Viability, motility, ATP content and fertilizing potential of sperm from Atlantic salmon (Salmo salar L.) in milt stored before cryopreservation

Elisabeth Kommisrud,Frøydis D Myromslien,Else-Berit Stenseth,Teklu T Zeremichael,Nadine Hofman,Inger Grevle,Jan Sunde

doi:10.1016/j.theriogenology.2020.04.008

Elisabeth Kommisrud, Frøydis D Myromslien + Show 5 more

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https://doi.org/10.1016/j.theriogenology.2020.04.008

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Abstract

Artificial fertilization is increasingly used in aquaculture, mostly applying short-term cold stored milt. Large scale cryopreservation of milt could be valuable for increased flexibility and acceleration of breeding progress. The aim of this study was to assess viability, motility and ATP content of sperm from Atlantic salmon as a function of storage time, before and after cryopreservation. The objective was also to investigate whether in vitro parameters were associated with sperm fertilizing ability after cryopreservation. Milt from six mature Atlantic salmon males were collected twice, one week apart. The milt was stored undiluted at 5 °C in cell culture flasks for six days. Samples were taken on days 1, 3 and 6 of storage for cryopreservation. In total, 36 batches were diluted to a standardized sperm concentration of 2 × 109 spermatozoa/mL, filled into 0.5 mL French medium straws and cryopreserved. In vitro analyses were assessed on the same sample for the 72 combinations of male, collection week, days of storage and cold stored or frozen-thawed. Fertilization trials with cryopreserved milt were carried out for all 36 batches in triplicate for each combination of male, collection week, storage time and sperm:egg ratios of either 2 or 4 × 106 sperm per egg, respectively, totally 218 experimental units, including two egg controls. There was a significant influence of storage and collection week on sperm quality parameters, both cold stored and cryopreserved, and cryopreservation had a significant effect on all tested sperm quality parameters. High correlations for cold stored vs cryopreserved samples was demonstrated for ATP content (p < 0.00001), motility and velocity parameters (p < 0.001), but not for viability, straightness and linearity. The overall percentage of fertilization achieved was 73.9 ± 1.7%. Sperm collected in week 2 showed significantly lower fertility when cryopreserved after six days of storage than after 1 or 3 days for sperm to egg ratios of 2 × 106 (p < 0.005), while there was no such effect for milt collected in week 1. Several post-thaw sperm parameters were correlated to fertilization rates, while curvilinear velocity best explained variations in fertilization by modelling. Our results suggest that cryopreservation of Atlantic salmon milt should be performed soon after milt collection to maximize the cryopreserved sperm quality. Fertilization results seems not to be compromised by storage for three days before cryopreservation.

Highlights

Fresh, liquid stored, or cryopreserved semen is used for artificial insemination (AI) worldwide and is the most valuable tool for breeding and genetic improvement in agriculture [1], and increasingly used for artificial fertilization in aquaculture.E
The results of our study show that milt from Atlantic salmon preserve fertilizing capacity during cold storage and subsequent cryopreservation, even though in vitro quality parameters were significantly negatively influenced by both storage and cryopreservation
Fertilization was not affected by storage prior to cryopreservation when applying milt collected the first week of the experiment, which could be consistent with a report of maintained fertility of milt stored for 10 days at 0 C [14]

Summary

Introduction

Liquid stored, or cryopreserved semen is used for artificial insemination (AI) worldwide and is the most valuable tool for breeding and genetic improvement in agriculture [1], and increasingly used for artificial fertilization in aquaculture.E. The large number of fish species and significant differences between species has partly limited the interest in cryopreservation of milt to research [5]. The aquaculture industry has adopted short term refrigerated storage of milt, a method that offers limited flexibility compared to cryopreservation. This paper explores if cold storage of milt for a short period can be followed by cryopreservation without compromising postthaw sperm quality and fertilizing potential. This combination would increase the flexibility and applicability of cryopreservation. To our knowledge the service of large-scale commercial cryopreservation of fish sperm is currently offered by a single commercial provider (Cryogenetics AS, Norway)

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