Les lignées clonales sont un outil puissant pour une meilleure caractérisation génétique des organismes utilisés en recherche. En utilisant les techniques de reproduction uniparentale, de telles lignées peuvent être développées chez les poissons en seulement deux générations. L'androgenèse avait déjà été réalisée chez plusieurs espèces d'eau douce et a été tentée chez le loup, une espèce d'intérêt économique et scientifique. Le faible nombre d'individus contenant effectivement uniquement le patrimoine génétique du père, après irradiation des œufs aux UV, a soulevé des questions quant à la présence de composés photoprotecteurs dans les œufs pélagiques. Les acides aminés de type mycosporines et le gadusol ont été recensés dans de nombreux organismes marins et d'eau douce, mais leur présence n'a pu être reliée au comportement flottant ou coulant des œufs. Tandis que le gadusol apparaissait en plus grande quantité dans les œufs marins flottants, ce résultat était beaucoup moins clair en eau douce et le type de composés photoprotecteurs semble lié à la phylogénie. D'autres études sur les mécanismes de photoréparation de l'ADN pourraient éclairer les résultats obtenus dans les expériences d'androgenèse. La gynogenèse avait déjà été reportée chez le loup mais le grand nombre d'individus méiotiques contaminant les descendances homozygotes produites a conduit à valider des marqueurs microsatellites efficaces à distinguer les individus mitotiques. De plus, un retard de développement des gonades a été observé, augmentant les difficultés à obtenir les lignées clonales. La grande variabilité observée entre les individus quant au succès des reproductions uniparentales a montré que la caractérisation et la qualité des gamètes sont un préalable indispensable. / Clonal lines are a powerful scientific tool for improved genetic characterization of organisms used in research. Inbred fish lines can be produced in only two generations using uniparental reproduction techniques. Androgenesis, achieved with variable success in several freshwater species, has been attempted in the European sea bass (Dicentrarchus labrax L), a marine fish of commercial and scientific interest. The low yields of progenies inheriting only the paternal genome after UV-irradiation of eggs led to considerations on the occurrence of UV screening compounds in pelagic eggs. Mycosporine-like amino acids and gadusol were found in many marine and freshwater organisms, but their occurrence in fish eggs was not clearly related to a behavioral pattern and while gadusol appeared in higher proportions in pelagic marine eggs compared to benthic species, this statement did not apply in freshwater, and moreover the kind of compounds was related to phylogeny. Further studies on DNA photorepair could enlighten hypotheses to understand the mechanisms underlying the disparate results obtained in inducing androgenesis in different fish species. Gynogenesis was reported successful to produce clonal founders in the sea bass, but high numbers of meiotic individuals contaminating fully homozygous progenies highlighted the need for efficient DNA markers to distinguish mitotic gynogenetic individuals. Furthermore, gonad development was highly delayed in gynogenetic progenies enhancing the difficulties to produce clonal lines. A high variability between individuals in the success of uniparental reproduction brought out gamete characterization and quality as a prerequisite.

Ultraviolet light is damaging but fish have evolved protective mechanisms, which allows them to live in shallow water reefs, high in UV radiation. This thesis details my investigation into the physiological ecology of solar ultraviolet (UV) absorbing compounds, known as mycosporine-like amino acids found in the external epithelial mucus, and examines the supporting role potentially played by a UV-induced DNA repair mechanism in coral reef fish of the Indo-Pacific. Using reverse phase chromatography and UV spectrophotometry, I examined whether the distribution of MAA compounds across different areas of the body is correlated with differential UV exposure. Comparisons were made between the MAA content and the absorbance spectra of mucus from the dorsal, ventral, caudal and head body surface areas in five species of Scaridae (Chlorurus sordidus, Scarus schlegeli, S. niger, S. psittacus and S. globiceps) from Ningaloo Reef, Coral Bay, Western Australia. All fish analysed had at least five MAAs present, and results showed that fish had increased UV absorbance in mucus over the dorsal area, which receives the brunt of UV radiation. Little UV protection was found in mucus from the ventral area, which receives the lower level of UV radiation mostly via reflection of the sand and reef surfaces. Furthermore, UV absorbance per mg dry mucus versus standard fish length showed that there is a positive relationship in C. sordidus with increasing size. I examined whether there is a difference in the quantity of UV screening compounds found in the mucus of fish along a longitudinal geographical gradient from inshore reefs (Lizard Island, Great Barrier Reef) to the outer edge reefs to oceanic reefs (Osprey Reef). MAA absorbance increased with longitudinal distance from the mainland landmass of Australia to more oligotrophic outer reefs, where UV attenuation is reduced and the ocean is