Physiology of Finfish and Shellfish (2+1)

4.4.1. Introduction

Animals need chemical energy to carry out their various functions and their overall use of chemical energy is often referred to as their energy metabolism.

Animals obtain energy mostly through the oxidation of food stuffs and their consumption of oxygen can therefore be used as measure of their energy metabolism. Some animals can live in the absence of free oxygen; they still utilize chemical energy for their energy needs, although the metabolic pathways are different. Such animals meet their energy needs through anaerobic metabolism. This situation is normal for quite a few animals that live in oxygen-poor environments and/or tolerate prolonged exposure to lack of oxygen.

The energy-requiring processes and reactions in the living organism use a common source of energy, adenosine triphosphate (ATP). This ubiquitous compound, through the hydrolysis of an “energy-rich” phosphate bond, seems to be the immediate source of chemical energy for processes such as muscle contraction, ciliary movement, firefly luminescence, discharge of electric fish, cellular transport processes, all sorts of synthetic reaction and so on. ATP is formed at the various energy-yielding steps in the oxidation of foodstuffs and also in anaerobic energy-yielding process, but in smaller amounts. ATP is a universal intermediate in the flow of the chemical energy of the food to the energy-requiring process of metabolism in both aerobic and anaerobic organisms.

• Energy utilization in fish
• Rate of energy expenditure, the losses and gains and efficiency of energy transformation as functional relation to whole organism bio energetic.
• Ecological energetic: organism to its environment and trophic level.
  

Energy metabolism difference from that of on animals and birds by two aspects:

1. Fish don’t expand energy to maintain the body temperature different from that of their environment.
2. The excretion of waste nitrogen requires less energy in fish than it does in homeothemoric land animals.
   

Metabolism = Anabolism + Catabolism

↓ ↓ Activity increase

Growth Negative growth

The energy conversion involved in biological system is studied either by direct calorimeter or indirect calorimeter. The direct calorimeter has been considered unsatisfactory for studies on fish because of the con heat production by fish and the higher heat capacity of the water in the system. Indirect calorimetry involves measurement of gas exchange, the calorific equivalents for oxygen uptake and carbon-di oxide production based on heats on combustion of different energy substances. The type of physiological fuel involved can be established by determining the respiratory quotient (RQ) and the urinary or non-faucal nitrogen. Under totally aerobic condition the RQ vary from 0.7 to 1.0 for carbohydrate. For ammonotelic fishes the RQ for protein is nearly 0.9. in addition an aerobic metabolism can result in RQ values between 1 and 2.

The oxyealorific equivalent Qox for carbohydrate is 5.04 kcal/l O₂ for fat, it is 4.66 and 4.69. Since the principal energy sources in carnivore s appears to be lipid and protein rather than lipid and carbohydrate, a mean Qox of 4.63 kcal/l O₂ may be more appropriate in aerobic state.