Physiological responses of the Asian Sea Bass, Lates calcarifer to water quality deterioration during simulated live transport: acidosis, red-cell swelling, and levels of ions and ammonia in the plasma

Abstract

Water is a major expense when air-freighting live fish. However, reducing the volume of water relative to the amount of product usually results in more rapid water quality deterioration and higher mortality due to the higher concentration of excretory products in closed transport systems. The major water quality effects experienced by fish during transport are: low dissolved oxygen levels due to oxygen consumption by respiration; accumulation of carbon dioxide from respiration; depression of pH caused by carbon dioxide accumulation; and increased ammonia levels resulting from ammonia excretion.

The physiological responses of seawater-adapted barramundi, Lates calcarifer, were studied during simulated live transport and transport under circumstances of elevated CO2 or NH3. Blood samples were removed from fish exposed to these treatments and compared to samples from control fish, (free in the tank) and fish confined in a box but with free-flowing seawater. Analysing the blood samples showed that simulated transport caused the plasma pH of the fish to fall, threatening the blood's ability to transport oxygen, but the red blood cells apparently defended their internal pH and oxygen transport capacity, and swelled measurably as a result. Exposing fish to unusually high carbon dioxide or ammonia levels caused plasma pH to fall to near lethal levels. The effects of both carbon dioxide and ammonia need to be considered when studying the responses of barramundi to live transport. Water quality parameters during fish transport do not act in isolation. Attempts to reduce carbon dioxide accumulation, for example, by using a buffer to control the water pH, may influence the fish's ability to excrete ammonia.