more transparent to UV wavelength. I determined that fish living on inshore, more turbid reefs where UV attenuation in shallow waters is high have lower levels of MAA protection than fish from clear oceanic reefs. Furthermore, there seems to be a direct relationship between light attenuation and exposure with the quantity of protective sunscreening found in the mucus of reef fish. It is know that UV irradiation decreases with water depth and that mucus from fish with deep habitats absorbs less UV than that of fish from shallow habitats. It is unknown however, whether this UV protection is variable within the same individuals and if so, how fast changes 11 occur. To test this, I relocated 9 ambon damselfish from a deep reef (18 m) to a shallow reef (1.5 m) to expose fish to increased levels of UV and relocated another 7 fish from a shallow to a deep reef to expose fish to decreased levels of UV. One week after relocation, all fish were returned to their original reef site to determine whether MAA levels would return to their initial levels. Fish relocated to a shallower depth were recovered and had a 60% (SD+/-2%) increase in mucus UV absorbance. Conversely, the fish relocated to a deeper depth were recovered and had a 41% (SD+/-1%) decrease mucus UV absorbance. No difference was found between UV absorbance of relocated and original fish at both depth. Six days after fish were returned to their original reef, mucus UV absorbance levels had returned to 67% +/- 4% of the original level. These results show that mucus UV absorbance is variable in individual ambon damselfish and that the sunscreen protection typical for a certain depth is reached in relocated fish within just a few days of relocation. The rate of MAA loss is higher than the accumulation of MAAs suggesting that diet is not the sole determining factor involved in the sequestration of MAAs to mucus. The cleaner fish Labroides dimidiatus performs a mutualistic service by removing ectoparasites such as gnathiid isopods as well other dead infected tissue from its clients. Cleaner fish however are also known to feed on client mucus. The benefits of eating mucus until recently were unclear. In this study, we analysed the mucus of several cleaner fish clients to determine whether mucus feeding has a nutritional advantage over gnathiids and whether cleaner fish obtain their own MAA protection through this dietary mucus ingestion. Results show that host fish that are infected with gnathiids of poor nutritional value, in contrast to those that harbour gnathiids with higher nutritional value, continuously exude mucus that has both high nutritional value and high MAA content. These findings support the conclusion that in a competitive market for cleaners some host fish are forced to offer more than parasites to cleaners. Ultraviolet light that is not filtered by UV absorbing compounds such as MAA may still lead to DNA damage such as the formation of cyclobutane pyrimidine dimers (CPDs) or 6-4 photoproducts (6-4 PPs). However, coral reef fish have alternative mechanisms to overcome UV induced damage via the photolyase DNA repair mechanisms. We experimentally demonstrated for the first time that a coral reef fish species, the moon wrasse Thalassoma lunare has the ability to repair DNA damage via photoreactivation. Fish both with and without MAA protection were irradiated with UVB wavelength to induce DNA lesions. Half of the experimental fish were then exposed to photoreactivating wavelength to induce DNA repair 12 while the other fish were blocked from the repair mechanisms. Fish which had undergone DNA repair had the lowest number of lesions regardless of mucus MAA protection. When fish were blocked from photoreactivation wavelengths MAA sunscreens clearly served a photoprotective role. The amount of damage was greatest in fish which both lacked MAAs and which were also blocked from photoreactivating wavelengths. Thus for the overall UV protection of fish both the MAA sunscreens as well as the DNA repair system play a significant role in counteracting UV damage. Ultraviolet protection by MAA sunscreens is ubiquitous in marine fish. To date the same 5 MAA compounds (palythine (λmax 320 nm), asterina (λmax 330 nm), palythinol (λmax 332 nm), usujirene (λmax 357 nm) and palythene (λmax 360nm) have been identified in the mucus of several different species of reef fish from Australia. Here we report the first evidence of the presence of additional UV absorbing compounds found in the mucus of fish from Indonesia. Using UV spectroscopy the mucus of four species of fish was compared between both geographical regions. The presence of an additional peak between 294-296 nm wavelengths suggests the presence of gadusol and/or deoxygadusol, which are photoprotective compounds, thought to be the precursors of MAAs. Thus, UV protecting compounds in the mucus of fish may not be as conserved between different regions as previously assumed. Our knowledge concerning the effect of UV radiation has advanced considerably in the past decade and my research findings contribute to the better understanding of protective mechanisms of marine fish. The correlations I have found between UV attenuation/exposure, depth, and longitude of sampled individuals lead me to believe that mucus UV absorbing MAA compounds are a highly efficient adaptive defence.