Semen collection and preservation in African catfish, Clarias gariepinus

Aquaflow Technical Leaflet 2002-64

European Network for the Dissemination of Aquaculture RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/

Stock improvement using quantitative and molecular genetics is an essential part of modern production of farm animals and fish. However, reproductive tissues need to be obtained without having to sacrifice broodstock. Unfortunately, male African catfish, Clarias gariepinus do not release semen under abdominal massage in captivity and need to be sacrificed in order to obtain sperm. Of course, this is regarded as a major constraint by the European catfish-farming sector. This research focused of methods to induce semen release and facilitate stripping of semen under abdominal massage and to optimise protocols for the cryopreservation of semen of the African catfish.

To facilitate hand stripping of semen, several maturational hormones that increase plasma gonadotropin levels and drugs that stimulate contractions of the reproductive tract, such as oxytoxin, were tested. The response to some of these treatments was compared between normal males and males that possess undeveloped seminal vesicles – a possible block of the sperm flow during abdominal massage. To optimise protocols for semen cryopreservation, different cryoprotectors, cooling rates and temperatures at which plunging into liquid nitrogen occurred, were evaluated.

It is unlikely that catfish males kept in captivity are strippable because of a lack of the hormone gonadotropin. Fertile semen was hand stripped from males that possessed undeveloped seminal vesicles but not from normal males, suggesting that seminal vesicles actually block the sperm flow during hand stripping. This manipulation was only possible after treatment with pituitary extract. Oxytocin may play a role in sperm transport in catfish, but more research is needed to optimise its dosage.

Catfish semen showed good tolerance to freezing and thawing. Hatching rates similar to the fresh semen were obtained with semen frozen in 10% methanol, at a cooling rate of –2, -5, -10 °C/min to –40°C and plunged into liquid nitrogen as soon as semen temperature reached –38 °C. Samples plunged into liquid nitrogen from a semen temperature above –30°C or below –50°C produced decreasing hatching rates. After thawing, semen could be diluted at least 200 times without loosing fertilization capacity. Cryopreservation of semen therefore seems to be a valuable tool for selection and conservation of genetic diversity in catfish species.

* PhD-dissertation (ISBN 90-5808-561-9; 144 pages) of Ana Viveiros

 For more information:

KOMEN Hans
Wageningen University (WAU)Fish Culture and FisheriesDepartment of Animal Sciences
P.O. Box 338, 6700 AH Wageningen,
The Netherlands
Phone : +31 317 483307
Fax : +31 317 483937

e-mail: Hans.Komen@alg.venv.wau.nl

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