In an accompanying paper we report that herring milt contains high concentrations of conjugated cortisol and 17α,20β-dihydroxy-4-pregnen-3-one. We suggest that one source of these steroids was the urine, which could have become mixed with the milt during the hand-stripping procedure. In the present study, samples of hand-stripped milt from several other species, plaice (Pleuronectes platessa), dab (Limanda limanda), flounder (Platichthys flesus), goldfish (Carassius auratus), and rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri), were assayed for free and conjugated cortisol. Uncontaminated samples of plasma, seminal fluid, and urine of male herring and plaice were also assayed for free and conjugated cortisol (both species), 17α,20β-dihydroxy-4-pregnen-3-one (herring only), 17α,20α-dihydroxy-4-pregnen-3-one, and 3α,17α,21-trihydroxy-5β-pregnan-20-one (plaice only). The results showed that hand-stripped milt from these other species, excluding rainbow trout (from which it was possible to obtain urine-free milt), also had markedly high levels of conjugated cortisol (200–1000 ng∙mL−1). Urine of herring and plaice had particularly high levels of conjugated cortisol (ca. 5 μg∙mL−1). Uncontaminated seminal fluid from herring, but not from plaice, also had high levels of conjugated cortisol (ca. 2 μg∙mL−1). Urine and plasma, but not seminal fluid, of herring had elevated levels of conjugated 17α,20β-dihydroxy-4-pregnen-3-one. Urine, but not plasma or seminal fluid, of male plaice had elevated levels of 17α,20α -dihydroxy-4-pregnen-3-one and 3α,17α,21-trihydroxy-5β-pregnan-20-one. It would appear that fish urine is a rich source of conjugated steroids and that care must be taken, when collecting milt for pheromone studies, to avoid urine contamination.
The Distribution of 35S-Sulfadiazine and 14G-Trimethoprim in Rainbow Trout, Salmo Gairdneri
