The influence of feeding level on energy distribution in fishes is an important aspect of fish physiology and aquaculture management. When it comes to energy distribution, it typically involves how the energy obtained from the food they consume is allocated to various physiological processes and growth. Feeding level, or the amount of food consumed, can have a significant impact on how this energy is distributed within a fish’s body.
Department of Fish Nutrition and Feed Technology
Central Institute of Fisheries Education, Mumbai
Energy is the ability to do work. It comes from carbohydrates, fats, and proteins and is quantitatively expressed in terms of kilocalories (kcal) or kilojoules (kJ). Energy is vital to fishes for all its physiological and metabolic needs to get fulfilled and fishes allocate energy to all the different processes taking into concern their total energy reserve so as to fulfil all their basic needs. Fishes at all stages of life have limited energy budgets (Glazier 1999; Kozlowski and Teriokhin 1999) and therefore they allocate resources among competing demands such as maintenance, growth, reproduction, and storage (Perrin 1992; Reznick and Yang 1993; McManus and Travis 1998). When energetic demands shift, a trade-off will come into place, wherein a part may get diverted to reproduction.
In case of younger fishes, they balance energy demands between growth and storage to overcome two major sources of mortality during their initial years which are predation and starvation. A strategy used by them in this concern is to allocate their initial energy to growth and then divert that allocation, at least in part, to storage in anticipation of seasonal resource shortages (Post and Parkinson 2001). This strategy allows them to attain a necessary size above that at which they are most vulnerable to predators while building storage reserves for future periods when food may get scarce. Achieving a larger size has even more advantage as per mass metabolic demand decreases with increasing size (Shuter and Post 1990; Schultz and Conover 1999). Competing demands of growth and storage are therefore strongest for the smallest, youngest fish (Post and Parkinson 2001).
Most of the evidence for fast growth followed by increased storage comes from species at high (cold, temperate) latitudes where productivity varies greatly in accordance with seasons. Far less is known about energy allocation of juvenile fishes at lower (warm-temperate) latitudes, where growing seasons are longer, periods of low winter resources are shorter, and temporal patterns of productivity are less variable.
Thus, it is said that feed and feeding level estimate the distribution pattern ultimately and it decides the amount of total energy available, with respect to which the fish distributes all its energy to different activities on a preferential basis from basic needs to reproduction and therefore this will form the important discussion of the article.
ENERGY DISTRIBUTION
The energy requirements of the animal vary in quantity according to the species, feeding habits, size, environment and reproductive state, water quality, stress etc.
Since all biological systems obey the laws of thermodynamics, the energy balance equation in fishes is represented as; C=P+R+U+F
An energy budget is the amount of energy in terms of percentage of ingested food that is utilized for each major process by fish such as growth, reproduction, digestion, respiration, urinary and faecal production. A generalized energy budget for young carnivorous and herbivorous fishes fed on natural food has been developed by Brett & Groves, 1979.
Carnivores: 100 C = 29P + 44R + 7U + 20F
Herbivores: 100 C = 20P + 37R + 2U + 4 1F
The interplay between the fish’s feeding behaviour, metabolic rates, and environmental factors influences the overall energy budget and, subsequently, growth, reproduction, and fitness. Fish that are well-fed tend to allocate more energy towards growth and reproduction, while those facing food shortages may prioritize maintenance and reduce investment in these other functions.
Energy distribution in fishes is influenced by a variety of internal and external factors like metabolic needs of the fishes, feeding level, type of feed, feed availability, quality and quantity of food taken in, feeding habit, feeding behaviour, temperature, age, size, sex, life stage, reproductive needs, level of activity, prey-predator relationship, competition, state of health, oxygen level, level of pollution and contaminants and toxins level in the environment. It is found that all these are interconnected and vary among different species and their natural habitat.
HEAT INCREMENT OF FEEDING & FEEDING LEVEL
While considering the post-prandial rate of metabolism, it was found that dietary composition and diets most favourable to growth induce the greatest effect. The magnitude of the post-prandial oxygen intake increases with increasing levels of DE in the diet. Also, the higher the proportion of digestible protein in the diet the greater the relative magnitude of this effect. The most rapidly growing fish show the greatest post-prandial increase in metabolic rate. Under conditions most favourable to growth the increase in metabolic rate following feeding is the greatest.
Most workers have found that the magnitude of the post-prandial effect increases in relation to meal size. Many (Hamada & Ida, 1973; Schalles & Wissing, 1976; Caulton, 1978; Vahl & Davenport, 1979; Jobling & Davies, 1980) have found a linear relationship between magnitude and ration size, but exponential increases in apparent SDA with increased energy intake have also been reported (Averett, 1969; Tandler & Beamish, 1979).
