Normal Microbiological Quality Of Fish And Its Significance

Introduction

Fishes are cold blooded aquatic animals, they have gills for respiration and fins for movement. Fishes are source of important nutrients, such as protein, lipid and carbohydrate. Fisheries sector provide about 3. 74% in national GDP, also contributes about 2. 7% in export earnings. So, it has become an important source of earning. They are important export products because of their high nutritious value with low fat. But fish gets contaminated in different stages after harvest by micro-organism. So, it is important to know about to know about the microbiological quality of fish and fishery products.

Large number of bacteria are found in fish’s digestive tract, as well as gill and skin. But normally they don’t cause spoilage while fishes are alive. The proportion of micro-organism which occurs on surface and guts of fishes are 102-107 CFU/cm2 and 103-109 CFU/g.

Fishes gets contaminated by different method after being harvested. During handling and processing fish and fishery products gets contaminated by pathogenic bacteria. External sources of bacterial contamination during handling are ice and salt. Crushed ice contains large number of bacterial loads.

Mainly Psychrophilic bacteria are found in the intestine of seafood such as shellfish and finfish. It is normally believed that these bacteria are found because of polluted aquatic environment.

Spoilage Microorganism of Fish

Alive fishes are considered as sterile. In dead fishes bacteria attack fish flesh, which causes spoilage and creates bad odor. The type of microorganism which causes spoilage depends on chemical composition of fish, its feeding habit, fishing gear used during harvest and the area of harvest. Common spoilage microorganism of marine fishes include Acinetobacter, Moraxella and Pseudomonas in freshwater fishes Bacillus and Micrococcus. Pathogenic bacteria such as E. coli and Salmonella are found sometimes also. These pathogenic bacteria causes diseases to human.

Mainly fish gets contaminated with pathogenic bacteria from polluted environment. Shellfish which contains such pathogenic bacteria causes different types of diseases, Paralytic Shellfish Poisoning is one of these.

Why Fish Is a Good Medium for Microbial Growth

Fish body is a ideal medium for bacterial growth. There is about 70% water content present in fish body. pH level 7-9 is also suitable for growth of microorganisms. As fish lives in water mainly psychrophilic bacteria are found in live fishes. When water content gets below 25%, microbial activity stops.

Microbial Community Changes through Different Stages

Maximum fish species lays eggs, it is believed that a part of egg microbiota comes from the mother through vertical transmission. In eggs population density of bacteria range from 103 to 106 CFU/g. As fish grows from larval to adult stage, in most fishes bacterial community decreases. Among them include Tilapia, Grass carp etc.

Effects of Environmental Condition on Microorganism

In tropical area mainly mesophilic and psychrophilic bacteria are found in Fish body. While in temperate condition, psychrophilic bacteria is mostly common. In these cold region thermophilic bacteria is almost not available.

Also pH effect the microbial growth. Microorganism can’t grow in low pH. Acidic condition prohibits their growth. Microbes prefer slightly alkaline condition.

Microbial contamination of Fish

After harvest fish can be contaminated in different stages. Fish can get contaminated during handled in boat and while in transport. If fish is processed in unhygienic condition it can get contaminated. Fish needs to be stored in good environment. If storage contains bacteria, fish spoilage rate will increase.

Microbes found in Fish SkinIn freshwater fishes, different genera of microbes are found in skin surface, these include aeromonads, Acinetobacter, Enterobacter and Micrococccus. Microbes found in marine fishes skin are Bacillus, Psudomonas and Flexibacter etc. Microbes found in Fish Gill In freshwater fishes mainly yellow pigmented rods (Cytophaga sp. ) is found. Also Coryneforms, cocci, Pseudomonas are found in gill of freshwater fish. Within the gills of marine fishes Achromobacter, Bacillus, Alcaligens and Micrococcus etc are found.

Luminescent Bacteria

Production of light by some species of fishes is a display of symbiosis between luminescent bacteria and fish. These bacteria are found in light emitting organ. Mainly photobacterium bacteria are luminescent bacteria. These bacteria are extracellular and are tightly arranged in host’s tubules.