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Macroscopic and Histological Descriptive Gonadal Study in Different Stages of Sexual Maturity of the Burmeister’s Porpoise Phocoena spinipinnis from Peru

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Diana Vega,

Koen Van Waerebeek^*,

Joanna Alfaro-Shigueto,Julio C. Reyes,Marie-Francoise Van Bressem

Diana Vega,

Koen Van Waerebeek^*,

Joanna Alfaro-Shigueto,Julio C. Reyes,Marie-Francoise Van Bressem

This version is not peer-reviewed

Submitted:

31 August 2022

Posted:

01 September 2022

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Abstract

The morphology and maturation process of gonads of 70 Burmeister´s porpoises, with body lengths ranging 135–183 cm (n= 34 females) and 64.5-182 cm (n= 36 males) were described. Samples were collected in six ports of central and northern Peru in 1987-1999. In the field, females were classified as immature, mature (resting, lactating, pregnant) and males as immature, pubescent and mature based on, respectively, the presence of ovarian corpora and the relative quantity of semen in cut epididymides. The ovaries of P. spinipinnis are ovoid or bean-shaped and flattened, with corpora modifying surface appearance. In the laboratory, ovaries were examined macro- and microscopically, measured, weighed and sliced in 1-3 mm sections. The number of corpora ovarica (lutea, albicantia, atretica) found in each ovary as well as their macroscopic and microscopic characteristics were documented in some detail. The follicles, their oocytes and nucleus were measured. Follicular development in P. spinipinnis is predominantly left-sided, but occurs in both ovaries in 16.3% of females, mainly in those with numerous corpora. Macroscopically, several corpora atretica with luteinization had characteristics similar to those of corpora albicantia, making microscopic determination essential. Inconclusive evidence of recent ovulation was found in January. Two of three immature females showed good follicular development in March and April. The body length at 50% sexual maturity in females was estimated at 152.7 cm. There was no evidence of reproductive senescence. The testes of P. spinipinnis are elongated and cylindrical. Of the 36 males examined macroscopically, 7 were immature, 5 pubescent and 24 mature. The histological analysis determining the presence and abundance of Sertoli cells, spermatogonia, spermatocytes, spermatids and spermatozoa, the relative amount of interstitial tissue, the elongation and mean diameter of the seminiferous tubules and the relative size of the lumen allowed to confidently determine sexual maturity status. The field evaluation of maturity based on the presence of sperm in the epididymides is a useful but, in 8.3% of cases, not exact method. For males the body length at 50% sexual maturity was estimated at 157 cm. No histological evidence of male reproductive seasonality was found. Spermatogenesis was perceptible year-round and tubule diameters had non-specific variations for each month.

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Subject: Biology and Life Sciences - Anatomy and Physiology

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