ENERGY DISTRIBUTION IN RELATION TO FEEDING LEVEL
Feeding levels must be high enough to supply maintenance needs and still have energy left in for growth. Efficiency of digestion decreases as feeding level is increased. The trouble is that it becomes a challenge to find a feeding level at which the increased efficiency of energy utilization at a high feeding rate is balanced by the lower efficiency of digestion at the higher feeding rate.
As ration size increases, Faecal Energy increases as a proportion of Intake Energy, efficiency of digestion and absorption decreases, growth rate decreases, energy lost in excretory products as a proportion of Intake energy decreases, HjE (Heat of Activity) increases and HwE (Heat of waste formation and excretion) declines.
The Basal or standard metabolism in fish is relatively constant under constant environmental conditions. It changes only with temperature, fish size and other confounding factors. The heat of nutrient metabolism is proportional to the level of feeding. The energy excreted in urine and gill excretions is also a function of feeding level. The reduced efficiency at high levels of feeding is shown by the proportionally large area representing faeces at high levels of feeding. The amount remaining for growth is zero at maintenance feeding and becomes proportionately greater as the feeding level is increased, until it is balanced by the decreased efficiency, of digestion.
FACTORS THAT ALTER FEEDING LEVELS TO MEET ENERGY NEEDS
Feeding rates should be adjusted in order to compensate for these factors to avoid overfeeding, while still providing sufficient energy for optimum growth and these factors are:
(a) Temperature. As environmental temperature declines homeotherms increase their metabolic rate to compensate for the additional heat loss and maintain a constant body temperature. However, most freshwater fish do not attempt to maintain a body temperature. As water temperature declines, body temperature consequently declines and metabolic rate gets reduced. The low metabolic rate at low temperatures enables fish to survive for long periods under ice where little food is available. There is considerable species difference in metabolic adaptation to environmental temperature changes as each species seems to have a preferred temperature at which it functions most efficiently. Temperature fluctuations are rare in the wild but occur in aquaculture setups. Therefore, this factor is quite significant.
(b) Water Flow. Fish which are forced to swim against a strong current expend energy which would otherwise be used for growth, while on the other hand if the water is stagnant, it causes stratification and the accumulation of waste products. Therefore, fish-rearing facilities must be designed such that maximum water is utilised wisely without undue stress on the fish.
(c) Body Size. Small animals produce more heat per unit weight than large animals. Small fish should be fed a higher percentage of body weight than large fish. Energy demand of a piece of tissue depends on the size of the animal of which it is a part. This is the scaling effect.
Y= aXᵇ
Where,
Y – any physiological variable, here metabolic rate
a – Proportionality constant
X – body mass
b – Describes the effect of size on Y
In fishes, the metabolic rate is proportional to the three-fourths power of body weight (W0.8) (commonly used). The exponent applicable is reported to range from 0.34 to 1.0.
(d) Level of Feeding and Oxygen requirement. The oxygen required per unit weight of feed varies with feeding level, being higher at the maintenance level when all the food is oxidized than at higher feeding levels when much of the energy is stored as growth.
(e) Other Factors. Several other factors can contribute to high energy requirements, such as those making fish uncomfortable, increasing physical activity and reducing growth. Crowding, low oxygen, type of feeder, light, stress and waste accumulation are some of them.
RESEARCH INSIGHTS
In accordance with a comparative study of automatic feeding and self-feeding done in juvenile Atlantic Salmon fed diets of different energy levels by Michaelis et.al., the fish groups tended to become more homogeneous in size with the passage of time in groups fed using self-feeders than in those feds using automatic feeders. Dietary energy content influenced growth and digestible energy intake of salmon fed by means of automatic feeders, but this was not seen in self-fed salmon. These results indicate that regulation of feed intake is influenced by the feeding strategy, probably because pellets are only available on demand for fish fed with self-feeders, whereas in groups fed by means of automatic feeders, pellets are freely available in excess.
As per Rasmussen and Ostenfeld (2000) and Johansen et al. (2001) feed-unrestricted salmonids grew more rapidly because they were building up greater quantities of body fat than the feed-restricted fish.
It was observed that in non-schooling fish as feed availability decreases, competition usually increases, thus dominant individuals may monopolize and acquire large proportions of the feed supply (Jobling and Koskela 1996; Saether and Jobling 1999).
The relationship between DE intake and energy gain was found to be linear in D. labrax and was independent of feed intake and body weight. The requirement for digestible energy for maintenance was calculated to be 43.6 kJ BW (kg)−0.79 day−1 and for digestible protein as 0.66 g BW (kg)−0.69 day−1. The partial efficiency of utilization for growth was 0.68 and 0.52 for digestible energy and digestible protein, respectively. These values obtained through the study were in turn used in the optimization of practical feeding for D. labrax culture.
In Haddock, it was reported that when food energy is restricted, they tend to achieve a balance between somatic growth and reproduction. When female haddock received low rations (< 5 kcal day−1) a lower proportion spawned, and the dry weights of the eggs were lower compared with females on high rations (> 13 kcal day −1).
