Sex, pheromone and aggression in Norway lobster (Nephrops norvegicus) : for a better future of scampi
Thesis or dissertation
- © 2011 Emi Katoh. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
With a steadily increasing world population the demand for seafood has been growing rapidly over the past century. This has led to overfishing and decreasing catch rates in many seafood species. High fishing activity has endangered several aquatic species and pushed others to extinction. Signs of high fishing activity were also found in the Nephrops. In order to secure sustainability of important seafood species such as the Norway lobster (Nephrops norvegicus) it is important to intensify the research efforts on these species. Aggressive behaviour and injury are major constraints of communal holding of aquatic animals. A good knowledge of reproductive behaviour and larvae development is important for any hatching programs. Therefore, the aim of this thesis was to provide a research base that can improve sustainability of Nephrops and their well being in captivity, in order to culture them.
Both male and female Nephrops show fighting behaviour. However, only in fights with males a clear dominance relationship was maintained. Males and females recognise the higher status of their male opponent. Blocking of urine release showed that chemical communication by urinary signals is important in maintaining dominance relationships between males.
When comparing communal holding conditions to individual holding conditions over one months, no difference in death rate was found, indicating that a stable dominance hierarchy reduced aggression between animals that were kept in communal tanks. Although females lack the ability of recognising dominance in other females, they do recognise dominance in males. Male Nephrops have larger claws compared to the females showing additional sexual dimorphisms in the species. Moreover, Nephrops with larger claws tend to win the fights showing that claw size affects the outcome of fights.
In lobsters, mating usually occurs after the female has moulted, and is in the soft shell condition. In Nephrops the highest number of matings occurred when the females were in the soft shell (postmoult) stage, but many males also tried to mate with a hard shelled (intermoult) female when the odour of a soft shell female was present. This indicates that soft shelled female odour has an important effect on male behaviour. Similar to European lobsters (Homarus gammarus) and American lobsters (Homarus americanus), some Nephrops males also mate with hard shelled females even if no chemical cues from soft females are present. Thus, intermoult mating indicates the presence of female sex pheromone beyond the post moult stage.
This thesis provides applicable information to improve the Nephrops fishing industry and gives further details to enable Nephrops culturing in the future.
- Department of Biological Sciences, The University of Hull
- Breithaupt, Thomas; Johnson, Magnus
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