Decrease of reproductive performance of Nile tilapia (Oreochromis niloticus) females with dysmorphia in urogenital papilla

Abstract

The seed production of Nile tilapia (Oreochromis niloticus) can be considerably reduced when inefficient breeders are present in the broodstock. Females with dysmorphia in urogenital papilla were identified and characterized in the present study and their reproductive performance were compared to normal tilapias in three different temperatures (28 °C, 26 °C and 24 °C). We also evaluated the effects of dysmorphia in urogenital papilla on biological indexes and its possible association with pathological bacteria. From a broodstock of Nile tilapia (600 females and 150 males), 96 normal males, 96 females with normal urogenital papilla and 96 females with abnormal urogenital papilla were selected. All tilapias were individually identified by tags and reared in a biofloc system during the stocking. We performed three reproductive cycles in clear water, each one of three weeks, totalizing 9 weeks of reproduction. Different temperatures were used in each cycle, being the first at 28 °C, the second at 26 °C and the third at 24 °C. In each week, we used eight 3.6 m3 tanks with 8 females and 6 males, half of the tanks (4 tanks) had normal females and the other half with abnormal females. For each female group, there was a resting period of two weeks between each reproductive cycle. During the assays, we monitored the water quality. After reproductive assays, the animals were photographed, euthanized and the body weights, viscera, gonads, and liver were obtained for biological indexes calculation. We performed bacteriological examination, where fragments of brain, kidney, spleen, and gonads from 8 abnormal females were inoculated onto blood and Macconkey agar. The macroscopic alteration in the urogenital papilla was also associated with lesions in ovaries. The odds of females with normal urogenital papilla effectively reproduce was approximately 3, 5 and 12 times than females with abnormal papilla, in the first, second, and third cycles, respectively. The larvae number per tank produced by normal females was approximately 3, 5 and 5 times than females with abnormal urogenital papilla in the first, second and third reproductive cycle, respectively. The gonadosomatic, viscerosomatic, hepatosomatic and viscerosomatic fat indexes were not different between the normal and abnormal females. The bacteriological examination was negative for all samples. In conclusion, the morphology of urogenital papilla is a good predictor of reproductive performance of Nile tilapia and should be used for breeder selection.