64 DECEMBER 2013 • WORLD AQUACULTURE • WWW.WAS.ORG Hungary has a strong tradition of pond farming and induced fish breeding. Different breeding methods ensure that increasing demand for high quality fish meat in Hungary and foreign markets is met. One of the most important fish species of domestic fish farming is common carp Cyprinus carpio. The artificial breeding of common carp has been carried out by efficient technological steps in hatcheries for decades. The most important carnivorous fish species in carp ponds is wels catfish Silurus glanis. Some fish species, such as common carp and wels catfish, have so-called phytophilic eggs (Bíró 1993) that have a sticky protein material on the surface of the fertilized and swollen egg that facilitates attachment to vegetation in nature. In nature, the incubation and hatching of eggs takes place while attached, usually to aquatic plants. During artificial breeding this characteristic has a negative effect on the success of hatching because eggs stick together. Therefore, trapped eggs cannot obtain sufficient oxygen and the developing embryo dies. Different molds can appear on the surface of dead eggs and, when mold starts, it is harmful to adjacent eggs. Tannin, also known as tannic acid or acidum tannicum, is a highly tanning, astringent, polyphenolic plant compound. Tannin precipitates proteins and other organic compounds, including amino acids and alkaloids; it also decreases the swelling of collagen. It is not a chemically uniform compound (Straub 1975). Pure tannic acid is a white and amorphous powder but exposure to air causes it to become yellowish. It is soluble in water, less soluble in alcohol and glycerin, and insoluble in ether. During artificial breeding in hatcheries, technicians often add tannin to eggs after fertilization for the irreversible termination of stickiness. After treatment with tannin, eggs incubated in Zug jars do not stick together or form lumps, thereby increasing the efficiency of hatching. However, if the concentration of tannin and the duration of use are not appropriate, the quality of eggs is impaired. Effect of Tannin Treatment on the Hatching of Common Carp and Wels Catfish Eggs Z. Bokor, B. Csorbai, I. Ittzés , D. Ács, B. Urbányi and F. Fodor Tannin is widely used in common carp hatcheries. Tannin is also used in the breeding of other commercially important fish species, such as catfish and perch. In artificial breeding, tannic acid treatment is the last action before fertilized and swollen eggs are placed into Zug jars. The tannin solution precipitates the protein produced on the surface of the egg and prevents its stickiness. As a side effect, tannin also hardens the wall of the egg. Consequently the developing embryo hatches with difficulty. In light of the two effects (removal of stickiness and hardening of eggs), it is important to precisely define the tannin concentration of the solution and the duration of treatment. Different instructions for use of tannin have spread among practitioners but many fear the negative effects of tannin. However, concerns and instructions for use may be unjustified in some cases. The objective of this study was to assess the effect of tannin concentration and treatment duration on the quality and time of hatching of eggs and survival of embryos. These are defined with respect to the characteristics of eggs of particular species. Thus, the effects of tannin were examined on eggs of common carp and wels catfish, at four concentrations and three treatment durations. Experimental Design Determination of test concentrations and egg treatment durations were based on references from the published literature and personal communication with practical technical experts. Four tannin concentrations (0.1, 0.5, 1 and 10 g/L) and three treatment durations (5, 20 and 120 sec) were established. The standard practice is treatment with a tannin solution of 0.5 g/L for 20 sec. Each treatment combination was applied to three portions of eggs. Each egg portion was treated by different concentration-time combinations and then rinsed in fresh water. After application of tannin, 50 eggs from each treatment combination were placed in Petri dishes and incubated under a drip system. Incubation in Zug jars was not practical because the FIGURE 1. The egg hatching drip system with Petri dishes (Photo: Zoltán Bokor).
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