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RP2E INRA Université de Lorraine

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Sex determination and egg quality evaluation in Eurasian perch, Perca fluviatilis, using ultrasonography

5th International Workshop on the Biology of Fish Gametes, 07-11 septembre, Ancone, Italie

Schaerlinger, B., Staub, C., Touze, J.-L., Chardard, D., Krauss, D., Ledore, Y., Alix, M., Fontaine, P.

2015

INTRODUCTION

Among the temperate freshwater fish species, the flesh of percids is very appreciated by consumers. As a consequence percid breeding becomes an interesting market and several fish farming focus on pike-perch and Eurasian perch production. Perch reproduction cycle last for 9 months and is under the control of the temperature and the photoperiod (Abdulfatah et al., 2011). Even if female oogenesis is induced, the reproduction success remains variable. In addition, as for many fish species, there is no sexual dimorphism for the Eurasian perch. As a consequence, scientific studies investigating either oogenesis or reproduction success and fish farmers wishing to check perch oogenesis need to sample some fish in their tank. This is also true with other fish species. In order to find a way to make early sex determination and check oogenesis process, we used ultrasonography on perch. This technique as used with success with several other fish species (for review Novelo and Tierch 2012) to study oogenesis process. This technique has the advantage to be non invasive and to allow accurate study of fish gonadogenesis. The present study aimed at presenting first data obtained to (i) to determine the sex of Eurasian perch individuals, (ii) to define correlations between parameters obtained using ultrasonography and regular methods and (iii) to predict potential egg quality.

 

MATERIALS AND METHODS

Two populations of Eurasian perch (wild and domesticated) were used in this study and all individuals had been furnished by the fishfarm “Lucas Perches” (Hampont, France). In total, around 300 fish have been reared in our facilities from the larval stages. Their reproduction was induced using a photo-thermo-periodic program previously developed in our laboratory (Abdulfatah et al., 2011). Three and five months after the beginning of the induction, ultrasonography experiments have been performed to study fish gonadogenesis on a sample of 30 females. Experiments have been performed using a MyLab30 Vet gold apparatus (Esaote-Piemedical) using a LA332 probe (Hospimedi France) 3-10 Mhz. The frequency was low (6 MHz) to allow a penetration of the sound waves for at least 5 cm. The area and the perimeters of the gonads were measured on ultrasonography picture. Every fish was put to death, weight and measured. Their gonads were dissected, weighted, photographed and fixed in Bouin’s solution to perform histological studies. The gonado-somatic index was calculated and a comparison of data obtained with the two techniques.

 

RESULTS

The experiment was first performed three months after the beginning of the induction. It appeared that the sex determination was already possible at that time with an accuracy of around 94 %. Two months later we almost obtained 99% of success. The ovaries appeared as mass punctuated by light dots corresponding to the oocytes. On the contrary, testes were less evident to discern and appeared mainly as two black lobes separated by a white line.

We measured the ovary area and perimeter for 30 females by ultrasonography and compared it with the gonad weight and the GSI. It appears that these parameters are poorly correlated indicating that we need to accumulate other information to better evaluate oogenesis progression.

Finally, we observed on the echography pictures several pockets of liquid for some fish. These observations were confirmed after dissection and were not present for every fish. Moreover, the egg density in the ovary was also observed and showed that it was not homogenous in every case. Finally, we observed a scale from white to dark gray colors for the oocytes, suggesting that the lipid content may be variable between oocytes. Indeed the gray scale obtained depends on the lipid/water relative composition. These information are important because it could preset reproduction impairment. Indeed, the accumulation of lipid is one of the key elements to confer a good quality to the ova.

 

DISCUSSION AND CONCLUSIONS

Several studies investigated the possibility to identify the sex of fish that don’t present any external sexual dimorphism. For the Eurasian perch this determination was successful 3 months after the beginning of the gonadogenesis as observed in other studies (Novelo and Tierch 2012). However, our measurements failed to characterize efficiently the oogenesis progression. In other studies, several calculations were proposed to make this characterization (Novelo and Tierch 2012). Those reproductive indexes all seem reliable but a comparative study needs to be performed to better characterize them. Finally, few studies tried to find criteria presetting ova quality and reproduction success. We observed that the internal organization of the ovary (liquid pocket formation, oocytes density) and the oocyte lipid/water content may be easily observable. The comparison with histological study of the gonads (still under investigation) will help us to better characterize this point. Ultrasonography appears as new methodology to study fish gonadogenesis because it is non-invasive and easy to perform. This new approach already gives good results for sex identification, it also opens new avenue o research especially for the early determination of ova quality.

 

AKNOWLEDGEMENTS                                                                                   

This work was supported by Research Ministry (PhD fellowship of M.A.), INRA Department PHASE and the Lorraine region.

 

REFERENCES

Abdulfatah, A.; Fontaine, P.; Kestemont, P.; Gardeur, JN.; Marie, M., 2011: Effect of the photothermal kinetics and amplitude of photoperiod decrease on the induction of the reproduction cycle in female Eurasian perch Perca fluviatilis. Aquaculture 322-323, 169-176.

Novelo, ND.; Tiersch TR., 2012: A review of the use of ultrasonography in fish reproduction. North American Journal of Aquaculture 74,169-181.

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