Water temperature and pH influence olfactory sensitivity to pre-ovulatory and post-ovulatory ovarian pheromones in male Barilius bendelisis.

The attractive response and sexual activity elicited by pre-ovulatory steroid sulphate and post-ovulatory 15K-PGF pheromones are greater in wild caught tubercular males and immature males which express breeding tubercles on the snout (at 12-13 days post androgen implant) than in non-tubercular and non-androgen implanted males of freshwater fish Barilius bendelisis. This shows that circulatory androgens exert an activational effect on olfactory receptors of male fish. Wild caught tubercular males and androgen implanted juvenile males exhibit a high responsiveness to steroid sulphate at the water temperature and pH which fish experience during the pre-spawning phase. The male's sensitivity to 15K-PGF is almost equally high at the water temperature and pH which they experience in wild during the both pre-spawning and spawning periods. This suggests that the differential olfactory sensitivity to the two classes of pheromones in androgen implanted males is due to the varied temperature and pH of water, and that during the breeding season the male's olfactory sensitivity to PGF pheromone is more widespread than to the steroidal pheromone. An increased and decreased olfactory sensitivity in mature males to sex pheromones and L-alanine respectively during the breeding phase is in agreement with the hypothesis that pheromonal stimuli dominate over feeding stimuli to promote spawning success.

Ovarian steroid sulphate functions as priming pheromone in male Barilius bendelisis (Ham.).

The study reveals that pre-ovulatory females of the fish Barilius bendelisis (Ham.) release sex steroids and their conjugates into the water and that a steroid sulphate of these compounds functions as a potent sex pheromone which stimulates milt production in conspecific males prior to spawning. Since males exposed to the purified subfraction III of the steroid sulphate fraction have increased milt volume and more spermatozoa with greater motility, the function of this priming pheromone appears to be to enhance male spawning success. High turbulence and faster water currents render the hillstream ecosystem extremely challenging for chemical communication. Therefore, ovulatory female fish secrete highly water soluble steroid sulphates for rapid pheromonal action in males. Inhibited milt volume in olfactory tract lesioned (OTL) males exposed to the steroid sulphate fraction and 17alpha,20 beta-dihydroxy-4-pregnen-3-one supports the concept that the pheromonally induced priming effect in male fish is mediated through olfactory pathways.

Neurodepressive action of a piscicidal glycoside of plant, Aesculus indica (Colebr.) in fish.

Sublethal concentration (2.6 mg/l) of a triterpene based piscicidal glycoside of A. indica damaged the neurons, fibre tracts and central correlation sites for gustatory, tactile and visceral sensory impulses in medulla oblongata of fish after prolonged poisoning. The fear, sinking to bottom, lack of schooling and non discriminatory pattern in treated fish were because of neurodepression. The jerky movement, ventilatory inefficiency, swallowing air bubbles and light pinkness of gills were due to the degradation of respiratory centres in the vagal lobes of toxified fish.

Neurolytic manifestation of piscicidal flavanoid of plant, Engelhardtia colebrookiana (Lindle) in fish.

The sublethal concentration 6 mg.l-1 of a piscicidal flavanoid, 'Quercetin glycoside', obtained from E. colebrookiana affected neuro-architecture in medulla oblongata of freshwater fish, Barilius bendelisis (Ham.), at 32 days exposure. Since medulla of fish is primary centre for the reception of several incoming stimuli, the breakdown of neurons and their neuraxes in facial and vagal lobes impaired the transmission of sensory informations to cerebellum. Consequently fish became unconscious and could be caught easily with hands. The symptoms like lack of schooling, lack of response to food and external stimuli, sluggishness, incapability of maintaining body posture and uncoordinated functioning are accounted for by the neurolysis in hind brain of fish.