Metabolism

Everything the fish performs requires energy. From respiration over the gills, osmoregulation, excretion of ammonia or locomotion. The energy is a result of chemical reactions (metabolism) performed by the organism. These reactions usually require oxygen too. Metabolism is a term that describes the body’s energy expenditure per unit of time. As long as there are no anaerobic processes, the rate of oxygen consumed is closely linked to metabolism (oxidation).

The metabolism involves both catabolism and anabolism. Catabolism is the process of breaking down metabolites to produce active energy. Anabolism uses those same products to build new tissue for growth, maintenance and reproduction.

The energy intake from food falls into three categories. Gross Energy or GE is the total energy released by food as measured with a calorimeter. The Digestible Energy or the DE of food is the amount that is utilized and digested, minus the portion that ends up in the feces. The remaining energy actually used by the animal is the Metabolizable Energy or ME. Osmoregulation consumes 25 to 50% of the total metabolic energy output in fish (Morgan & Iwama, 1999. Laiz-Carrion, et., al, 2002)!

Hormones such as cortisol
- A high level of cortisol in the bloodstream increases metabolism as it accelerates the energy demand for osmoregulation.
Environmental conditions: temperature, salinity, oxygen level
- Metabolism and oxygen demand increases as the water temperature rises.
- The oxygen-carrying capacity of water declines as the temperature increases.
- Large temperature changes slow metabolic recovery and lactic acid removal in the fish.
Level of the animal's activities.
- Active swimmers consume more energy in locomotion than inactive or sedentary fish.
Size of the animal: larger fish have a lower metabolism rate per unit of weight.
Age because of growth and reproduction energy costs.
- Young fish require a large portion of energy for growth.
- Larger specimens will have a slower metabolism than their smaller counterparts will.
- More saline environment require more energy spent on osmoregulation (increasing the metabolic rate)
Health or condition: repair consumes energy.
Intraspecific variation in metabolic rate during the ontogeny.

Diffusion of respiratory gases is a size-dependent process and is very important during early life history. In addition, a large amount of energy is required to support the large growth rate. Hence there are physiological differences between larval stages. During 32 days, the oxygen consumption in zebrafish increased approximately threefold (Figure 2A) in a study by Bagatto et al.,(2001). However, oxygen uptake decreases in relation to body weight (Figure 2B).

Figure 2: A) Oxygen consumption and B) mass-specific oxygen consumption in zebrafish from yolk sac larvae until free swimming larvae.

Bagatto, B., Pelster, B., & Burggren, W. W. (2001). Growth and metabolism of larval zebrafish: effects of swim training. The Journal of Experimental Biology, 204, 435-4343.

Laiz-Carrion, R. Sangiao-Alvarellos, S. Guzman, J.M. Martin, M.P. Miguez, J.M. Soengas, J.L. Mancera, J.M. (2002) Energy metabolism in fish tissues related to osmoregulation and cortisol action: Fish growth and metabolism. Environmental, nutritional and hormonal regulation. Fish Physiol and Biochem, 27(3-4), p. 179-188.

Morgan, J.D. Iwama, G.K. (1999) Energy cost of NaCl transport in isolated gills of cutthroat trout. Am J Physiol, 277(3 Pt 2), R631-639.

What affect the rate of metabolism?

Metabolism and scaling

References