A dynamic model for simulation of growth in pigs was extended by a module to assess maximum and minimum heat loss (HLcold, HLhot) for a given pig, to compare these figures to heat production (HP), and to take thermoregulatory action when HP < HLcold (cold conditions) or HP > HLhot (hot conditions).

HLcold and HLhot were largely determined according to algorithms obtained from the literature, hut HLcold was made dependent on body fat depth through tissue insulation. Data to establish the relation (Ύ = 0.05 + 0.002 x X) between cold tissue insulation (Ύ in °C.m2 per W) and backfat depth (X in mm) independent of body weight were obtained from the literature. The same data showed that HLhot is not related to backfat depth in pigs.

Cold thermoregulatory action included an increase of ad libitum food intake. Hot thermoregulatory action included reduction of physical activity, increase of body temperature, wetting of a proportion of the skin and reduction of dia libitum food intake.

A sensitivity analysis showed that the model’s output in terms of ãd libitum food intake, HP, protein deposition (Pdep) and lipid deposition (Ldep) is strongly sensitive to the characterization of the genotype being simulated. The model was used to simulate trials from the literature. Although the model does not explicitly calculate lower and upper critical temperatures, these could be adequately predicted from its output. Comparison of model output with experimental data revealed an adequate prediction of ad libitum food intake and of the partitioning of ad libitum ingested metabolizable energy (ME) into HP, Pdep and Ldep in cold, thermoneutral and hot conditions. At restricted ME intake, and especially in cold conditions, the model tends to overestimate HP and underestimate Ldep, probably because it does not take account of long-term acclimatization.

Emphasis on physiological adaptations to environmental changes in the catfish (Siluroidei), is a rather recent development like that of their use in aquaculture. The siluroid fishes with smooth scaleless skin and sensory barbels are adapted to live in a variety of aquatic environments ranging from freshwater and brackishwater to swamps and marshes both in temperate and tropical regions. However, very little has been explored on their expected wide range of physiological adaptations. Most of the results obtained in siluroid fishes are similar to those reported for other teleosts such as cypriniform species. However, there are some air-breathing siluroids, found in the tropical areas, with accessory air-breathing organs. Besides tolerating periods of water deprivation, some of these fishes have been shown to possess-special physiological and biochemical adaptive mechanisms to tolerate a wide range of adverse physico-chemical conditions in the ambient environment. Some of the physiological adaptive mechanisms of Siluroidei in general, and air-breathing species in particular, to important physico-chemical factors such as oxygen,temperature, ammonia and xenobiotics are reviewed and discussed.