Microorganisms In Finfish

In healthy fish, muscle tissue or flesh is generally considered sterile. However, the fish surface and certain organs contain various levels of microorganisms: skin, 102-107/cm2; intestinal fluid, 103-108/mL; and gill tissue, 103-106/mL (2,3). Cold marine water fish mainly carry psy-chrophilic gram-negative bacteria including Moraxella, Acinetobacter, Pseudomonas, Flavobacterium, and Vibrio (4,5). Both Moraxella and Acinetobacter were designated as Achromobacter in the past (6-8). The levels of these bacteria vary somewhat depending on season and food ingested (2,5,9). Fish intestines normally contain Vibrio, Moraxella, Acinetobacter, Pseudomonas, and Aeromonas, in addition to a small number of anaerobic bacteria, including Clostridium and Bacillus. Warm-water fish carry large numbers of gram-positive, mesophilic bacteria such as Corynebacterium, Bacillus, Micrococcus, and sometimes Enterobacteriaceae or even Salmonella (4,5).

The flora of fish depends on intrinsic factors (season, fish ground, and species) and extrinsic ones (fishing method, fish handling on board, storage condition, sampling technique, medium, and incubation temperature). Trawled fish usually carry bacterial loads 10-100 times greater than those of lined fish, because fish are dragged for a long time along the sea bottom (4). The physiological condition of fish prior to death has an effect on postharvest quality. When tuna, the fastest swimming fish, are captured in a highly stressful state, the buildup of lactic acid combined with elevated muscle temperature degrade the muscle quality, although the tuna is still acceptable for canning. Salmon harvested by gill netting die after an exhausting struggle, resulting in a shorter period of rigor mortis and deterioration during icing (10). The fish should be handled as soon as possible after being landed on the vessel. Careful handling of fish with gaff hook or forks and avoiding severe physical damage are crucial. Any breaks in the skin and flesh quickly introduce spoilage bacteria, which deteriorate fish quality. Fish should be carefully cleaned, not exposed to sunlight or to the drying effects of wind, and cooled down to the temperature of melting ice (0°C) as quickly as possible (11,12).

Gutted and well-cleaned fish contain fewer bacteria than whole fish. Bleeding and gutting should be done as soon as fish arrive on deck (13). However, bleeding and gutting are not helpful in all fish harvesting operations; blue fish and dogfish are not benefited by this operation (13) if in-plant processing occurs shortly after harvest.

The method of stowing fish on the vessel can have different impacts on fish quality (14,15). Boxing, commonly used in Asia, Norway, and Iceland, provides good fish quality and quicker unloading at dockside, although it results in more labor needed in handling fish on the deck and less storage capacity. Bulking, commonly used in North America, allows for quick operation and maximum storage capacity; however, the pressure often causes poorer quality and decreases shelf life (11,16).

During the transport offish from fish ground to fish pier, bacteria grow in the fish pen or hold board at various rates depending on fish handling and storage temperature. In the bulking stow in cold weather, a slime accumulates on the bottom of the fish hold. This fish hold slime is constituted mainly of various bacteria with a level ranging from 109 to 10lo/g (17). The bacterial flora includes Moraxella, Acinetobacter, Flavobacter, pseudomonads, and heavily mucoid corynebacteria, which are the major organisms responsible for the slimy deposits and are critical problems in boat sanitation (17,18). Thorough sanitation of the fish hold after unloading the catch is necessary to insure high quality of raw fish on future trips.

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