Abstract
The growth and metabolic responses of rainbow trout to salinities of 10, 20 and 28 ppt and freshwater were investigated under varied dietary conditions.During the spring and summer, voluntary food consumption was greatest in 10 and 20 ppt and least in 28 ppt. During the winter, salinity had no effect on this parameter.
Energy balance studies showed that total metabolic rates increased directly with feeding rate. Metabolic rates were least in 10 ppt, equal in freshwater and 20 ppt and greatest in 28 ppt.
Growth, as calories retained, was optimal at 10 ppt, equal at 20 ppt and freshwater and least at 28 ppt.
Salinity did not influence the proximate body composition of trout.
No change in apparent digestibility was elicited by salinity except at 28 ppt where lower values were found.
Apparent SDA was unaffected by salinity but increased as feeding rate increased.
Feeding trials snowed that specific growth rates and gross growth efficiencies were higher in 10 ppt than freshwater and 20 ppt at six different feeding rates. Maintenance ration levels were least in 10 ppt.
While an increase in feeding rate caused a proportional decrease in net growth efficiencies, no effect of salinity on this parameter was observed.
Nitrogen balance studies showed that salinity caused small changes in apparent and true protein digestibilities at different levels of protein intake.
Total nitrogen excretion was lower in 10 ppt than freshwater and 20 ppt at different protein intakes as was endogenous nitrogen excretion.
Nitrogen retention was optimal in 10 ppt while maintenance protein requirements were least in this salinity.
Salinity produced no marked effect in NPU values.
It was concluded that the changes in both metabolic rate and maintenance energy/nitrogen requirements elicited by seawater resulted from an alteration of the energy requirements for osmotic and ionic regulation.
| Date of Award | Aug 1976 |
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| Original language | English |
| Awarding Institution |
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Keywords
- salmonids
- energy balance
- nitrogen balance
- salinity
- osmotic regulation
- ionic regulation
- salmonid metabolism