Sudden Changes in Water Hardness Do Not Impact Short-Term Rainbow Trout Survival

Fish transferred from hard water to soft water, as can occur during the stocking of hatchery-reared fish into natural environments, experience many physiological stressors that can cause mortality. This study consisted of four trials examining the effects of direct transfer from hard (345 mg/L CaCO3) to soft water on mortality and glucose stress response of two different sizes and strains of rainbow trout Oncorhynchus mykiss. The first trial subjected 90 g Shasta strain rainbow trout to a direct transfer to soft water (70 or 160 mg/L as CaCO3). The second trial used the same strain and size trout, with transfer to lower hardness values of either 0 or 35 mg/L. The third and fourth trials used 3 to 5 g Arlee strain rainbow trout. The third trial transferred the fish from 345 mg/L hardness water to water at a hardness of either 0 or 35 mg/L. The fourth trial added a secondary temperature stressor of 20 °C (versus the experimental standard of 11 °C) in combination with a hardness level of 0 mg/L. In every trial, survival was not significantly different among all treatments. Sudden and extreme changes in water hardness, even in combination with increased water temperature, did not cause trout mortality. There was also no significant difference in blood glucose over time among any of the treatments in the first three trials. In the fourth trial, glucose values did significantly vary among the treatments at 48 and 168 h after the start of the trial. However, all glucose values were relatively close to the basal level. These results indicate that changes in water hardness likely do not impact the survival of rainbow trout, negating the need for tempering or acclimation

Bioprocessed soybean meal replacement of fish meal in rainbow trout (Oncorhynchus mykiss) diets

This 125-day experiment evaluated the growth of adult rainbow trout (Oncorhynchus mykiss) fed one of three isonitrogenous and isocaloric diets (46% protein, 16% lipid). Fish meal was the primary protein source for the reference diet, which was compared to two other diets where bioprocessed soybean meal replaced 60% or 80% of the dietary fish meal. At the end of the experiment, there were no significant differences in gain, percent gain, feed conversion ratio, or specific growth rate among the dietary treatments. There were also no significant differences in intestinal morphology, splenosomatic index, hepatosomatic index, and viscerosomatic index among the diets. Based on these results, bioprocessed soybean meal can replace at least 80% of the fish meal in adult rainbow trout diets

Behavioral Response of Multiple Rainbow Trout to Vertically Suspended Environmental Enrichment

Vertically suspended environmental enrichment improves the rearing performance of fish during aquaculture production, but the reason for this improvement is unclear. This study documented the behavior of groups of rainbow trout (Oncorhynchus mykiss), as indicated by their in-tank location preferences, in response to vertically suspended structure. The location of both experienced and naïve fish (with or without prior exposure to vertically suspended enrichment) in both barren and enriched tanks was recorded. In-tank locations were significantly different for experienced fish in both barren and enriched tanks but were similar for naïve fish. When observations were combined for both the presence and absence of enrichment, naïve fish locations were significantly different from experienced fish. Locations were also significantly different for all fish in enriched compared to barren tanks. These results indicate that trout location is influenced by the presence of vertically suspended environmental enrichment and that learning from prior experience with enrichment occurs

17β-Estradiol Can Induce Sex Reversal in Brown Trout

Hormones have been used to change phenotypic sex in many fish species. However, information specific to changing sex in brown trout Salmo trutta is lacking. This study compared the effectiveness of two different 17β-estradiol (estradiol) concentrations (20 mg/kg and 30 mg/kg) fed to brown trout for 60 days, beginning at initial feeding. At 456 days post-initial feeding, the 20 mg/kg and 30 mg/kg treatment groups were 84% and 86% female, respectively. These values were significantly higher than the 47% females observed in the control group which did not receive dietary estradiol. At the end of the 60-day estradiol treatment period, weight gain, percent weight gain, and feed conversion ratio were all significantly lower in the tanks of fish receiving estradiol than in the control tanks. Individual fish fed estradiol also weighed significantly less and were significantly shorter than the fish not receiving estradiol-coated feed. Mortality ranged from 1.0 to 2.4% among the treatments and was not significantly different. After 105 days post-initial feeding, weight gain, percent weight gain, and feed conversion ratio were not significantly different among the treatments. At 456 days post-initial feeding, individual fish were significantly longer and heavier in the 20 mg/kg estradiol treatment compared to the fish in the control treatment, and the fish in the 30 mg/kg estradiol treatment were similar to the other two treatments. This study is the first to document the successful sex reversal of brown trout using estradiol. While the estradiol treatments used in this study did not lead to complete feminization, the observed 85-to-15% female-to-male phenotypic ratio indicates the successful feminization of genetic males. The levels of feminization observed in this study are suitable for this initial step to potentially develop a YY male broodstock to control invasive brown trout populations

17β-Estradiol Can Induce Sex Reversal in Brown Trout

Hormones have been used to change phenotypic sex in many fish species. However, information specific to changing sex in brown trout Salmo trutta is lacking. This study compared the effectiveness of two different 17β-estradiol (estradiol) concentrations (20 mg/kg and 30 mg/kg) fed to brown trout for 60 days, beginning at initial feeding. At 456 days post-initial feeding, the 20 mg/kg and 30 mg/kg treatment groups were 84% and 86% female, respectively. These values were significantly higher than the 47% females observed in the control group which did not receive dietary estradiol. At the end of the 60-day estradiol treatment period, weight gain, percent weight gain, and feed conversion ratio were all significantly lower in the tanks of fish receiving estradiol than in the control tanks. Individual fish fed estradiol also weighed significantly less and were significantly shorter than the fish not receiving estradiol-coated feed. Mortality ranged from 1.0 to 2.4% among the treatments and was not significantly different. After 105 days post-initial feeding, weight gain, percent weight gain, and feed conversion ratio were not significantly different among the treatments. At 456 days post-initial feeding, individual fish were significantly longer and heavier in the 20 mg/kg estradiol treatment compared to the fish in the control treatment, and the fish in the 30 mg/kg estradiol treatment were similar to the other two treatments. This study is the first to document the successful sex reversal of brown trout using estradiol. While the estradiol treatments used in this study did not lead to complete feminization, the observed 85-to-15% female-to-male phenotypic ratio indicates the successful feminization of genetic males. The levels of feminization observed in this study are suitable for this initial step to potentially develop a YY male broodstock to control invasive brown trout populations

Master plans for pedestrian and bicycle transportation: community characteristics

Background:Recent research demonstrates the importance of targeting the built environment to support individual physical activity, particularly for people experiencing health disparities. Master plans to promote biking and/or pedestrians (BPMPs) are a potential method for environmental change. This descriptive study aims to provide a snapshot of plan attributes and better understand demographic, social and transportation characteristics of communities with BPMPs. Methods: We collected a census sample of BPMPs from 4 states. Population and commuting data were obtained from national statistics. Results: 294 master plans were included, with most plans representing municipalities. 62% of plans targeted biking only, one-fifth targeted biking and walking, and 15% targeted walking only. The sampled locations have a similar demographic profile as the overall U.S. for median age and household income, people of color, high school education, and income inequality. The degree of racial diversity of sampled communities is slightly less than the U.S. average and the percentage of people who walk to work were slightly higher. Conclusions: Given that communities with master plans have a similar profile as the overall U.S., BPMPs could feasibly be spread to communities throughout the country. Further research is planned to describe BPMPs in detail toward informing future plan development