In Blackspot Seabream, the fish condition factor (K), often used for monitoring husbandry and nutritional conditions, were significantly higher in fish fed the highest feeding level.
During a study on Portunus trituberculatus, krill oil was supplemented and it significantly promoted the growth and moulting, increased activities of ETC complexes, the membrane potential, NAD+ level, NAD+/NADH ratio and the copy number of mitochondrial DNA, up-regulated the expression levels of genes related to lipolysis, ETC and energy metabolism. Furthermore, dietary krill oil also specifically improved the free radical scavenging, reduced the level of lipid peroxides and the degree of DNA oxidative damage, mitigated the damage to mitochondrial ETC function caused by lipid peroxidation, and improved the health status of swimming crab. Overall, results of the study clearly suggested that dietary krill oil promoted the moulting and growth via enhancing the mitochondrial metabolic adaptation and ameliorating the energy homeostasis indicating the influence of feeding on body metabolism and its corresponding energy distribution.
CONCLUSION
The influence of feeding level on energy distribution in fishes is an important aspect of fish physiology and aquaculture management. When it comes to energy distribution, it typically involves how the energy obtained from the food they consume is allocated to various physiological processes and growth. Feeding level, or the amount of food consumed, can have a significant impact on how this energy is distributed within a fish’s body.
In aquaculture, understanding the influence of feeding level on energy distribution is crucial for optimizing growth and ensuring the overall health of farmed fish. Researchers use various techniques, such as calorimetry and stable isotope analysis, to study the energy distribution in fishes. Monitoring the energy allocation in fish populations helps in managing fish stocks, assessing the impact of environmental changes, and improving aquaculture practices too.
In conclusion, the feeding level of fishes directly affects growth, metabolism, and reproduction, and it is an essential consideration for fisheries management and aquaculture operations. Proper feeding practices are essential to ensure optimal energy distribution and, ultimately, the health and productivity of fish populations.
References
1. Alanärä, A., Kadri, S., & Paspatis, M. (2001). Feeding management. Food intake in fish, 332-353.
2. Brody, S., 1945 Bioenergetics and growth. London, Hafner Press
3. Cho, C. Y. (1990). Fish nutrition, feeds, and feeding: with special emphasis on salmonid aquaculture. Food Reviews International, 6(3), 333-357.
4. de Almeida Ozorio, R. O., Andrade, C., Freitas Andrade Timoteo, V. M., Castanheira da Conceicao, L. E., & Pinheiro Valente, L. M. (2009). Effects of feeding levels on growth response, body composition, and energy expenditure in blackspot seabream, Pagellus bogaraveo, Juveniles. Journal of the World Aquaculture Society, 40(1), 95-103.
5. Hislop, J. R. G., Robb, A. P., & Gauld, J. A. (1978). Observations on effects of feeding level on growth and reproduction in haddock, Melanogrammus aeglefinus (L.) in captivity. Journal of Fish Biology, 13(1), 85-98.
6. Jobling, M. (1981). The influences of feeding on the metabolic rate of fishes: a short review. Journal of Fish Biology, 18(4), 385-400.
7. Kleiber, M., 1961 The fire of life. New York, Robert E. Krieger Publishing Co.
8. Lupatsch, I., Kissil, G. W., & Sklan, D. (2001). Optimization of feeding regimes for European sea bass Dicentrarchus labrax: a factorial approach. Aquaculture, 202(3-4), 289-302.
9. Maynard, L.A. and J.K. Loosli, 1962 Animal nutrition. New York, McGraw-Hill Book Co
10. Paspatis, M., & Boujard, T. (1996). A comparative study of automatic feeding and self-feeding in juvenile Atlantic salmon (Salmo salar) fed diets of different energy levels. Aquaculture, 145(1-4), 245-257.
11. Stallings, C. D., Coleman, F. C., Koenig, C. C., & Markiewicz, D. A. (2010). Energy allocation in juveniles of a warm-temperate reef fish. Environmental biology of fishes, 88, 389-398.
12. Winberg, G.G., 1956 Rate of metabolism and food requirements of fishes. Transl.Serv.Fish.Res Board Can., (194)
13. Yuan, Y., Jin, M., Fang, F., Tocher, D. R., Betancor, M. B., Jiao, L., … & Zhou, Q. (2022). New insight into the molting and growth in crustaceans: regulation of energy homeostasis through the lipid nutrition. Frontiers in Marine Science, 9, 914590.
About Megha S Vinod
Megha S Vinod is currently pursuing her MFSc in Fish Nutrition and Feed Technology from ICAR-CIFE, Mumbai. Vinod has published over 10 articles in various journals and magazines till date. Her zone of interest is in fish nutritional studies and its biochemical evaluations.
