constant environment do not show an endogenous growth-rate rhythm.
INTRODUCTION BROWN (1946) presented evidence to show that brown trout grew in a regular rhythmical fashion while living in a constant environment. There was "an autumn check, a spring maximum, rapid summer growth and another autumn check". Such a rhythm would be of obvious importance in the control of the annual growth-rate cycle demonstrated to occur in these animals (Swift, 1961). In view of the reasons (Swift, 1961) for thinking this evidence insufficient, further experimental data were sought on the growth-rate of brown trout living in a constant environment. METHODS Previous results showed that it would be difficult to keep sufficient fish under experimental conditions to allow of any statistical treatment of the results (Brown, 1946; Swift, 1961). Single 1-year-old fish were therefore used for this work, each fish being kept in one half of a constant environment aquarium (Swift, 1961). The fish, kept separately in order to eliminate any possible effect of competition, were fed to satiation on minced liver (Swift, 1960). Under these conditions any consistent endogenous rhythm could be expected to show in the growth of each individual fish. Two fish were kept at each of a series of temperatures (5 °, 8 °, 1 0 ° and 12°C) selected to culminate at the optimum temperature for growth (Swift, 1961). The fish were introduced into the tanks in October 1960, and the experiments started in December and lasted until September 1961. At interval, the fish, anaesthetized with tricaine-methanosulphonate, were weighed and measured. 91
92
D.R. SwlvT RESULTS AND I)ISCUSSION
The growth-rate of the fish were calculated according to the specific growthrate formula previously used (Swift, 1961) and the results, expressed as the percentage increase per week, are shown in Fig. 1. Each fish grew at a different rate at different times of the year, but no two fish showed contemporaneous variations in their growth-rate. •
e~o
e ~ e ~
I --
J I
Meon
0 ~,~ 2 - -
IO°C
l
c
i
q
•
I
•
i
5 c
Q
~
O
•
D 1= o
u u c,3
8 °C
12°C I Dec
l Feb
L Apr
, June
I Jl,~.
SeW
FIe;. 1. The specific growth-rate, .lnL=-lnLt . . . v.. 100, expressed as the perT2- T1 centage increase in length per week of the individual fish over the time of the experiment. The means of the growth-rates are shown. "In a constant environment, growth proceeds with uniform specific velocity" (Medawar, 1945). The same author pointed out that as the internal environment of complex organisms cannot be kept constant experimentally only tissue cultures
ABSENCE OF AN ENDOGENOUS GROWTH-RATE RHYTHM IN BROWN TROUT
93
and non-cellular organisms can be induced to grow logarithmically for any significant length of time. The mean of each series of observations is shown; this mean is nearly constant throughout the experiment. It is not surprising that the growth-rate of the individual fish varied over the time of the observations; however, these variations in no way indicated the influence of an endogenous growth-rate rhythm. One further point may perhaps be noted from these results; the fish living at the different temperatures of the experiment all tended over the period of observation to a common growth-rate of 1 per cent/week. T h s is most apparent in those fish growing at 5°C whose growth-rate steadily increased, suggesting that the fish adapted to their environment in such a fashion that their mean growth-rate tends to a level independent of the environmental temperature. REFERENCES BROWN M. E. (1946) The growth of brown trout (Salmo trutta Linn.)--II. The growth of two year old trout at a constant temperature of 11"5°C. J. Exp. Biol. 22, 130-144. MEI)AW~a P. B. (1945) Essays on Growth and Form. Clarendon Press, Oxford. SWIFT D. R. (1960) An improved feed for experimental fish. Nature, Lond. 187, 1133. SWXFTD. R. (1961) The annual growth-rate cycle in brown trout (Salmo trutta Lirm.) and its cause. J. Exp. Biol. 38, 595-604.