No description available.

Shortfin eels (Anguilla australis) and longfin eels (A. reinhardtii) are true freshwater eels of the genus Anguilla. There are many mysteries still unsolved for the freshwater eel lifecycle, such as location of the spawning grounds, conditions that promote metamorphosis from the leptocephalid to glass eel phase, and the mechanisms that affect glass eel recruitment. In Australia, little is also known about the estuarine habitats of glass eels as they migrate towards freshwater, and the age at which these eels enter estuaries. Both species are of commercial importance in the estuary fishery where they are caught in eel traps for export. There is also a small, but potentially lucrative, aquaculture industry for ongrowing glass eels to market demand size. This thesis investigates the spatial and temporal recruitment of both species of glass eels to estuaries within NSW, the habitats that may be of importance to them as they continue their upstream migration, and the age at which these eels entered the estuaries. Firstly, a new sampling device needed to be developed since conventional methods to catch glass eels often required constant observation of gear, multiple operators, specific physical site characteristics, and/or were expensive. The artificial habitat collectors that were developed were then used to sample six estuaries in NSW monthly within one week of the new moon. Shortfins showed a more consistent and defined recruitment across all sites than longfins, where the peak shortfin recruitment season was from April - August. Longfins recruited primarily from January - May but often recruited outside of this period. Five year collections at one of these sites provided important recruitment information. It appeared that longfins failed to recruit to this site during 2000/01, which could affect commercial catches of this species when they enter the fishery. The East Australian Current (EAC) probably transports glass eels from spawning sites in the Coral Sea southward to the east coast of Australia but there was no predicted lag time in the recruitment of eels from northern to southern estuaries. Therefore, it was not possible to predict the timing of recruitment of glass eels in one estuary based on the timing of recruitment in another more northern estuary. When glass eels enter estuaries their upstream migration is assisted by the night flood tide. During the ebb tide, glass eels burrow into the substrate and resurface at the next night flood tide. The eels do not select particular habitats at this time, rather, their location is dictated by the tide. However, once glass eels reach the estuarine/freshwater interface, they may prefer more complex habitats such as seagrass/macrophytes or rocks/cobbles in which to hide during the day. At this interface, glass eels undergo a physiological change to adapt to a freshwater existence and this change may take up to a few weeks. During this time, glass eels commonly enter the water column during the night flood tide and may be able to locate more suitable habitats in which to hide during the day. The ages of shortfin and longfin glass eels caught in estuaries were examined both spatially and temporally. As the EAC travels north to south, glass eels recruiting to the southern sites were expected to be older. However, shortfins that recruited to the northern-most site in this thesis were older than at all other sites while there was no difference in the ages of longfins. Also, when the ages of longfins that recruited during the main recruitment period were compared to the ages of longfins that recruited outside of this period, there was no difference in ages. Therefore, the hypothesis that these later recruiting eels may have been caught in an eddy prior to their estuarine arrival has been disproved. The ages of shortfins that recruited in two separate years were significantly different from each other and may be due to shortfins' ability to detrain more easily from the weaker currents that exist at these recruitment periods. Conversely, there was no difference in the ages of longfins that recruited in the same month during three separate years. The estimated hatch dates for shortfins was estimated at October to January, while for longfins, estimated hatch time was July to September for eels that recruited during the peak recruitment period. For longfins that recruited outside of the main recruitment period, estimated hatch times were from December to February. It is unknown, however, whether longfins have an extended spawning period, or whether silver eels arrived at the spawning grounds later and thus produced later arriving longfins. Continuous monitoring of glass eel recruitment to estuaries is necessary to determine whether there are long term declines in the recruitment of Australian eels similar to the declines recently observed for eels in Europe and Asia.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Zoology / Master / Master of Science

published_or_final_version / Zoology / Master / Master of Science

No description available.

No description available.

Calcium ion has diverse beneficial roles in living organisms. Failure in Ca2+ homeostasis affects a variety of molecular and cellular processes, ultimately leading to many pathological consequences. In mammals, body Ca2+ homeostasis is maintained by the coordinated calcium (re)absorption that occurs in the small intestines, kidneys and bones, and is under tight hormonal control. In fish, two special organs, Corpuscles of Stannius (CS) glands and gills form a regulatory circuit to detect and regulate blood Ca2+ homeostasis. However, the underlying molecular mechanism in the regulation of gill Ca2+ uptake has not been fully examined. Moreover, some putative biological active substances in CS glands have not been identified. To address these research questions, a euryhaline fish, Japanese eel (Anguilla japonica) was used as an animal model for the study. Fish gill is equipped with epithelial calcium channel (ECaCl) as gatekeeper of Ca2+ entry, and membrane Ca2+-ATPase (PMCA) for Ca2+ efflux. To test if branchial ECaCl and PMCA responded to change in water Ca2+ level, we investigated the changes in fish adapted in artificial freshwater (AFW), Ca2+-deficient AFW (D-AFW) or high Ca2+-AFW (H-AFW). Our data illustrated both short-term and long-term effects on modulations of the transporters. The changes correlated with expression levels of stanniocalcin-1 (STC-1) in CS glands. This part of study supports the regulatory circuit between gills and the glands. In primary cell culture of Japanese eel gill cells, Ca2+ sensing was shown to be mediated by Ca2+ sensing receptor (CaSR) coupled to phospholipase C (PLC)-extracellular signal-regulated kinase (ERK) and PLC-inositol triphosphate (IP3)-Ca2+/calmodulin-dependent protein kinase-II (CaMK-II) pathways. And CaSR-STC-1/cyclo-oxygenase-2 (COX-2) mediated protective pathway in gill cells that exerts a possible protective mechanism against an increase in intracellular Ca2+ levels associated with transepithelial Ca2+ transport. Apparently, the protective effects against Ca2+-mediated cytotoxicity of gill cell were mediated by STC-1 binding on gill cells that led to elevations of cytosolic cAMP. In a follow-up experiment of using Ca2+-imaging system in a model of thapsigargin (TG)-induced elevation of cytosolic Ca2+, a hypocalcemic action of STC-1 was demonstrated and was found to be mediated by cAMP and COX-2 pathway. To further determine the gene expressed in CS gland responsive to changes in water salinity, the first transcriptome database of CS glands from fish adapted in freshwater or seawater condition. A de novo assembly of RNA sequencing data generated 11747 unigenes and revealed 475 genes that were differentially expressed. Three functional clusters: (1) Ca2+-metabolism, (2) blood pressure and (3) ion-osmoregulation were revealed. Gene targets, in addition to STC-1 in related to the regulation of calcium metabolism and blood pressure, like calcitonin, atrial natriuretic peptide-converting enzyme and endothelin-converting enzyme 1 were identified. Taken together this thesis described a comprehensive study on the functional circuit between gills and CS glands to decipher the regulation and functions of transporters and hormones in calcium metabolism in fish.

