DNA fragmentation and membrane integrity in sperm of farmed Arctic charr (Salvelinus alpinus)

Henrik Jeuthe,Christos Palaiokostas,Anders Johannisson

doi:10.1016/j.aquaculture.2021.737537

Henrik Jeuthe, Christos Palaiokostas + Show 1 more

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https://doi.org/10.1016/j.aquaculture.2021.737537

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Abstract

Despite the relatively long history of captive breeding, the Arctic charr still exhibits a generally low, but highly variable reproductive performance in aquaculture. A recent publication exposed potential paternal factors influencing the reproductive outcome of Arctic charr broodstock from the Swedish breeding program. Interestingly, the paternal factor appeared to be more closely connected to embryo survival than to fertilisation rates. This lead to speculations on whether e.g. chromatin related issues, potentially related to oxidative stress could be involved. In order to investigate this hypothesis the present study assessed the levels of DNA fragmentation, using the SCD-method, and membrane integrity, using flow cytometry, in sperm of farmed Arctic charr. Moreover, the existence of associations was tested between DNA fragmentation and membrane integrity in individual semen samples and viability of their resulting progeny. We found high levels of DNA fragmentation in sperm from the Arctic charr sires, ranging from 24% to 86% with a median of 67%. Membrane integrity values were high, with individual levels of 93.1% to 99.6% viable sperm cells, median 98.8%. DNA fragmentation and membrane integrity values were moderately correlated (r = 0.304, p < 0.05). Fertilisation rates and proportions of eyed eggs showed substantial individual variation and were correlated (r = 0.497, p < 0.05). However, large differences between proportion of eyed eggs and fertilisation rate, median 52% and 81.6% respectively, highlight that the main loss occurred due to embryo mortality rather than failed fertilisation. No correlation was found between either DNA fragmentation or membrane integrity and the resulting reproductive outcome (fertilisation rate and eyed eggs) of the individual Arctic charr sires. Overall, our study identified very high levels of DNA fragmentation, which could influence the fertility of the broodstock in question and thereby be a mitigating mechanism involved in the low reproductive success most often observed in farmed Arctic charr. Further exploration of this relationship would be needed, though.

Highlights

The Arctic charr (Salvelinus alpinus) is an important fish species for freshwater aquaculture in the Nordic countries
Poor egg quality is a well-known issue in Arctic charr hatcheries (Jobling et al, 1998) and is, at least in part, caused by inadequate rearing conditions (Jeuthe et al, 2015) which disturb the process of oocyte matura tion and ovulation (King et al, 2003)
In order to investigate this hypothesis the present study assessed the levels of DNA fragmentation and membrane integrity in sperm of Arctic charr sires from the Swedish breeding program

Summary

Introduction

The Arctic charr (Salvelinus alpinus) is an important fish species for freshwater aquaculture in the Nordic countries. Despite the relatively long history of captive breeding, the species still exhibits a generally low but highly variable reproductive performance in aquaculture. One study on Arctic charr broodstock showed rapid changes in sperm quality over generations as an effect of captive selective breeding (Kekalainen et al, 2013). During the last de cades there has been an increased research focus on the sensitivity and complexity of male reproduction in fish and the impor tance of good quality sperm, to achieve fertilisation and for embryonic development (Cabrita et al, 2014; Herraez et al, 2017)

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