Roland Billard

Bio: Roland Billard is an academic researcher from Institut national de la recherche agronomique. The author has contributed to research in topics: Sperm & Sperm motility. The author has an hindex of 53, co-authored 164 publications receiving 8927 citations.

7 The Gonadal Steroids

Abstract: Publisher Summary This chapter discusses that the gonads potentiality to produce steroids, and the regulation of the syntheses. The nature, shape, and intensity of a hormonal signal, ready to be received by a target cell, is the result of an intricate series of positive and negative regulations. In the case of hormonal steroids in fish, only some aspects of this complex have been considered. Once a steroid is secreted, several mechanisms may inactivate it before it reaches its target. Little is known of catabolism of sexual steroids in teleosts. Most available data are concerned with the total radioactivity found in tissues after fish are fed labeled steroid. The biological significance of glucuronidation or sulfonation remains to be explored. Although the conjugated steroids are usually considered to be inactive, recent studies attribute a pheromonal role to glucuronides. In other respects, the binding to plasma proteins may lead to a reversible inactivation, although, in mammals, it has been suggested that steroid secretion may be enhanced by the presence of serum steroid-binding proteins. Finally, the conversion of plasma steroids into biologically active metabolites can occur in some target tissues. The actual physiological role of gonadal steroids in fish is discussed with emphasis on gametogenesis.

Some problems related to the assessment of sperm motility in freshwater fish

Abstract: The motility of the spermatozoa of freshwater fish is usually of short duration, but a precise description has rarely been provided. Motility requires a high dilution (more than 1,000-fold) for initiation of synchronous motility in 100% of spermatozoa; a two-step procedure is necessary, with an initial dilution of 1 to 100 in a medium that keeps the spermatozoa immotile and allows good mixing of the viscous semen. The second dilution (1 to 20) in the activating solution can be made directly under the microscope. Studies of carp sperm indicate that movement of live sperm is influenced by the ionic environment. The inhibition of motility in semen is mainly due to K+ ions in trout and osmotic pressure in carp, but other ions such as Na+, H+, and Mg2+ also interfere. Initiation of motility in trout requires external divalent cations. Immediately after dilution at 20°C, spermatozoa exhibit large circular trajectories (>400 μm in diameter), high beat frequencies (60 Hz), and velocities of 250 μm/sec. These values decrease rapidly. Within 20 sec after dilution, most spermatozoa stop moving, although some of them show some agitation with low beat frequency (< 10 Hz) and with very limited displacement during the next few minutes. A similar pattern is observed in carp, with active motility lasting 40 sec. Under certain ionic conditions, intratesticular spermatozoa are motile and have some fertilizing capacity.

Spermatogenesis and spermatology of some teleost fish species

Abstract: In teleost fish, the whole of the processes involved in the formation of spermatozoa and their release and in fecundation are extremely diverse Two main types of testicular structure are distinguished : a tubular and a lobular Theorganization of the lobules and genital duct structure is very diverse in the latter type Spermatogenesis can be continuous, as in guppy, discontinuous with overlapping cycles, as in carp, or show well separated cycles as in trout Spermiogenesis shows increasing degrees of complexity, leading to the formation of extremely simple spermatozoa as in carp (spherical head, very little nuclear histone transformation, very simple mid-piece with untransformed cytoplasmic and mitochondrialremains) or much more complex spermatozoa as those of guppy (elongated head, histoneprotamine transformation, transformation of the centriolar complex in the deep nuclear notch, very developed mid-piece with glycogen stores) Spermatogenetic production is extremely variable (GSI : 01-10 % ; annual production : 1 $ 10 to 7 910 spermatozoa/g body weight) Spermiation yield varies according to species but also within the same species (20-90 % in trout) The endocrine model of spermatogenesis and spermiation is very different in carp and trout The main environmental factor influencing spermatogenesis is photoperiod in trout and temperature in carp ; spermiation depends on temperature in trout and on social environment as well as temperature in carp Sperm physiology (survival time in vivo and in vitro, motility time, metabolism) is very different in the several species studied Two groups with a fundamentally different physiology (internal or external fecundation), sperm biology and morphology (structure of testis and spermatozoon) can be grossly distinguished These groups are fish with lobular testes (guppy) and those with tubular testes (teleosts)

Cryopreservation of sperm in marine fish

Abstract: Since the first work of Blaxter in 1953, fish sperm cryopreservation has been attempted on about 30 marine species. The present paper reviews the techniques used and the results published in these species. Particular attention is paid to the handling procedure of sperm before freezing, the problems of semen ageing and semen contamination with urine. The quality of frozen-thawed semen was evaluated using previously standardized biotests, such as a two-step motility activation technique adapted for the different species and fertilization assays using a discriminating insemination technique. Most extenders used in marine fish are saline or sugar solutions. From the investigated cryoprotectants, dimethyl sulphoxide (DMSO) generally leads to the best results. Cooling rates range from 8 °C to 99 °C min-1; the thawing rate is generally high. Compared with freshwater species, a high percentage of spermatozoa survives cryopreservation. Therefore, and because of the simplicity of the techniques, the cryopreservation of marine fish sperm is suited for application in aquaculture.

Inhibition of testicular growth in rainbow trout (Oncorhynchus mykiss) exposed to estrogenic alkylphenolic chemicals

Abstract: It is becoming evident that an increasing number of widely used industrial and agricultural chemicals are estrogenic. The biodegradation products of a major group of nonionic surfactants, the alkylphenol polyethoxylates, are one such group. Some of these chemicals are widespread aquatic pollutants, and bioconcentrate in aquatic biota. Exposure of male rainbow trout (Oncorhynchus mykiss) to four different alkylphenolic chemicals caused synthesis of vitellogenin, a process normally dependent on endogenous estrogens, and a concomitant inhibition of testicular growth. The magnitude of these estrogenic effects was dependent on the estrogenic potency of the chemical, the stage of reproductive development of the fish, and the concentration of the chemical in the water. These results support the contention that exposure of wildlife to environmentally persistent estrogenic chemicals can result in deleterious reproductive consequences.

Pond aquaculture water quality management

Abstract: Preface. Selected Atomic Weights. Customary Metric Conversion Factors. 1. Water Quality and Aquaculture: Preliminary Considerations. 2. Ecology of Aquaculture Ponds. 3. Water Quality Requirements. 4. Water Use. 5. Liming. 6. Fertilization. 7. Aeration. 8. Water Circulation. 9. Turbidity and Appearance of Water. 10. Aquatic Weed Control. 11. Off-Flavors and Harmful Algae. 12. Pollution. 13. Chemical, Physical, and Biological Treatments. 14. Waste Management. 15. Measurement of Water Quality. 16. Sustainability and Environmental Issues. References. Index.