Solving the problem of
“egg sticking” in the production of tench (Tinca tinca L.)
Aquaflow Technical Leaflet 2002-79
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
Current treatments to reduce the phenomenon of eggs
adhering or sticking to each other after hatching are not particularly
effective. The elimination of “egg sticking” is therefore an important
factor for artificial reproduction and the successful incubation of eggs.
The traditional method for eliminating “egg sticking” involves stirring
for 30-40 minutes in 25 ml of milk solution per 100 g of eggs, then adding
10 ml of a fine clay suspension (20 g.l-1) and stirring for a further 10
minutes. The eggs are then rinsed with hatchery water and transferred to
Weiss jars at 18-23 0C for 60-70 degree-days (°C multiplied by the number
of days) of incubation.
A new enzyme treatment (Merck EC 3.4.21.14) to
eliminate “egg sticking” in tench was compared with standard methodology
under hatchery and fish farm conditions. Three minutes after activation the
eggs were exposed for 2 minutes to an alcalase enzyme solution. The highest
hatching rate of 87.1 % was found with 10.0 ml.l-1 enzyme treatment.
Hatching rates of ca 85 % were recorded at 15.0 ml.l-1 and 5.0 ml.l-1, but
hatching rate decreased to 80 % at 20.0 ml.l-1 enzyme. The traditional
un-sticking procedure involving milk/clay treatment gave a hatching rate of
74.1 % and required 1 hour. Under fish farm conditions the highest hatching
rate of 88.1 % was also recorded following treatment of eggs with 10 ml.l-1
enzyme, but enzyme concentrations of 7.5 and 5.0 ml.l-1 gave hatching rates
of ca 83 %. Under treatment with milk solution/clay suspension, the hatching
rate significantly decreased to only 30 %.
During the trial under fish farm conditions,
2,520,000 larvae hatched from 8,400,000 eggs (30 % of hatching) after
un-sticking of eggs with milk/clay treatment and 13,780,000 larvae hatched
from 16,600,000 eggs (83 - 88 % hatching) from the enzyme-treated eggs. No
difference in survival in nursery ponds between the fry from enzyme
treatments and milk/clay treatment was observed in the 2 years following the
initial treatment. The traditional two - step approach, based upon treating
eggs with milk solution and clay suspension, may result in inconsistent
incubation times and hatching rates, probably because of varying conditions
during propagation and use of the clay suspensions. The clay solution is
usually prepared by stirring pieces of clay soil in hatchery water followed
by straining and settling. Hence, both the size of clay particles and their
concentrations will differ between localities and trials. If the clay
suspension is too concentrated, particles stick on the egg envelope, which
results in the low hatching rate.
The application of enzyme solution shortly after
insemination greatly standardises the procedure and hence results. It has
been used for elimination of a similar problem in European catfish, and the
results of the present study showed that the method might also be used with
tench.
For more information:
LINHART O.
University of South Bohemia, Research Institute of Fish Culture and
Hydrobiology
389 25 Vodňany
Czech Republic
Phone : +420 626 424372-3
Fax : +420 626 424243
E-mail: linhart@vurh.jcu.cz