The effects of temperature on the physiological response to low oxygen in Atlantic sturgeon

Atlantic sturgeon (Acipenser oxyrhynchus), which are bottom dwelling and migratory fish, experience environmental hypoxia in their natural environment. Atlantic sturgeon, acclimated to either 5 or 15°C, were subjected to a 1 h severe (<10 mm Hg) hypoxia challenge in order to document their physiological responses. We measured hematological parameters, including O₂ transport (hemoglobin, hematocrit), ionic (chloride, osmolality), and metabolic (glucose, lactate) variables under normoxic conditions (~160 mm Hg), immediately following a 1 h exposure to hypoxic water, and following a further 2 h of recovery from this challenge in normoxic water. In a second experiment, we assessed the opercular beat frequency before, during, and after hypoxic exposure. Hemoglobin concentrations and hematocrit were significantly different between fish held at 5°C vs. 15°C and also significantly different between normoxia prior to hypoxia and following recovery. Plasma lactate concentrations increased following hypoxia at both temperatures, indicative of an increase in anaerobic metabolism. In contrast, a significant increase in plasma glucose concentrations in response to hypoxia only occurred at 5°C, suggesting different fuel demands under different temperatures. Changes in opercular beat frequency (OBF) were dependent on temperature. At 5°C, OBF increased upon exposure to hypoxia, but returned to pre-exposure levels within 35 min for the remainder of the experiment. During hypoxia at 15°C, OBF increased very briefly, but then rapidly (within 20 min) decreased to levels below control values. Following a return to normoxia, OBF quickly increased to control levels. Overall, these findings suggest that Atlantic sturgeons are relatively tolerant to short-term and severe hypoxic stress, and the strategies for hypoxia tolerance may be temperature dependent.     

Fishing for conservation of freshwater tropical fishes in the Anthropocene

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Livestock and livelihoods of smallholder cattle-owning households in Cambodia: the contribution of on-farm and off-farm activities to income and food security

The majority of smallholder farming households in Cambodia are rurally based and rely on agriculture to support their livelihoods. However, in recent years, growth in the agriculture sector has stagnated with farmers facing several challenges including declining prices for traditional crops and irregular rainfall patterns. This has led to a need for farmers to diversify income sources with livestock promoted as a more viable livelihood activity, particularly the raising of cattle and poultry. However, uncertain profitability of livestock activities is a common perception by smallholders, especially where animals have not been traditionally viewed as a primary income source. To address this, information is required which compares the income and expenses associated with livestock raising to other on-farm activities and off-farm sources. This study reports on a survey of livelihood survey of 17 male and 21 female representatives of 20 households owning cattle in Cambodia, comparing the associated income and expenses of the various livelihood activities in the 12-month period from January to December 2016. Combined total household income from both on-farm and off-farm sources ranged from USD875 to 17730 with an average of USD6779, representing 51% and 49% from on-farm and off-farm activities, respectively. Cattle raising was the most common source of on-farm income (85%), contributing USD1064 and representing 22% of total household income. General household expenses, such as food and transportation (including expenses associated with off-farm employment), represented the majority of total household expenses (79%). Gross profit calculations indicated higher values for pig raising (USD1841.79), cattle (USD950.80) and non-rice crops (USD884) whilst the highest gross margin value was recorded for cattle (89.33%) followed by vegetables (85.27%) and non-rice crops (83.08%). Whilst wet season and dry season rice returned a negative gross profit value of USD197.27 and USD90.60 on average per household, respectively, both were ranked as most important for household consumption, followed by poultry, providing the main source of energy (rice) and protein (chicken meat) and sustaining household food requirements. The study concludes that although smallholder cattle-owning households in Cambodia undertake a diverse range of on-farm activities, as cattle raising provides a superior income source due to higher returns and lower variable costs, it could be promoted as a preferred livelihood activity by agencies conducting rural extension activities. Although consideration of available labour and monetary funds to invest in cattle raising is required, it was observed that income from off-farm sources may prove beneficial in providing the additional monetary funds to support cattle-raising activities and assist in providing generally poor smallholder households with enhanced economic resilience.     

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