Fish, like other living systems, must conform to the laws of thermodynamics. Fish gain matter and energy in food, and they lose absorbed matter and energy as a result of catabolism—which provides energy for maintenance and activity—and the elaboration of reproductive products. Physiological energetics, or animal bioenergetics, concerns the rates of energy expenditure, the losses and gains, and the efficiencies of energy transformation, as functional relations of the whole organism. The majority of such presentations commence with an energy-flow diagram indicating the main steps that the energy of food intake follows through the organism, and the paths of energy distribution. Each of these steps with their appropriate values is subject to quantitative change, depending on many biotic and abiotic factors. With the thought that the basis of these energy exchanges needs to be elaborated first, it was deemed more fitting to conclude with a quantitatively expressed flow diagram. An understanding of the physical, chemical, and biological basis on which the energetics is built, and the equivalents employed, constitutes the opening section of this chapter. Some necessary distinctions between mammalian and nonmammalian systems are made. An adequately nutritious diet is assumed; the basic source of fuel for the fire of life is solely derived from the food.

6 – Physiological Energetics

To understand how the many environmental factors influence growth, the basic rate functions should never be lost sight of, despite the general simplicity of growth measurements. As far as possible, the individual functions have been introduced in the chapter to provide some explanation of the response to environmental factors, without deviating from the major purpose of examining the recorded trends in the activity of growing. In relation to environmental effects, quite obviously growth cannot be studied without involving food consumption, even though the latter may not necessarily be measured. In this respect, growing—unlike such activities as swimming or respiring—is inseparably coupled with a powerful biotic factor, so that any abiotic factor is necessarily involved in some form of interaction between the two. Growth rate may either increase or decrease depending on the nature of the food × metabolism × temperature relation; on analysis it can be seen that the energy demand of elevated metabolic rate could have exceeded the gain from increased food uptake resulting in reduced growth rate. Furthermore, the act of growing necessarily alters size so that another important biotic factor continually changes with time. An understanding of these inherent involvements is necessary before any clear insight of the environmental relation to the growth process can be achieved.

10 - Environmental Factors and Growth

synopsis. Ectothermic vertebrates respond to the temperature of their habitat in a manner that is remarkably similar to their response to more traditional ecological resources such as food. We review the response to temperature primarily from literature on fishes in terms of ecological concepts related to niche theory and competition. The width of the fundamental thermal niche is about 4?C when measured by a mean plus and minus one standard deviation of the distribution of temperature occupied in a laboratory gradient. Fish of temperate freshwater appear to fail into three thermal guilds along the temperature re? source axis ?cold, cool, and warm water fishes. Realized thermal niches are similar in central tendency to fundamental niches, but niche width appears to be more narrow for the realized niche in limited sample data. The success of interference competition for space with preferred temperature is tied to social dominance in a manner analogous to food competition. Thermal niche shifts in the face of interspecific competition for preferred temperature appear supported by one laboratory study. Exploitation competition in re? spect to temperature seems nebulous. If animals successfully compete for their thermal niche, growth and perhaps other measures of fitness are maximized. Cost/benefit models for thermal resources and food resources lead to similar predictions about resource use. We suggest that viewing temperature and other niche axes in the way ecologists have viewed food resources would be useful.

Temperature as an Ecological Resource

Despite uncertainty in all levels of analysis, recent and long-term changes in our climate point to the distinct possibility that greenhouse gas emissions have altered mean annual temperatures, precipitation and weather patterns. Modeling efforts that use doubled atmospheric CO2 scenarios predict a 1–7°C mean global temperature increase, regional changes in precipitation patterns and storm tracks, and the possibility of “surprises” or sudden irreversible regime shifts. The general effects of climate change on freshwater systems will likely be increased water temperatures, decreased dissolved oxygen levels, and the increased toxicity of pollutants. In lotic systems, altered hydrologic regimes and increased groundwater temperatures could affect the quality of fish habitat. In lentic systems, eutrophication may be exacerbated or offset, and stratification will likely become more pronounced and stronger. This could alter food webs and change habitat availability and quality. Fish physiology is inextricably linked to temperature, and fish have evolved to cope with specific hydrologic regimes and habitat niches. Therefore, their physiology and life histories will be affected by alterations induced by climate change. Fish communities may change as range shifts will likely occur on a species level, not a community level; this will add novel biotic pressures to aquatic communities. Genetic change is also possible and is the only biological option for fish that are unable to migrate or acclimate. Endemic species, species in fragmented habitats, or those in east–west oriented systems will be less able to follow changing thermal isolines over time. Artisanal, commercial, and recreational fisheries worldwide depend upon freshwater fishes. Impacted fisheries may make it difficult for developing countries to meet their food demand, and developed countries may experience economic losses. As it strengthens over time, global climate change will become a more powerful stressor for fish living in natural or artificial systems. Furthermore, human response to climate change (e.g., increased water diversion) will exacerbate its already-detrimental effects. Model predictions indicate that global climate change will continue even if greenhouse gas emissions decrease or cease. Therefore, proactive management strategies such as removing other stressors from natural systems will be necessary to sustain our freshwater fisheries.

/pdf/potential-impacts-of-global-climate-change-on-freshwater-4agnfth259.pdf

Potential impacts of global climate change on freshwater fisheries

https://webpages.uidaho.edu/fish511/readings/readings 2010/energy of invertebrates.pdf

Energy Homeostasis as an Integrative Tool for Assessing Limits of Environmental Stress Tolerance in Aquatic Invertebrates

The study of animal function is organized more or less under three heads, which in everyday language are, as applied to a machine, what it can do, how it works, and what makes it go. Insofar as fields of study can be classified in biology these divisions of the subject are ordinarily considered to be autecology, physiology, and biochemistry, with a great deal of individual taste governing the label any particular worker may choose for himself. The chapter discusses what fish can do in relation to their environment and therefore largely autecology. The chapter focuses on the action of the environment on metabolism and the effects of this action on the activity of the organism.

F.E.J. Fry

Papers

1 – The Effect of Environmental Factors on the Physiology of Fish