Caracterização e impacto reprodutivo da dismorfia da papila urogenital de tilápias do Nilo

Abstract

Nile tilapia is widely produced in conventional systems due to its rusticity and adaptability to various water quality conditions, making it the third largest species produced by aquaculture worldwide. Selecting efficient breeders and identifying factors that negatively impact reproductive performance should be further investigated to ensure high productivity in tilapia farming. Additionally, reproductive problems in Nile tilapia are poorly studied, and their impact on the production chain is not explored. This study investigated in detail a reproductive dysmorphia identified in the urogenital papillae of female Nile tilapia. First, the anatomical-morphological alteration was classified, and the different degrees of involvement, its progression, association with ovarian disorders, and impact on reproductive efficiency in females with the dysmorphia were compared to those without it. In the second step, possible causal factors were explored, as well as the prevalence of the anatomical dysmorphia under different temperature conditions and genetic lineages, and the impact of these conditions on biological indices, hormonal profiles, and reproductive efficiency. In the first experiment, 96 normal females and 96 abnormal females were divided into three tanks per group. The abnormal females were used to create a classification standard for urogenital papilla dysmorphia. To determine the impact of dysmorphia on reproductive efficiency, a reproductive trial was designed and divided into three three-week cycles, with new groups of normal and abnormal females each week. The males used in the trial had normal urogenital papillae. All females and males were chipped. During the trials, water quality and reproductive variables were monitored. After the trials, the animals were euthanized, and the weights of the body, viscera, gonads, and liver were obtained to calculate the biological indices. Fragments of brain, kidney, spleen, and gonads from abnormal females were inoculated on blood and MacConkey agar for bacteriological evaluation. The results indicated that females with abnormal urogenital papilla showed lower reproductive performance. Dysmorphia of the urogenital papilla was associated with significant ovarian alterations and biological indices. Therefore, the morphology of this external reproductive structure can be used as a selection criterion for Nile tilapia broodstock. This reduced reproductive performance was not associated with bacterial disease, so other causes were investigated. In the second experiment, possible causes, such as genetic and environmental effects (temperature and bacterial agents) on the prevalence of urogenital papilla dysmorphia, were explored. Three temperature ranges were defined for investigation: 25°C-28°C (Control), 27°C-30°C (MT), and 30°C-33°C (HT). Genetic effects were evaluated with two tilapia strains: one improved body weight (G8) over seven generations of selection and another genetically unimproved (G0). The control group was created only with improved strain due to tank limitations. The animals were subjected to the same temperatures for 60 days after absorption of the yolk sac, then maintained in common tanks and chipped for individual monitoring. After reaching adulthood, the proportion of females with a urogenital papilla anomaly in each treatment and their reproductive capacity were determined. Higher temperatures during the 60 days after absorption of the yolk sac resulted in a higher prevalence of female Nile tilapia with the anomaly, with a consequent decrease in reproductive efficiency and larval production in these groups. Females with alterations in the urogenital papilla also presented significant changes in their ovaries, biological indices, and hormonal profiles. G8 animals showed a linear relationship between increasing temperature and the prevalence of urogenital papilla dysmorphia. Between 30°C and 33°C, 90% of G8 females had the anomaly, compared to 54% prevalence in the G0 lineage. In conclusion, inspection of the urogenital papilla can contribute to the selection of breeders in tilapia farming, and conducting larviculture in the first 60 days at temperatures close to 25°C prevents the occurrence of urogenital papilla dysmorphia. Finally, since the temperature ranges investigated were not extreme, the results illustrate how global warming and climate change can negatively affect tilapia production.