In the economically important Mediterranean swordfish trade, the determination of sex and gonadal maturity at capture are important requisites for regulation. These parameters cannot always be resolved by inspection during gutting at sea, lack of external sexual dimorphism or high market muscle value precluding gutting. The objective of this study is to develop a more efficient, cost-effective assessment method for determining sex and gonadal maturity, using an ELISA mediated muscle biopsy assay to measure the levels of sex hormones and the lipoprotein vitellogenin from swordfish muscle samples. These substances can be used as indicators of sex and spawning state of the fish and correlated with gonadal development. The new muscle biopsy method would be relevant for other marine species, providing a valuable management tool to oversee conservation measures in the market place in terms of species, sex and gonadal maturity from single muscle samples.
The objectives of this project are:
1) to identify and isolate sex hormones and vitellogenin in the plasma and muscle biopsy samples taken from swordfish
2) to develop an ELISA-mediated standard test tool to determine the concentrations of the above substances in both plasma and muscle
3) to verify the correlation between hormone and vitellogenin levels in both plasma and muscle biopsy samples with biometric data on gonadal indices and sex ratio
4) to test and evaluate muscle biopsy in both field (double blind) and market conditions
5) to provide a standard muscle biopsy method for assessing sex ratio and gonadal maturity for marine fisheries in the Mediterranean.
Progress to Date
All the work has been completed.
The high percentage of swordfish landed intact in Spain gave the sampling programme severe difficulties, despite extensive efforts by the partners, and emphasised again the need for a blood or muscle biopsy. A large proportion of the Spanish catch was less than 120 cm; females of this size are not fully mature and males may show extremely limited reproductive ability. The histological study of swordfish ovaries allowed the identification and characterisation of four main developmental stages of oocytes. Based on the type of oocytes present in the ovaries and the presence of post-ovulatory follicles, a six-stage scale of ovarian development has been set up and all the ovary samples collected in the three areas under investigation have been classified accordingly. Hepatic tissue from both male and females studied showed evidence of VTG production and various morphological abnormalities. The results of this study may increase concern regarding the damage caused by accumulation of toxic compounds in top predator organisms living in the Mediterranean. Such effects may be particularly important to the future of commercial fisheries of already over-fished populations if they lead to decreased fertility. In addition, it raises a question about the risk to human health from the consumption of fish containing bio-accumulated endocrine disrupters. There was no relationship between plasma and muscle values, with one exception, estradiol (2001). It was concluded that it is not possible to use steroid concentrations in muscle tissue of the swordfish as a means of determining the sexual status of this species. It is generally assumed that GSI is a good measure of sexual development but our data showed no correlation between GSI and steroid concentration. The pattern of steroids in the swordfish is similar to that of other teleosts with higher 11-ketotestosterone in males and higher estradiol in females. Testosterone did not show any correlation with sex or maturity. In general terms high 11-ketotestosterone was correlated with male fish and high estradiol with females, which is in accordance with expectations, and the basis of this proposal.
FISHERIES AND AQUACULTURE
Scientist responsible for the project
Professor CHRISTOPHER ROBERT BRIDGES
Germany - DE
Phone: +49 2118 114991
Fax: +49 2118 114991