Egg and sperm quality in fish
Introduction
The control of reproduction is a key issue in aquaculture and one of the limiting factors of the reproductive success is the quality of male and female gametes. Gamete quality in the wild, or in captivity, is influenced by many factors and is sometimes highly variable. For this reason, gamete quality has received increasing attention and many studies have characterized the effect of specific factors on egg or sperm quality. The issue of fish egg (Kjörsvik et al., 1990, Brooks et al., 1997) and sperm (Billard et al., 1995) quality has previously been reviewed. Yet, the picture of the factors that can significantly affect gamete quality remains incomplete. The relative effects of each factor on gamete quality can be highly variable and are not always well characterized. In addition, the definition of gamete quality is not always consistent among existing studies and several types of indicators have been used to assess gamete quality. Finally, the knowledge of the role of some intracellular gamete components on the quality of the gamete has benefited from recent studies, including genomic-based investigations that have provided new hints on the long-term process of understanding what is and what makes a good egg and a good spermatozoon.
The present review is therefore aiming at (i) briefly presenting the molecular and cellular characteristics of fish gametes with special attention paid to the molecular actors that could play a key role in the regulation of gamete quality, (ii) defining what is egg and sperm quality and how can it can be accurately estimated or predicted, and (iii) providing an up to date review of the factors that can impact gamete quality in teleosts.
Section snippets
Egg
The unfertilized egg or female gamete is an oocyte arrested in metaphase of the second meiotic division. This metaphase 2 oocyte is the final product of the oogenetic process that occurred within the ovary throughout oogenesis (Tata, 1986). As a consequence, the coordinated assembly of the egg can last for a very long time, up to several years in some species. Hence, the incorporation, synthesis, and processing of egg components that occur during oogenesis play a key role in the coordinated
What is egg/sperm quality and how can it be estimated or predicted?
From a biological standpoint, the quality of a gamete can be defined as its ability to fertilize or to be fertilized, and subsequently develop into a normal embryo. However, the quality of gametes can also be defined differently depending on the specific biotechnological applications that the gametes are to be used for, such as cryobanking, nuclear transfer or androgenesis. Several types of criteria can thus be used to quantitatively estimate egg and sperm quality; some of them being
Nutrition
Broodstock nutrition is an important factor susceptible to affect not only fecundity and gametogenesis but also gamete quality, and existing work has been extensively reviewed (Kjörsvik et al., 1990, Brooks et al., 1997, Izquierdo et al., 2001). It is well accepted in the literature that broodstock nutrition can significantly impact reproductive performance and this topic has been specifically reviewed by Izquierdo and co-workers (Izquierdo et al., 2001). The definition of reproductive
Conclusions and future directions
Egg quality can be defined as the ability of the egg to be fertilized and to subsequently develop into a normal embryo. Similarly, sperm quality can be defined as its ability to successfully fertilize an egg and subsequently allow the development of a normal embryo. The identification of predictive estimators or markers of gamete quality would have major applications in the field or in the industry. For eggs, it would help prevent the risk of mixing, for practical reasons, egg batches of poor
Acknowledgment
The authors thank Miranda Maybank for critical reading of the manuscript.
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