balanced energy budget of a carnivorous fish based on published data for 15 species of fish; 100I = 44 9 7M + 29 9 6G + 27 9 3E Brett and Groves, 1979.
The total metabolism can be further broken down into standard metabolism M
S
, feeding metabolism M
F
, active metabolism M
A
including swimming, and the heat increment, or energy of specific dynamic action SDA Fig. 1. The above
numeric model was used to reflect the change in growth due to a change in energy expenditure due to swimming. For example, if a species used 10 instead of 6.75
of its available energy for swimming, then according to Fig. 1 the energy available for growth would decrease from 29 of total energy to 25.75.
3. Results
3
.
1
. Shape When both species were examined together, some interesting trends became
evident. For fish of the same mass, Atlantic salmon were longer than chinook salmon, but chinook salmon were both taller and had a larger girth than Atlantic
salmon of the same weight Figs. 2 – 4. The slopes of the regression lines for the
Fig. 1. The energy budget of 3 kg-sized Atlantic and chinook salmon. The values within the boxes are in units of kcal kg fish
− 1
day
− 1
; values beside the arrows are percentages. The circled lettering corresponds to that of the energy budget discussed in the text. Where two values are given, the first one
is for Atlantic salmon and the figure in parentheses is for chinook salmon. Note that the increase in activity for chinook salmon as compared to Atlantic salmon from 23 to 24.35 results in an increase
in metabolic costs and a corresponding decrease in growth modified from Brett and Groves, 1979.
Fig. 2. Atlantic salmon are longer than chinook salmon of the same weight for clarity, only a subset of available data is presented, n = 298 Atlantic salmon and 146 chinook salmon. Slopes in the regression
equations relating mass, M, to length, L, were significantly different.
Fig. 3. The girth of an Atlantic salmon is smaller than the girth of a chinook salmon of comparable weight n = 298 Atlantic salmon and 146 chinook salmon. The y constants in the regression equations
relating mass, M, to girth, G, were significantly different.
transformed variables of length and weight, and height and weight for the two species were significantly different differences of the y-intercepts were not tested,
but was not significantly different for girth and weight. The y-intercepts for the regression lines for girth and weight were, however, significantly different.
A roundness of one would indicate that the fish had a perfectly round cross section. The average roundness of chinook salmon 0.837 was not significantly
different from that of Atlantic salmon 0.836 Fig. 5, and indicated that both
fishes tended to have elliptically shaped cross sections height \ thickness. Round- ness did not correlate to fish weight. It can be ascertained from these results
roundness, height and girth that the thickness of a chinook salmon is greater than the thickness of an Atlantic salmon of similar weight.
Fig. 4. The height of an Atlantic salmon is smaller than the height of a chinook salmon of comparable weight n = 298 Atlantic salmon and 146 chinook salmon. The slopes in the regression equations
relating mass, M, to height, H, were significantly different.
Fig. 5. No significant difference exists between the roundness of the cross-sections of Atlantic and chinook salmon n = 298 Atlantic salmon and 146 chinook salmon.
Fig. 6. The average swimming speed of farmed salmon was 0.68 m s
− 1
. Each point represents the average speed found at a camera position in a cage. The standard deviation at each position for chinook
salmon was 9 30 – 40 of the value, while it was only 9 7 for Atlantic salmon. All data came from low current velocity salmon farming sites.
3
.
2
. Swimming speed As a general observation, the variation in swimming speed at any camera
position was significantly higher for chinook 9 30 – 40 of the average positional speed than for Altantic salmon 9 7 of the average positional speed. From the
video footage, chinook salmon exhibited far more darting, acceleration and direc- tional changes than Atlantic salmon; in other words, they seemed ‘wilder’ and
responded much more readily to outside stimuli, while the Atlantic salmon behaved in a more domesticated fashion. Swimming for all positions and species was
quasi-steady; fish coasted between bouts of acceleration.
After averaging together all the positional swimming speeds, the overall average swimming speeds for both species were 0.68 m s
− 1
not significantly different. The swimming speed obtained at each camera position did not correlate with the mean
positional fish weight Fig. 6, water temperature or time of day for details on temperature and time of day, see Jones, 1997. Water temperature varied depending
on the time of year between 7 and 14°C.
3
.
3
. Drag and power Both drag and power Fig. 7 increased as individual fish weight increased. For
Atlantic salmon, power requirements tended to level off after a fish reached 3.5 kg in size. A visual comparison of the curves for each species showed that the power
requirement of a 2 – 4 kg chinook salmon was 20 higher than the power requirements for Atlantic salmon of the same weight. A 4-kg chinook salmon used
25 more energy to swim than an Atlantic salmon of similar size.
When comparing how the two species use available energy, some interesting trends became evident Fig. 8. The curve representing the distance different sizes of
fish could move on 1 W s of energy was hyperbolic. This trend is more easily seen for Atlantic salmon, as a wider range of data were available for Atlantic salmon
than chinook salmon. The inflection point on the curve occurred between 1 and 1.5 kg of weight. Fish smaller than 1 – 1.5 kg moved a much greater distance per 1 W
s of available energy than larger fish.
The curve representing how much weight a fish could move per 1 W s of available energy was also non-linear Fig. 8. For both species, as fish increased in
weight they became more efficient carriers of weight. The chinook salmon was always less efficient as it could carry less weight given the same amount of available
energy than an Atlantic salmon of similar size. An inflection point occurred in the curve at an approximate weight of 1.25 kg for Atlantic salmon as before,
insufficient data were available for chinook salmon. Therefore, after 1.25 kg, fish changed from being efficient long distance travelers to efficient carriers of weight
Fig. 8.
3
.
4
. Effect on growth The energy requirement due to swimming varied as the fish grew, increasing from
2 of the total energy supplied for a 1 kg fish to 6.7 for a 3 kg Atlantic salmon Figure not shown, as the shape is similar to Fig. 7. The energy requirement due
to swimming for a chinook salmon was 20 higher throughout the same time interval. This increased cost of swimming for chinook salmon decreases the amount
of energy available for growth by 4.5 day
− 1
4.5 = 10029 − 27.729 see Fig. 1.
Fig. 7. Power requirements for swimming by salmonids increased as the fish grew. For Atlantic salmon, the power requirements tended to level off when the fish reached a weight of 3 kg.
Fig. 8. Utilization of available energy for swimming: 1 Atlantic salmon; 2 chinook salmon. For Atlantic salmon the shape of the two curves had an inflection point at 1.25 kg. Prior to that size, fish
could travel further on a unit of energy, while after that size, fish could carry more weight per unit of energy.
4. Discussion
