Abstract-4-Nonylphenol (NP) is a degradation product of nonylphenol polyethoxylates, a major group of nonionic surfactants. When Japanese medaka, Oryzias latipes were exposed from hatch to 3 months of age to aqueous solutions of NP at nominal concentrations of 10, 50, and 100 g/L, 50% of the male fish in the 50-g/L treatment and 86% of the males in the 100-g/L treatment developed testis-ova, an intersex condition characterized by both testicular and ovarian tissue in the gonad. The ratios of males to females in the control treatment (2:1, M:F) and the 100-g/L NP treatment (1:2, M:F) were also significantly different. The LOAEC for induction of testis-ova at a nominal concentration of 50 g/L NP is slightly greater than the upper range of concentrations of NP that have been reported in final effluents from municipal sewage treatment plants. Studies on the environmental fate of nonylphenol ethoxylates and degradation products in the aquatic environment are needed to assess the significance of these data in terms of potential reproductive effects in feral fish populations.

Information about animal movements has often been inferred from stable isotope analysis (SIA), but is dependent on animals assimilating site-specific isotopic signatures via diet. This potential weakness in ecological interpretation can be overcome by using other investigative tools that provide precise information about individual movement patterns. In this paper, we demonstrate the value of combining SIA with telemetry or mark-recapture data from trapping, electrofishing and remote detection of individuals to study the movement and feeding ecology of fishes in different habitats. In a fjord lake system in Newfoundland, Canada, juvenile Atlantic salmon delayed downstream migration (smolts) or actively moved into a large lake (parr) where they foraged for periods reflecting different life history strategies. In the Miramichi River (New Brunswick, Canada), SIA provided evidence of distinct foraging habitats (tributary versus large river). By tracking fish implanted with passive integrated transponder (PIT) tags, we distinguished between movements related to foraging versus seeking cool water refugia during high temperature events. Finally, site fidelity and limited mobility of slimy sculpin, a small benthic fish, was established where delta13C in muscle tissue showed a progressive enrichment downstream and where a median displacement of <10 m was estimated for sculpin tagged with PIT tags. Technological improvements have permitted non-destructive tissue sampling of wild fishes for SIA, and the tagging and remote detection of animals smaller than was previously possible. These advancements and the combination of investigative tools promise new insights into animal ecology.

Previous measurements of stable isotope ratios in fishes have typically used white muscle, but potential applications exist for the use of other tissues. We tested three tissues (liver, fin, and gonad) in three freshwater species (juvenile Atlantic salmon Salmo salar, slimy sculpin Cottus cognatus, and brook trout Salvelinus fontinalis) to investigate potential ecological applications of stable isotopes in tissues other than muscle. Caudal fin tissue correlated closely with muscle tissue for Atlantic salmon and brook trout for ␦ 13 C (r ϭ 0.96 and 0.94, respectively) and ␦ 15 N (r ϭ 0.80 and 0.74). Liver ␦ 13 C values were tightly linked to muscle values, and differences were due to lipid effects. Associations between liver and muscle ␦ 15 N suggested subtle changes in nutritional status. Isotope ratios of gonads differed markedly between male and female slimy sculpin; these differences were probably governed by differences in the allocation of specific nutrients. Knowledge of isotopic fractionation among tissues will aid fish biologists in nonlethal sampling of fishes for stable isotope analysis and in using stable isotopes to assess nutritional status and the allocation of nutrients to reproduction.

Abstract-There are many endocrine-disrupting chemicals in the environment that have the potential to alter the development of sexual characteristics in fish and wildlife. Little is known about the factors that influence the development of an intersex condition in fish. Japanese medaka (Oryzias latipes) were exposed to octylphenol (OP), a known estrogen agonist, during various life history stages to determine the factors that control induction of testis-ova, an intersex condition. In male medaka exposed to OP (100 g/L) beginning at 1, 3, 7, 21, and 35 d posthatch, the incidence of testis-ova at 100 d posthatch was highest in the 3-d posthatch treatment (4 of 14 males) and declined when exposures were initiated with older fry. Exposure to OP (100 g/L) from hatch for a period of 1 or 2 months did not induce testis-ova, but exposure for 3 months resulted in 3 of 50 males developing this condition. Exposures of adult male medaka to OP (200 and 300 g/L) for either 18 or 36 d resulted in only one testis-ova in a male fish exposed for 36 d to the highest nominal concentration. In addition to testis-ova, male medaka exposed to OP developed testicular fibrosis. Overall, these data indicate that prolonged exposure of male medaka to an estrogen agonist beginning around the period of gonadal differentiation is optimal for the development of testis-ova, but this intersex condition can be induced when exposure begins at later life stages.

Concerns regarding sentinel species for assessing environmental impacts include residency, abundance, and suitability for measuring responses, if effects are to be attributable to local conditions. Stable isotope analysis was used as a tool to investigate site fidelity of slimy sculpin (Cottus cognatus) to establish residency and exposure for the sculpin. We predicted that sculpin collected from sites adjacent to agricultural activity would show higher δ15N values than those collected from sites in forested areas because of isotopic enrichment by fertilizers in the former. The predominant use of chemical fertilizer applications in the region, however, resulted in no specific enrichment of 15N in sculpin collected in the agricultural region. However, there was an incremental enrichment in the fish muscle tissue of approximately 5‰ in δ13C values in a downstream direction, irrespective of surrounding land use. As a result, the dual-isotope comparison was successful at demonstrating site-specific isotopic signatures across sites for 30 km of the river system. The site-specific signatures suggest that slimy sculpin are not moving considerable distances among sites and are incorporating their isotopic signatures over a narrow spatial scale. The results support the use of the slimy sculpin as a sentinel species for investigating site-specific environmental impacts.