The development of a radioimmunoassay for carp, Cyprinus carpio, vitellogenin

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Abstract
The development of an easily — performed and robust radioimmunoassay (RIA) to carp, Cyprinus carpio, vitellogenin (c-VTG) is described. Purified c-VTG was iodinated using Iodogen. The resulting c-VTG label was useful for up to 60 days. High titre antibodies were raised in rabbits to the purified c-VTG. The practical operating range of the c-VTG RIA was between 2 and 200 ng. ml-1. VTG was detected in plasma from all female mirror carp investigated, and all plasmas diluted parallel to the standard. The plasma VTG level in female carp increased concomitantly with the GSI; levels increasing from the ng. ml-1 level in juveniles to a maximum of 1 mg. ml-1 in fully mature females. VTG level was a far more sensitive index of the degree of sexual development than was GSI. In males, blood levels of VTG were always undetectable. Vitellogenic plasma from all subspecies of C. carpio (e.g. mirror, common, Koi) diluted parallel to the standard, as did blood from most other female cyprinids, such as the roach (Rutilis rutilis), bream (Abramis brama), and dace (Leuciscus leuciscus), but not all. These results suggest that the structure of VTG is highly conserved within this family. However, plasma from vitellogenic salmonids did not cross-react in the RIA. The relationship between plasma VTG and calcium levels was studied in both carp and rainbow trout. In rainbow trout it was found that plasma calcium levels do not rise above basal levels until the VTG level exceeds about 1 mg. ml-1, and therefore in this species it is only useful as an indicator of the degree of ovarian development in the later stages of the reproductive cycle. In the carp, however, and probably other cyprinids, blood VTG levels do not appear to naturally exceed about 1 mg.ml-1, and plasma calcium levels are not suitable as an indirect measure of the VTG level.