Browsing by Author "Scott, A. P."
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- Evidence for involvement of chemical communication in reproduction of the eel Anguilla anguillaPublication . Huertas, Mar; Hubbard, Peter; Scott, A. P.; Canario, Adelino V. M.; Cerda, J.The European eel (Anguilla anguilla) is characterised by long transoceanic migration to spawning sites during which the fish become sexually mature. A previous study demonstrated that mature eels may induce physiological and behavioural changes in immature conspecifics. This raises the possibility that chemical communication may be involved in this process. The aim of the current study was, therefore, to assess the olfactory sensitivity of eels to conspecific-derived odours and to establish whether these odours differ according to sex and/or state of maturity.
- Plasma concentrations of ovarian steroids in relation to oocyte final maturation and ovulation in female plaice sampled at seaPublication . Scott, A. P.; Witthames, P. R.; Turner, R. J.; Canario, Adelino V. M.Blood plasma concentrations of free 17â-oestradiol, free testosterone and glucuronidated testosterone were strongly positively related to the percentage of vitellogenic oocytes remaining in the ovaries of plaice Pleuronectes platessa caught at sea—being at their highest in pre-spawning (stage IV) females (i.e. those in which the oocytes were close to fully grown, but had not yet entered the stage of final maturation). In contrast, the concentrations of free and sulphated 17,20â-P, 3á,17,20â-P-5â, and 3á,17,21-P-5â were at their lowest in stage IV females. Free 17,20â-P (the putative maturation-inducing steroid) became only slightly elevated (less than twofold) during spawning (i.e. in stage V and VI females with hydrated and/or ovulated eggs). Sulphated 17,20â-P and 3á,17,21-P-5â became slightly more elevated (three- to fourfold). However, sulphated 3á,17,20â-P-5â concentrations increased 30-fold and were at their highest in fish in which only 40% of vitellogenic oocytes remained in the ovaries. Sulphated 17,20â-P, 3á,17,20â-P-5â and 3á,17,21-P-5â concentrations were significantly positively related to hyaline oocyte batch size; and sulphated 17,20â-P and sulphated 3á,17,20â-P-5â were significantly negatively related to the degree of hydration of the hyaline oocytes. None of the steroid concentrations, however, was related to the time of capture. More ovulated females were found in the afternoon than at any other time of the day.
- Production, release and olfactory detection of sex steroids by the tench (Tinca tinca L.)Publication . Pinillos, M. L.; Guijarro, A. I.; Delgado, M. J.; Hubbard, Peter; Canario, Adelino V. M.; Scott, A. P.The present study is concerned with pheromone communication in tench (Tinca tinca L.), establishing firstly whethermales have 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, 17,20β-dihydroxy-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 F2α (PGF2α) and 15-keto PGF2α (11−11.5 and 10−11.4 M). They were relatively insensitive, however, to testosterone (T), androstenedione (AD), 11-ketotestosterone (11-KT), 17β-oestradiol (E2), 17,20β,21-trihydroxy-4-pregnen-3-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 themeasurement of free, sulphated and glucuronidated fractions. In females, free 17,20β-P, 17,20α-P, free and glucuronidated 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 was 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.
- Sexually mature European eels (Anguilla anguilla L.) stimulate gonadal development of neighbouring males: possible involvement of chemical communicationPublication . Huertas, Mar; Scott, A. P.; Hubbard, Peter; Canario, Adelino V. M.; Cerda, J.This study was aimed to investigate whether sexual maturation of immature male eels could be stimulated indirectly by placing them in contact with either male (Minj) or female (Finj) eels in which sexual maturation had been stimulated directly by weekly injections of human chorionic gonadotropin (hCG) or salmon pituitary extract (SPE), respectively. Untreated males were placed either in the same tank or in a separate tank that was linked to the injected Wsh via a recirculation system. The hormonal treatments stimulated spermatogenesis and spermiation in Minj, and ovulation in Finj as well as an increase of the ocular (Io) and gonadosomatic (GSI) indices in both sexes. Plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) increased in Minj and T and 17 -estradiol (E2) in Finj. A small peak of plasma 17,20 -dihydroxypregn-4-en-3-one (17,20 P) occurred during ovulation, while the plasma levels of 17 -hydroxypregn-4- ene-3,20-dione (17P) were undetectable in both males and females. The water conditioned by Minj and Finj induced signiWcant, though relatively minor, increases in Io and GSI in uninjected males. In addition, uninjected Wsh showed small changes in plasma T and 11-KT levels, apparently related to the timing of spermiation and ovulation of Minj and Finj, respectively, as well as an activation of spermatogenesis (but not spermiation). Injected Wsh released free and conjugated T, 11-KT and E2 into the water, although immature eels were unable to smell (by electro-olfactogram) any of these steroids or prostaglandin F2 . However, immature males were highly sensitive to water extracts conditioned by spermiating Minj and pre-ovulatory and ovulated Finj. These preliminary results suggest the existence of chemical communication between maturing eels and immature males that stimulates gonad development, although the putative pheromone(s) involved has/have not yet been identiWed.