167 research outputs found
Variation in the food intake of grass carp, Ctenopharyngodon idella (Val.), fed singly or in groups
Each animal may be assumed to possess a unique
combination of physiological traits (Bennett, 1987).
However, there is little information on thc effects of
interindividual variation in fish (Cui and Liu, 1990).
Individual differences in competitive ability, aggressiveness
and or size can lead to the establishment of
dominance hierarchies within groups of fish (Metcalfe,
1989; Metcalfe et al., 1989). The variation in
growth rates in groups of fish are rclated to dominance
hierarchies and preferential access to food
resources by dominant individuals (Jenkins, 1969;
Fausch, 1984; Koebele, 1985). Recently, radiography
has been used to measure individual consumption
rates for groups of salmonids and has demonstrated
considerable inter-individual variation in food intake
(Jobling et al., 1989; Carter et al., 1992a; McCarthy
et al., 1992). Two aims of this study were to use
radiography to examine the variation in the food
consumption rate of grass carp, Ctenopharyngodon
idellu (Val.), held together and to assess whcther variation
in growth rates could bc explained by variation
in consumption rates. A final aim of this study was
to compare the day to day variation in consumption
rates of grass carp held in a group to thosc held
individually, in terms of the individual meal share, in
order to examine the cffect of endogenous influences
on appetite
Swimming physiology of European silver eels (Anguilla anguilla L.): energetic costs and effects on sexual maturation and reproduction
The European eel migrates 5,000–6,000 km to the Sargasso Sea to reproduce. Because they venture into the ocean in a pre-pubertal state and reproduce after swimming for months, a strong interaction between swimming and sexual maturation is expected. Many swimming trials have been performed in 22 swim tunnels to elucidate their performance and the impact on maturation. European eels are able to swim long distances at a cost of 10–12 mg fat/km which is 4–6 times more efficient than salmonids. The total energy costs of reproduction correspond to 67% of the fat stores. During long distance swimming, the body composition stays the same showing that energy consumption calculations cannot be based on fat alone but need to be compensated for protein oxidation. The optimal swimming speed is 0.61–0.67 m s−1, which is ~60% higher than the generally assumed cruise speed of 0.4 m s−1 and implies that female eels may reach the Sargasso Sea within 3.5 months instead of the assumed 6 months. Swimming trials showed lipid deposition and oocyte growth, which are the first steps of sexual maturation. To investigate effects of oceanic migration on maturation, we simulated group-wise migration in a large swim-gutter with seawater. These trials showed suppressed gonadotropin expression and vitellogenesis in females, while in contrast continued sexual maturation was observed in silver males. The induction of lipid deposition in the oocytes and the inhibition of vitellogenesis by swimming in females suggest a natural sequence of events quite different from artificial maturation protocols
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