USING VIBRATING TABLE DURING THE PROCESS OF EGG SWELLING IN FISH HATCHERIES

Tamás Szabó

Department of Aquaculture, Szent István University, 2100 Gödöllő, Páter K. Str. 1., Hungary

e-mail: szabo.tamas@mkk.szie.hu

Material and Methods

The vibrating table has been tested in the hatchery propagation of common carp (Cyprinus carpio), asp (Aspius

aspius), ide (Leuciscus idus), nase (Chondrostoma nasus) and tench (Tinca tinca). The table has also been used to

prevent northern pike, pike-perch and African catfish eggs from sticking together over the course of hardening.

Plastic bowls with eggs in fertilization solution were placed on top of the table. Over the 60-90 minutes of swelling

the table moving back and forth provided constant mixing of eggs preventing them from sticking together.

Inside the table there are two electromagnets with an iron core extending to them (Picture 1.). The top of the table

is attached to the iron core. The pulse repetition frequency can be adjusted in wide range by a potentiometer

through an astable multivibrator. Measurements of the vibrating table: 60 cm L × 30 cm W × 12 cm H.

Introduction

Over the courses of their natural spawning, most Cyprinids in Central-Europe scatter their eggs with an adhesive membrane. This adhesive layer sticks the eggs to submerged aquatic

plants, or to recently flooded terrestrial plants. Similarly, northern pike (Esox lucius) deposit their eggs in clear water on submerged vegetation. Pike-perch (Sander lucioperca) scatter

their eggs onto submerged plants and the male guards and fans the eggs. The eggs of African catfish (Clarias gariepinus) spawning in shallow inundated areas of lakes or rivers also have

a sticky layer situated as a disc around the micropyle.

Adhesiveness has been a selective advantage in nature, but the sticky egg shell makes artificial incubation of fish eggs impossible. To remove stickiness fertilization (Woynárovich)

solution is prepared using 40 g salt and 30 g urea (carbamide) in 10 liter of water (Woynárovich and Horváth, 1980). After the solution has been added to the eggs, fertilization occurs in a

very short time. The eggs start to hydrate and begin to swell. Eggs can be prevented from sticking together by constant mixing. Swelling and constant mixing usually last for 1.0-1.5 hours

which is time consuming and labor intensive. To reduce labor, a vibrating table replacing manual mixing has been designed.

Northern pike eggs are less sticky compared to those of Cyprinids. Therefore, freshwater can be used for the

process of swelling. However, to keep eggs from sticking, continuous stirring is necessary (Picture 6.). The

process of swelling lasting for approximately 30 min is important before transferring the eggs to the Zuger jars.

Since they are sensitive to mechanical stress, it is recommended that eggs not to be “rolled” during the first two

days of incubation. The low quantity of water flowing through the incubator enables the eggs to sink and stick

together slightly. After two days the water flow should be increased and the eggs are separated gently with a rod

or a feather. Separation is much easier if the eggs had been swollen and hardened before they were transferred

into the Zuger jars. There is also a less chance of Saprolegnia infection if the eggs come into contact with each

other on small surfaces during the first couple of days of incubation.

A recent development in the technology of pike-perch reproduction is the induction of ovulation and spermiation

by hormonal treatments in the hatchery. Gametes are collected by manual stripping and the fertilized eggs are

incubated in Zuger jars. Stickiness of pike-perch eggs should be removed before transferring them into Zuger

jars. Pike-perch eggs should be hardened for about 1.0 to 1.5 hours in a modified Woynárovich solution (20 g salt

and 15 g carbamide in 10 liter of water). To keep eggs from sticking, continuous stirring is necessary during the

hardening (swelling) period (Picture 5.). Then adhesiveness can be eliminated by tannic acid treatment (5.0 g / 10

liter hatchery water for 20 seconds).

In Europe African catfish is mainly produced in intensive systems supplied with geothermal water. Reliable seed

supply through induced breeding is one of the most important prerequisite for continuous production. The

treatment of fertilized eggs of African catfish before incubation is similar to that applied to the eggs of common

carp. Application of the vibrating table during swelling of the eggs of these carnivorous fish species was

convincing and successful.

Picture 6.: Swelling of northern pike eggs

Results and Discussion

Over the process of swelling of eggs of common carp and other Cyprinid species with economic importance the standard technology for induced breeding of common carp has been

applied (Horváth et al., 2002). Fertilization solution has been used to remove stickiness of eggs of the Cyprinid species (common carp, asp, ide, nase and tench) (Picture 2-4.). By using

Woynárovich solution instead of water, the spawn can be fertilized without the eggs sticking. The initial volume of solution added was approximately 20 percent of the volume of eggs.

The mixture was gently stirred continuously with a plastic spatula. After 10 minutes eggs were transferred from the 1.0-2.0 liter bowls into large 10-20 liter vessels. Vessels with eggs in

fertilization solution were placed on top of the vibrating table. Over the 60-90 minutes of swelling the table moving back and forth provided constant mixing of eggs preventing them

from sticking together. As the eggs swelled, additional solution was added. A portion of the solution with the dissolved sticky material was poured off at intervals and replaced. With the

help of the table approximately 4.0 to 5.0 million eggs of common carp can be hardened at the same time. After about 1.0 to 1.5 hours the swelling (and water hardening process) was

completed. The eggs were then transferred to a tannic acid solution (5.0 g / 10 L hatchery water) for 20 seconds to eliminate any remaining stickiness. To remove the tannic acid, the eggs

were thoroughly rinsed with fresh water. After tannic acid treatment, eggs were transferred into the Zuger jars. For nase and tench tannic acid treatment is not necessary, eggs can be

transferred to the Zuger jars right after swelling.

Picture 2.: Swelling of common carp eggs Picture 3.: Swelling of tench eggs Picture 4.: Swelling of asp and nase eggs

Picture 5.: Swelling of pike-perch eggs

Acknowledgments

The work was supported by the project number 8526-

5/2014/TUDPOL of the Ministry of Human Resources of

Hungary

References

Horváth L., Tamás G., Seagrave C. (Editors) 2002. Carp and Pond Fish Culture (second edition). 170 p.

Woynarovich E. and Horváth L. 1980. The artificial propagation of warm-water finfishes - a manual for

extension. FAO Fish. Tech. Pap. 201:183 p.

Picture 1.: Two electromagnets with an iron core

The vibrating table has successfully been used for many years in Hungary to reproduce different fish species

with economic importance.