Responses of round goby (Neogobius melanostomus) olfactory epithelium to steroids released by reproductive males

The wild perciform teleost Neogobius melanostomus (the round goby) originated from the Ponto-Caspian region and is now a highly successful invasive species in the Laurentian Great Lakes. Males may attract females into their nests for spawning by releasing reproductive pheromones, and it has been previously shown that reproductive males synthesize and release the 5β-reduced and 3α-hydroxyl steroids 3α-hydroxy-5β-androstane-11,17-dione (11-oxo-etiocholanolone; 11-O-ETIO) and 3α-hydroxy-5β-androstane-11,17-dione 3-sulfate (11-oxo-etiocholanolone-3-sulfate; 11-O-ETIO-3-s) and 3α,17β-dihydroxy-5β-androstan-11-one 17-sulfate. In this study, we investigated properties of these released steroids by recording field potential responses from the olfactory epithelium (electro-olfactogram, EOG). The steroid 3α,17β-dihydroxy-5β-androstan-11-one 17-sulfate did not elicit olfactory responses while both 11-O-ETIO and 11-O-ETIO-3-s stimulated olfactory field potentials in the round goby, but not in the goldfish. Cross-adaptation analysis demonstrated that round gobies discriminated between11-O-ETIO and 11-O-ETIO-3-s (as well as etiocholanolone, ETIO) at the sensory level. Second messenger cascades depending on both cAMP and IP3 were inferred for steroids from pharmacological inhibition studies, while the canonical teleost odors taurocholic acid (a bile acid) and l-alanine (an amino acid) used only cAMP and IP3, respectively. The round goby presents itself as an excellent species for the study of olfactory function of fish in the wild, given its possible use of these released steroids as pheromones

The Effect of Elevated Steroids Released by Reproductive Male Round Gobies, Neogobius melanostomus, on Olfactory Responses in Females

The round goby, Neogobius melanostomus, is a highly successful invasive species in the Laurentian Great Lakes. Previous behavioral studies implied that females are attracted by pheromones to the nests of reproductive males, and that males release putative steroidal pheromones—unconjugated as well as conjugated forms of 3α-hydroxy-5β-androstane-11,17-dione (11-O-ETIO)—following stimulation of the hypothalamic-gonadal axis with salmon gonadotropin releasing hormone analog (sGnRHa). In this study, we tested the olfactory system of females in response to extracts containing these released steroids. We compared electrical field potential responses from the olfactory epithelium (electro-olfactogram, EOG) of non-reproductive females to methanol extracts of water that previously held males, collected before and after injection of the males with sGnRHa or saline. The females showed increased EOG responses to the post-injection extracts when males were treated with sGnRHa but not saline. This finding provides further evidence for interactions between male and female N. melanostomus via steroidal reproductive pheromones

Response to putative round goby (Neogobius melanostomus) pheromones by centrarchid and percid fish species in the Laurentian Great Lakes

Pheromone trapping is an increasingly viable strategy to reduce invasive fish populations, largely due to the pheromones\u27 function of evoking behavioral responses among conspecifics. Prior to attempting such population control techniques, the pheromones must be identified and their possible influences on non-target species addressed. The round goby (Neogobius melanostomus) is a species invasive to the Great Lakes region, and negatively impacts the ecosystem by interfering with local fish populations. At least two 5β-reduced 3α-hydroxyl steroids released by reproductive N. melanostomus (11-O-ETIO and 11-O-ETIO-3s) evoke olfactory sensory responses from the olfactory epithelium of conspecifics, and water conditioned by reproductive males (containing these steroids) attracts female round gobies. In this study, we examined whether these putative pheromones, along with simultaneously-released 11-O-ETIO-17s, stimulate olfactory sensory responses from alternative fish species sharing the same ecosystem as N. melanostomus in the Great Lakes region. Rock bass (Ambloplites rupestris), bluegill sunfish (Lepomis macrochirus), pumpkinseed sunfish (Lepomis gibbosus), smallmouth bass (Micropterus dolomieu), and yellow perch (Perca flavescens) were the targets of an electro-olfactogram experiment designed to record responses to odors. When compared to round goby responses from previous studies, amino acids and the bile acid consistently elicited electro-olfactogram responses across all species, but only round gobies showed a response to the putative pheromones. This study supports the concept of conducting a pheromone trapping trial in the field without adversely affecting the olfactory responses of non-target fish in the area