Tools and triggers for eel reproduction

Freshwater eels (Anguilla spp.) intrigued scientists for centuries. Their life cycle involves for example two distinct larval stages and a long distance migration, which may cover thousands of kilometers. The farming of eels is still dependent on the influx of wild glass eels, because eels do not mature naturally in captivity due to strong neural inhibition. Since the 1980s, the glass eel influx of several eel species drastically declined. The European eel (A. anguilla) was recently enlisted by the IUCN as a critically endangered species; therefore there is an urgent call for eel management and artificial reproduction. Artificial reproduction may contribute to restoration of the eel population by releasing the current fishing pressures on the wild stocks, and allowing a sustainable eel aquaculture in the future. Although, artificial reproduction by applying hormone treatments is possible to some extent, success ra tes are still far from creating a sustainable aquaculture. This thesis focuses on the spawning migration, maturation and reproduction of eels. New tools are developed that may improve current artificial maturation and reproduction protocols for eel aquaculture.ZF-screens BV Passie voor Vis BV VOF van Vugt Transport ZuilichemUBL - phd migration 201

The map of chromosome 1 of man

Making maps is an essential procedure in the exploration of new territories. In the field of genetics, many basic concepts concerning the structure of a genome and the regulation of gene activity have emerged from regional mapping studies on the chromosomes of e.g. Escherichia coli and Drosophila melanogaster. The studies on Drosophila owe much of their significance to the suitability of this organism for correlation of data on gene linkage and gene expression with data on morphological and biochemical differentiation along chromosomes. Whereas chromosome mapping in Drosophila has a history of more than half a century, the history of regional mapping of human chromosomes covers slightly more than half a decade. The experimental approaches employed within that short period, although, show a striking diversity. This development was possible because several important techniques became available almost simultaneously

Ultrasonic imaging as a means of monitoring gonadal development in lumpfish (Cyclopterus lumpus)

The commercial farming of juvenile lumpfish requires monitoring of gonadal development to achieve synchronized production. Conventional methods such as gonadosomatic index (GSI), sex hormone analyses, gonadal histology, endoscopy, and gene expression analyses are costly, invasive, and often involve sacrificing the fish. We assessed the efficiency of ultrasound as a non-invasive method for monitoring gonadal development in lumpfish. Based on ultrasound observations, we categorized the fish into six stages; F0 to F5 for females and M0 to M5 for males, that represented maturity levels from immature to spent. Importantly, the ultrasound gonadal stages aligned with histological gonadal stages. Additionally, ultrasound stages aligned with profiles of GSI, testosterone (T), 11-ketotestosterone, and 17β-estradiol throughout gonadal development including the spawning period. Moreover, these parameters exhibited significant positive correlations with each other reflecting their parallel trends during gonadal development. To minimize the frequency of ultrasound usage and fish handling, we established F3 and M3/M4 as arbitrary thresholds for identifying ripe females and males, respectively. By using these thresholds, the need for regular ultrasound monitoring could be reduced during most of the rearing period. Ultrasound proves to be useful and reliable for monitoring gonadal development in lumpfish, enabling synchronized production of juvenile fish

The Effect of Drag and Attachment Site of External Tags on Swimming Eels: Experimental Quantification and Evaluation Tool

Animal science

Comparison of swimming capacity and energetics of migratory European eel (Anguilla anguilla) and New Zealand short-finned eel (A-australis)

Animal science

Effects of weathered polyethylene microplastic ingestion on sexual maturation, fecundity and egg quality in maturing broodstock Atlantic cod Gadus morhua

Microplastics (MPs) have become a global issue as they are omnipresent in the ocean. Fish ingesting MPs through feed could be affected in their physiological function, e.g., disrupted enzyme production and function, reduction of feeding and reproductive failure. This study assessed the effects of feed containing naturally weathered MPs from the Oslofjord (Norway) on the reproductive physiology of Atlantic cod (Gadus morhua). Farmed cod broodstock were fed either control (C-diet) or feeds containing 1% microplastic (MP-diet) starting nine months prior to spawning, from June until May. No major differences were found between diet groups in overall biometrics or gonad histology. Sex steroid levels (testosterone, 11-ketotestosterone and 17β-estradiol) resulted in expected profiles increasing over time without any significant differences between treatments. Gene expression levels of the steroidogenic enzyme 20β-hydroxysteroid dehydrogenase (20β-hsd) and vitellogenin1 (vtg1) showed significant differences between dietary treatments with lower expression in the control group. This can be a direct effect of MPs, but endocrine disrupting effects of potentially leachable plastic additives cannot be completely ruled out. Thus, these enzymes could be indicators of exposure to contaminants that disrupt sexual maturation by affecting the production of primarily maturation-inducing steroid. Although the concentration of MPs employed in this study may not be high enough to elicit any observable short-term biological effects, the observed gene expression suggests that long-term consequences should be considered caused by an expected increase of MPs in marine environments