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GENERAL DISCUSSION 1. Improvements to the control of European eel reproduction The control of the reproduction of the European eel has become the focus of much research due to the severe decline in the natural stocks. Nowadays breeding in captivity seems to be the only alternative both in order to reduce the pressure on natural populations and to meet the demands of the eel farms (Feunteun, 2002). In a breeding captivity program, the first step is to achieve high quality gametes in order to reach high fertilization and hatching rates (Bozkurt et al., 2006). During this thesis, alternative treatments for the induction of maturation were carried out with the aim of improving several male reproductive traits in the European eel such as the onset and the duration of the spermiation period and the quantity and quality of sperm (see Chapter 2). The most used method until now in this species, which involves the weekly injection of hCG (1.5 IU g -1 fish) under a constant thermal regime of 20 ºC (Pérez et al., 2000), has previously shown successful spermiation results in closely related species such as the Japanese eel (Anguilla japonica; Ohta el al., 1997), American eel (Anguilla rostrata; Sorensen and Winn, 1984) or New Zealand eel (Anguilla australis; Todd, 1981), thus that treatment is able to induce in an effective way both spermatogenesis and spermiogenesis in eel species. The results obtained in this study using this standard treatment agree with previously published reproductive data on European eel such as the onset of spermiation, the percentage of spermiating males or sperm volume (Asturiano et al., 2005; Pérez et al., 2000). However, the total motility values from our experiment (described in Chapter 2) were much higher than those obtained in previous studies where an identical maturation method had been applied. In this respect, numerous factors such as i) the variability between eel batches, ii) the hormone provider, and especially iii) the way of evaluating the sperm samples (subjective against objective methods) could explain these differences. Nowadays, thanks to the use of an objective and accurate previously standardized CASA system (see 125
GENERAL DISCUSSION Chapter 1), the way of evaluating the sperm samples does not handicap the assessment of the sperm quality, meaning it is possible to compare a wide range of aquacultural matters in a more effective and accurate way. The water temperature, which plays an important role in the sexual maturation of several fish species, was chosen as the first factor to improve the reproductive performance of male European eels. Our results demonstrate that the onset and progression of spermiation were strongly influenced, and probably closely regulated, by changing water temperature. However, the alternative treatments tested in this study (T10 and T15) did not improve the results of the samples induced by the constant regime (T20), and a greater number of weeks were necessary in the alternative treatments both to induce the onset of spermiation and to achieve high quality sperm samples. Therefore, a constant temperature of 20 ºC is recommended in order to achieve the best spermiation performance during induced maturation of male European eels. Nevertheless, it is necessary to highlight that when we talk about “best results”, we do so from an aquaculture point of view, trying to get spermiating males and high quality sperm weeks in advance. From a biological viewpoint, we observed that treatments T10 and T15 were also able to induce both a high percentage of spermiating males and high quality samples, but several weeks later. The warm temperatures during these alternative treatments (T10 and T15) were strictly imperitive in inducing final sperm production, thus this fact could indicate that gonadal development in eel males could be slowed down by the cold waters they encounter before arriving at the warm Sargasso Sea, and then relaunched once there in order to synchronize gamete maturation and the fertilization of the eggs produced from the females. In fact, it has been reported that variable thermal regimes in both European and Japanese eel females induce hormonal profiles that more closely resemble the natural ones than those obtained under constant temperatures (Dou et al., 2008; Pérez et al., 2011). Therefore hormonal data from male eels undergoing variable thermal regimes are being estimated in order to evaluate the hormonal 126
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SPERM PHYSIOLOGY AND QUALITY IN TWO
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ACKNOWLEDGEMENTS Muchos años han p
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aunque tiene una alcachofa en la ca
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TABLE OF CONTENTS SUMMARY 1 RESUMEN
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SUMMARY SUMMARY The conservation st
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RESUMEN RESUMEN Las especies objeto
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RESUM RESUM Les espècies objecte d
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GENERAL INTRODUCTION 7
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GENERAL INTRODUCTION who postulated
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GENERAL INTRODUCTION 2. Sperm physi
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GENERAL INTRODUCTION Finally, the a
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GENERAL INTRODUCTION 3. Sperm quali
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GENERAL INTRODUCTION in fish (Kime
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GENERAL INTRODUCTION However, for s
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GENERAL INTRODUCTION future applica
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GENERAL INTRODUCTION With regards t
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OBJECTIVES The chapters presented b
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STANDARDIZATION OF SPERM MOTILITY E
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CHAPTER 2 Study of the effects of t
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CHAPTER 2 reducing the pressure on
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CHAPTER 2 ongoing task in order to
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CHAPTER 2 To measure sperm density,
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CHAPTER 2 Spermiating males (%) 100
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CHAPTER 2 100 80 60 I II III IV A 4
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CHAPTER 2 3.2 Hormonal treatments P
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CHAPTER 2 With regard to the sperm
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CHAPTER 2 Relative volume (%) 80 I
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CHAPTER 2 In this respect, it is we
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CHAPTER 2 treatment to that of the
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CHAPTER 2 Our results demonstrate t
Page 82 and 83: ROLE OF IONS IN THE SPERM ACTIVATIO
Page 92: CHAPTER 4 Study of pufferfish (Taki
Page 95 and 96: CHAPTER 4 2002) so Takifugu niphobl
Page 97 and 98: CHAPTER 4 carrying out sperm collec
Page 99 and 100: CHAPTER 4 Table 1. Activation media
Page 101 and 102: CHAPTER 4 TM (%) 100 A a a Und-PD a
Page 103 and 104: CHAPTER 4 TM (%) 80 60 40 20 0 A a
Page 105 and 106: CHAPTER 4 TM (%) 80 A ASW100 GLU 60
Page 107 and 108: CHAPTER 4 although the activation m
Page 109 and 110: CHAPTER 4 dilution ratio and an opt
Page 111 and 112: CHAPTER 4 2006). Several studies in
Page 113 and 114: CHAPTER 4 5. Conclusions Some concl
Page 116 and 117: RELATIONSHIP BETWEEN SPERM MOTILIY
Page 130: RELATIONSHIP BETWEEN SPERM MOTILIY
Page 136 and 137: GENERAL DISCUSSION profiles induced
Page 138 and 139: GENERAL DISCUSSION more studies on
Page 140 and 141: GENERAL DISCUSSION sperm motility p
Page 142: CONCLUSIONS 133
Page 145 and 146: CONCLUSIONS vii. The coefficients o
Page 148 and 149: REFERENCES Aarestrup K, Økland F,
Page 150 and 151: REFERENCES Beirão J, Cabrita E, P
Page 152 and 153: REFERENCES Cabrita E, Robles V, Cu
Page 154 and 155: REFERENCES De Vos A, Van De Velde H
Page 156 and 157: REFERENCES Gallego V, Pérez L, Ast
Page 158 and 159: REFERENCES sperm competition and fe
Page 160 and 161: REFERENCES Liu QH, Li J, Xiao ZZ, D
Page 162 and 163: REFERENCES Mortimer ST. Effect of i
Page 164 and 165: REFERENCES Peñaranda DS, Marco-Jim
Page 166 and 167: REFERENCES Rurangwa E, Volckaert FA
Page 168 and 169: REFERENCES Tesch F. Telemetric obse
Page 170 and 171: REFERENCES Wong PYD, Lee WM, Tsang
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