Abstract There are 43 species of deep-sea eels of 8 families, which including 1 species of Chlopsidae, 2 species of Muraenidae, 3 species of Ophichthide, 14 species of Congridae, 2 species of Muraenesocidae, 2 species of Nemichthyidae, 2 species of Nettastomidae, and 15 species of Synaphobranchidae, which its depth from 150 to 1200 meters and distribution from NE coast to the coast of Taitong and SW coast in Taiwan waters. Meanwhile, there are 3 new species (i.e., Dysomma longirostrum, Ophichthus aphotistos, Synaphobranchus sinensis) and 11 new records (i.e., Chilorhinchus platyrhynchus, Ophisurus macrorhynchus, Rhechias retrotincta, Macroceohenchelys brachialis, M. soela, Japonoconger sivicolus, nettastoma solitarium, Meadia abyssale, Dysommina rugosa, Ilyophis brunneus, Synaphobranchus kaupi) are described. The study in this part also recognize vertebral formulae is useful of elucidating the difference among the species. Morphology of swimbladder, stomatch, gonads of the deep-sea eels and the melanin layer of diaphragm are able to be as a distinctive character to find out the relationship among the species and the families. Most eels¡¦ reproductive season concentrate on September to November, whatever, the synaphobranchids have two reproductive seasons, which are on May and September to October. And it should become important to make further research on the above phenomenon. True eels (anguilliforms) form a monophyletic taxon from 16 apomorphic characters, e.g., Well-developed olfactory bulbs, lateral-protruded telencephalon, large-sized tectum, a distinct gap between telencephalon and tectum, reduced neural arch, hamel arch, and uroneural, triangled urostyle, epural absent, convergent hypural, fused hypural 1-2 and hypural 3-4-5, gap between hypural 1-2 and parhypural, and a gap between hypural 1-2 and hypural 3-4-5. The present study also find (1) Muraenoidei and angulloidei are a sister ¡Vgroup by sharing a slit between telencephalon and tectum, smaller olfactory bulb and lobe, and slit on area posttrema; (2)Congroidei is a monophyletic group by sharing an oval tectum, large cerebellum, and ungrooved area postrema, fusion of hypural 3, 4, and 5; (3) Congroidea and Synaphobranchoidea share a fusion of parhypural with hypural 1 and a concave present between uroneural and hypural, which should be treated as a sister group; (4) most eels of Congridae share a FS-caudal-fin and should be treated as a clade; (5) Most eels of Ophichthidae share a reduced and degraded caudal-fin, which should be monoplyletic; (6) Synaphobranchinae¡BSimenchelyinae and Ilyophinae, uniquely sharing well¡Vdeveloped olfactory bulb, small telencephalon, lateral protrusion of telencephalon well developed, and cerebellum folded posteriorly, a CLC- caudal-fin and elevated hypural 3-4-5, and fusion of hypural 4 and 5, are belong to a monophyletic group; (7) a gap between parhypural and hypural 1 indicate Simenchelyinae and Ilyophinae should be treated as a sister group; (8) Eurypharynx, Cyema, and Monognathus sharing a reduced caudal fin and brain, which need further research to elucidate their relationship; (9) Dark-red saccus vasculosus appears to recommend a close relationship between Gavialiceps taeniola and duckbill eels. (10) A disc-like hypophysis suggests the eels, Albula, Pterothrissus, Notacanthus, Megalops, and Elops are closely related groups; (11) Albula, Pterothrissus, Megalops, and Elops share a distinct morphological type of tectum and cerebellum and they should be treated as closely related groups; (12) The brains¡¦ gross morphology of Albula, Pterothrissus, Megalops, and Elops are well developed, a correlation distinctly similar to that of the Clupea which need further study on the relationship among the taxa mentioned above and the Clupeiformes.

Thesis (M. Sc.)--University of Hong kong, 1973. / Typewritten.