HARVEST AND TRANSPORT OF LARGEMOUTH BASS
The food-fish market for largemouth bass (Microperterus salmoides) is somewhat unique in that the fish are typically marketed live to the consmer. This requires that the physiological condition of the fish following harvest and transport to market is sufficient to endure the additional step associated with marketing from retail display tanks over a period of several days to weeks. Fish are subject to aerial exposure, crowding, net handling, and environment changes during harvest and loading for transport. These handling processes have the potential to cause stress. The severity of the stress response and the length of time before homeostasis is regained are directly related to the duration of the stressor and the characteristics of the recovery water.
Research on largemouth bass has shown that plasma glucose and corticosteroid values are good indicators of stress during application of acute stressors, whereas chloride and osmolality are more useful indicators of long-term stress. "Delayed mortality" might occur days or even weeks after transport depending on the underlying cause and severity. Some mortality during and following largemouth bass transport is common and generally accepted as "the nature of the business" if mortalities are less than 1% of the total load. Producers frequently add 1-2% extra fish by weight to compensate for losses due to mortality and "shrinkage" associated with bodily waste elimination.
During the summer months, largemouth bass are typically not harvested for food fish sales due to increased stress and mortality associated with warmer waters in conjunction with harvest, holding and the transport necessary to supply distant live markets. Producers primarily market their fish only when pond water temperatures have stabilized below 18oC. Live haulers typically add evaporated salt to hauling containers at 2-3 g/L (ppt) to aid in osmoregulation. Since fish are cold blooded, lowering water temperatures reduces metabolic activity, oxygen consumption and waste excretion and increases the oxygen carrying capacity of water. As a general protocol the water temperature should not be reduced more than 1oC every 15 minutes and not exceed 12oC over a 24-hour period for largemouth bass.