Abstract

This study was conducted in November 2006 and 2007 during an annual capture campaign as part of a long-term research project of wild Amazon River dolphins, Inia geoffrensis, in the Mamirauá Reserve in the central Amazon. Twenty-seven male botos underwent examination of the reproductive organs by real-time B-mode ultrasonography.

While the animals were out of the water they were measured, weighed, and marked .Blood, tissue samples, and swabs of several sites were taken. Ultrasound measurements (length, depth and width) of both testicles of 12 individuals were made using a Sonosite 180 Plus (C60/5-2MHz). A further fifteen individuals had to be released before completing all ultrasound measurements. Using Lambert's formula for an ellipsoid: volume (cm³) = length x width x depth x 0.71 the volume of each testis was calculated. From the sum of the left and right testicle the total testicular volume was derived and compared to body length and weight.

The body lengths and weights of the examined individuals ranged from 161 cm to 247.5 cm and 57 kg to 190 kg, respectively. Using body length to assign age class 17 males were classified as adults, 3 young adults, 5 subadults and 2 juveniles. The total testicular volume of the 12 animals with both testes measured ranged from 10.5 cm³ to 1649.6 cm³. Body length and total testes volume were correlated significantly (r = 0.62; P = 0.03). The coefficient of correlation for total testes volume and body weight was r = 0.68 (P = 0.01). Mean testis volume of the left (n = 22) and right (n = 14) testis was 222.6 cm³ (left testis) and 292.0 cm³ (right testis).

The average length of the testes was 14.13 cm (14 males; range 3.6 cm - 24.0 cm) and 12.35 cm (22 males: 3 cm 25 cm) in the right and left testes, respectively. The range of testis length was 3.1 cm - 4.3 cm in juveniles, 3 cm - 14 cm in subadults and 7 cm - 25 cm in adults.

It appears that testis length correlates to the estimated age. Data on group structure will confirm these findings. Ultrasonography of the testis is considered to be a non-invasive technique although the wild botos appeared to be more agitated during ultrasonography than during invasive procedures such as phlebotomy. The information gained from testicular size can be a useful parameter to investigate the physiology of reproduction of wild Amazon River dolphins.

Acknowledgements

This work was supported by a grant from the LMU International Office, Germany. The author wishes to thank the INPA Institution for providing the ultrasound equipment, the Projeto Boto for field support and the Instituto de Desenvolvimento Sustentável Mamirauá (IDSM) for access to the animals.