Abstract
The description of sperm morphology is fundamental in the reproductive biology of fishes, but this information is limited in the family Ambassidae. Our report hence focused on the ultrastructure and morphometric analysis of spermatozoa in a pelagic fish Ambassis nalua. All fish (n = 75) were obtained during January and March 2017 from the Estuarine Pranburi River, Thailand. The standard length of fish used in this study was 3.4 ± 0.12 cm (mean ± standard deviation). All specimens were considered mature based on the abundance of spermatozoa in the testis. The testicular organs were collected and observed using standard histology and transmission electron microscopy (TEM). Ultrastructural observation associated with morphometric analysis showed that spermatozoa are structurally long cells of approximately 51.17 ± 4.54 µm total length, composed of a head, a midpiece and a tail. The head had no acrosome, and the granular structure of condensed chromatin was observed within the ovoid nucleus. The midpiece consisted of a short cylindrical region with the length of 1.29 ± 0.87 µm in diameter, having the centriolar complex organization and eight mitochondria (approx. 0.32 ± 0.02 µm each). The uniflagellar tail was clearly identified with a classical 9+2 arrangements of microtubules. Based on these characteristics, the spermatozoon of wild scalloped perchlet are considered as uniflagellate anacrosomal aquqsperm. The morphological features, including the number of mitochondria, may be used for further cryopreservation and in the evolutionary biology of this species.
Highlights
Pioneering observations on the morphology of fish spermatozoa morphology were documented by Geiger (1955) and Mattei (1970), in which varying ultrastructural features of fish spermatozoa were reported from a reproductive point of view
This finding indicates that the breeding period of wild scalloped perchlet in this area covers at least January to March, it is possible that the actual breeding period much more protracted
Our observation showed for the first time that wild scalloped perchlet spermatozoa had an oval head, eight mitochondria and the axoneme of the sperm tail
Summary
Pioneering observations on the morphology of fish spermatozoa morphology were documented by Geiger (1955) and Mattei (1970), in which varying ultrastructural features of fish spermatozoa were reported from a reproductive point of view. The aquasperm spermatozoa have a round head, a short neck region (mid-piece), and a few mitochondria (Jamieson, 1991). This type of spermatozoa is associated with external fertilization (Jamieson, 1991), which has been found in 97% of all teleosts (Lahnsteiner et al, 1990; Jamieson, 1991; Quagio-Grassiotto et al, 2005; Maricchiolo et al, 2007), as reported in several species such as Lates calcarifer (Jamieson, 1991), Pagrus major (Hara and okiyama, 1998), Pagellus bogaraveo (Maricchiolo et al, 2010), Rastrelliger brachysoma (Senarat et al, 2018a) and Allenbatrachus grunniens (Sukkhee et al, 2021). The introsperm spermatozoa have an elongated head, but the mid-piece is known to be missing (Mattei, 1991; Jamieson and Grier, 1993; Jamieson, 1991). The introsperm spermatozoa have been found in fishes of at least 24 teleostean families (Reznick et al, 2002; Burns & Weitzman, 2005) that undergo internal fertilization (Jamieson and Grier, 1993; Jamieson, 1991)
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