A review on recent techniques for elimination of fish fertilized egg adhesiveness

The eggs of many fresh water fishes become sticky after activation and contact with water. The stickiness property is caused by presence of glycoprotein molecules in outer layer of eggs. In sturgeons the fourth layer of egg (jelly coat) leaks after contacting with water. In teleosts outer zona-radiate is responsible for stickiness. Egg stickiness is important in natural reproduction, whereas eggs can attach to substrate, so brooders can locate the eggs in the best place with the most suitable environmental factors. Also the eggs can be protected by brooders that it strongly raises survival rate. But stickiness is undesirable in hatcheries clumping of sticky eggs results in mortality caused by anoxia and fungal growth. One of the phases in culture of many fresh water fishes, therefore, is to eliminate the egg adhesiveness before incubation. The methods applied for elimination the adhesiveness can be divided into 3 groups: Physical, chemical and enzymatic methods. Physical methods consist of friction the eggs gently with substances such as clay, talc powder and starch. The negative points are lower of hatching rate and time consuming of the process. The most common chemical methods are use of carbamid, tannic acid, milk powder and sodium sulfite (Na2SO3). In enzymatic methods, protease enzymes are administered to eliminate the egg adhesiveness, as the nature of the sticky layer is glycoprotein. Higher hatching rate and quick application are advantageous of this method. Hatching or embryo surviving rate, required time and the expenditure should be noticed for election the best method.