There are a number of other physico-chemical and biological water parameters aside from temperature that affect appetite of shrimps. Low dissolved oxygen levels resulting from inadequate aeration, low oxygen solubility (i.e. due to high salinity and temperature), overcast days and/or high biological oxygen demand depress feeding. The same is observed with the accumulation of metabolic wastes and water pollutants such as ammonia and hydrogen sulfide. Each of these environmental elements must relate in one way to physiological changes within the animal. Appetite also appears to be influenced by the abundance of certain plankton species. The combined action of some of these factors are synergistic (Cruz, 1991).