Structure and Preservation Study of Cartilaginous Fish Sperms

Abstract

Artificial insemination (AI) plays a vital role in conserving vulnerable cartilaginous fish species, and a successful AI depends largely on sperm morphological integrity and motility. However, sperm characterization and diluents optimization for AI in cartilaginous fishes are poorly studied. Hence, we investigated the morphology, viability, and motility duration of Javanese cownose ray and black spotted stingray sperm in the ocean ringer solution. We detected that the head (Mean: 43.87 ± 0.25 µm) and midpiece (Mean: 13.83 ± 0.61 µm) length of cownose ray sperm were significantly longer than those of red jungle rooster sperm (Mean: Head; 13.83 ± 0.61 and midpiece; 4.13 ± 0.35 µm). The swimming efficiency of cownose ray sperm, VCL (Curvilinear velocity; 117.96 ± 21.04), LIN (Linearity;89.76 ± 3.69), and STR (Straightness; 96.74 ± 1.25) were markedly higher than those in rooster sperm. Such high performances might be the effect of extended head and mid-pieces of ray sperms. 

We further examined the motility percentage and motility duration shown by cownose ray sperm in seminal fluid and ocean ringer solution. The results revealed that cownose ray sperms are immotile in seminal plasma (Mean osmolality: 1151.11 ± 62.3 mlOsmol kg ^̶1), while 98% of them are motile with a motility duration of nearly 240 hours in ocean ringer solution (Mean osmolality: 1030±16.32 mOsmol kg ^̶1). We found that spermatozoa lost their integrity, and motility dropped significantly in a hyper (>1500 mOsmol kg ^̶1) or hypo-osmotic (<750 mOsmol kg ^̶1) solution. We then tried to detect the most suitable cryoprotectant and explored that glycerol (Mean motility; 59.45 ± 8.57%) provided notably better protection than dimethyl sulfoxide (Mean motility; 37.14 ± 8.25%). 

Our research is the maiden study that demonstrated the Javanese cownose ray sperm's ultrastructure along with the short-term and long-term preservation effect. Our study initiates the first step of introducing AI in cartilaginous fishes worldwide to assist the exchange of male gametes among different commercial aquaria.

Date of Award	11 May 2021
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Jiahai SHI (Supervisor)