474
a. B. COWEY AND J. R. SARQENT
Steele and his colleagues (Edwards et al., 1969) appear to reach a
conclusion which is similar, in some respects, from their experiments on
respiratory rate, food intake and metabolism of 0-group plaice at
different temperatures living on natural food. They say “ fish differ
from warm blooded animals in that the efficiency of their conversion
of food should not be considered in terms of food for metabolism plus
food for growth; rather, it appears that increases in food intake are
divided between metabolism and growth. At the lower end of the range
there is some limit to a decreased metabolism but maintenance or
fasting levels cannot be deduced by extrapolation of the relations
between metabolic rate and food supply.” Their hdings however go
beyond the point which we make, and show an actual increase in metabolic rate with increased food intake (metabolic rate a t low feeding
rates being something like 60% of that when unlimited feeding occurs)
so that food conversion efficiency remains more or less constant over a
range of feeding rates. These findings are in marked contrast to those
of the Canadian workers and independent confirmation will be useful.
Edwards et al. (1969) also observed a decline in gross efficiency of
conversion with time, values falling from 36% during the first 30 days
to 10% after 120 days. Later experiments (Edwards et ul., 1970)
showed that this was due to the small size of the containers used.
Fish in larger containers had an average conversion efficiency of 26%
over 103 days. These values exceed those obtained by us when feeding
pelleted empirical rations to young plaice (tank size 107 x 84 x 61 cm)
at 15OC, where conversion efficiencies were between 10% and 15% ; 14
week time periods were used.
The first observations on utilization of natural food by flatfish were
those of Dawes (1930, 1931). The efficiency of utilization of mussel
(Mytilus edulis L.) by plaice varied between individuals and within
the same individual at different times. A feeding rate of between 1%
and 2% body weight per day (of the order of 0-06-0-12 g proteinlday
for a fish of 40 g) served to maintain their initial weight. By and large
fish receiving a restricted ration utilized it better than fish receiving an
excess of food, thus fish receiving twice the aforementioned ration grew
almost as well as fish fed ad lib.
Later Hatanaka et al. (1956a, b) showed with two other flatfish
(Limanda yokohamue Gunther and Kareius bicobratus (Bashilewsky) )
that as the fish increased in size conversion efficiency decreased.
The data of Bowers and Landless (1969) indicate that young turbot
( ~ c ~ ~ h t ~ l m u s
maximus (L.)) utilize the adductor muscle of scallop
(Pecten maximus) with a gross efficiency of 40% (protein e5ciency
ratio 2-4). This is a relatively high priced fish and may be especially
a. B. COWEY AND J. R. SARQENT
Steele and his colleagues (Edwards et al., 1969) appear to reach a
conclusion which is similar, in some respects, from their experiments on
respiratory rate, food intake and metabolism of 0-group plaice at
different temperatures living on natural food. They say “ fish differ
from warm blooded animals in that the efficiency of their conversion
of food should not be considered in terms of food for metabolism plus
food for growth; rather, it appears that increases in food intake are
divided between metabolism and growth. At the lower end of the range
there is some limit to a decreased metabolism but maintenance or
fasting levels cannot be deduced by extrapolation of the relations
between metabolic rate and food supply.” Their hdings however go
beyond the point which we make, and show an actual increase in metabolic rate with increased food intake (metabolic rate a t low feeding
rates being something like 60% of that when unlimited feeding occurs)
so that food conversion efficiency remains more or less constant over a
range of feeding rates. These findings are in marked contrast to those
of the Canadian workers and independent confirmation will be useful.
Edwards et al. (1969) also observed a decline in gross efficiency of
conversion with time, values falling from 36% during the first 30 days
to 10% after 120 days. Later experiments (Edwards et ul., 1970)
showed that this was due to the small size of the containers used.
Fish in larger containers had an average conversion efficiency of 26%
over 103 days. These values exceed those obtained by us when feeding
pelleted empirical rations to young plaice (tank size 107 x 84 x 61 cm)
at 15OC, where conversion efficiencies were between 10% and 15% ; 14
week time periods were used.
The first observations on utilization of natural food by flatfish were
those of Dawes (1930, 1931). The efficiency of utilization of mussel
(Mytilus edulis L.) by plaice varied between individuals and within
the same individual at different times. A feeding rate of between 1%
and 2% body weight per day (of the order of 0-06-0-12 g proteinlday
for a fish of 40 g) served to maintain their initial weight. By and large
fish receiving a restricted ration utilized it better than fish receiving an
excess of food, thus fish receiving twice the aforementioned ration grew
almost as well as fish fed ad lib.
Later Hatanaka et al. (1956a, b) showed with two other flatfish
(Limanda yokohamue Gunther and Kareius bicobratus (Bashilewsky) )
that as the fish increased in size conversion efficiency decreased.
The data of Bowers and Landless (1969) indicate that young turbot
( ~ c ~ ~ h t ~ l m u s
maximus (L.)) utilize the adductor muscle of scallop
(Pecten maximus) with a gross efficiency of 40% (protein e5ciency
ratio 2-4). This is a relatively high priced fish and may be especially