Publication Abstract

Production, release and olfactory detection of sex steroids by the tench (Tinca tinca L.)

M.L.Pinillos, A.J. Guijarro, M.J. Delgado, Hubbard, P.C., Canario, A.V.M. and A.P. Scott

The present study is concerned with pheromone communication in tench (Tinca tinca L.), establishing firstly whether males had a high olfactory sensitivity to some typical teleost sex steroids and prostaglandins; and secondly whether males and females might be able to synthesise and release some of these steroids into the water. The C21 steroid, 17,20β­dihydroxy-4-pregnen-3-one (17,20β-P) was found to give large electro-olfactogram responses with an estimated threshold of detection of 10^-12 M. The male tench were equally sensitive to glucuronidated 17,20β-P (10^-11.6 M) but 100 times less sensitive to sulphated 17,20β-P (11^-9.7 M). Preliminary data from cross-adaptation studies suggest that both the free and conjugated forms are detected by the same olfactory receptor(s). Male tench also had high olfactory sensitivity to prostaglandin F2_α, (PGF2_α) and 15-keto PGF_2a (11^-11.5 and 10^-11.4 M). They were relatively insensitive, however, to testosterone (T), androstenedione (AD), 11-ketotestosterone (11-KT), 17β-oestradiol (EZ), 17,20β,21-trihydroxy-4-pregnen­3-one (17,20β,21-P) and 17,20α-dihydroxy-4-pregnen-3-one (17,20α-P).

Radioimmunoassays were used to measure the steroids in plasma and water and all samples were processed for the measurement of free, sulphated and glucuronidated fractions. In females, free 17,20β-P, 17,20α-P, T and AD in plasma showed the largest increases in response to injection with mammalian gonadotropin-releasing hormone analogue (GnRHa) or Ovaprim (a mixture of GnRHa and a dopamine inhibitor). Free 17,20β-P and 17,20α-P were also released into the water at the greatest rate. Plasma concentrations of the two conjugated forms of 17,20β-P were also elevated 18 h after the administration of GnRHa, but not by as much as the free steroid. In males, AD and 11-KT showed the greatest increase in response to GnRHa and were moreover released into the water at a higher rate in the treated group than in the control. The data support a possible pheromonal role for free and glucuronidated 17,20β-P.

Reference:

M.L.Pinillos, A.J. Guijarro, M.J. Delgado, Hubbard, P.C., Canario, A.V.M. and A.P. Scott. 2003. Production, release and olfactory detection of sex steroids by the tench (Tinca tinca L.) Fish Physiology and Biochemistry 26: 197-210