Temperature-dependent weight gain of Gulf coast and northern strain walleye Sander vitreus fingerlings was determined by rearing fish in flow-through aquaria at different water temperatures (range 15-32°C). Maximum growth of Gulf coast and northern strain walleye occurred between 20 and 26°C, and weight gain of northern walleye exceeded that of the Gulf coast strain by 1.5 times. An acclimated chronic exposure method to assess upper thermal limits determined that walleye survived 35, 9, and 1 days at 33, 34, and 35°C, respectively. A post pond-rearing feed-training practice (21 d) at a mean density of 6,290 ± 1,247 fish/m3 using formulated feeds was successful (32-85% survival), and walleye continued to consume a formulated diet feed after stocked at densities of 12,250 and 24,700/ha into 0.04 ha earthen ponds. After 125 days, survival in ponds was poor (< 30%) and production varied substantially.

Average global ocean temperatures and the frequency and intensity of marine heat waves have been increasing over the last century. Temperature plays a critical role in defining the geographical range of the majority of marine species. Some species may respond to ocean warming trends by shifting their latitudinal and depth ranges, while others may be able to cope with changes in temperature through phenotypic plasticity and local adaptations. If a species is unable to shift its distribution or has limited thermal plasticity, it may face severe population declines or local extinction. Therefore, describing thermal tolerance limits is a useful tool for predicting how a given species will respond to ocean warming. Due to its commercial importance, sablefish (Anoplopoma fimbria) is a fish species of particular interest in British Columbia. Sablefish are semi-demersal and spawn along the continental slopes of the Pacific coast from California to Alaska. Their various life history stages occupy different depth strata and thus experience substantially different environments with respect to temperature (as well as salinity, oxygen, etc.). Adult sablefish spawn at depths that exceed 300 m and embryos sink to depths of ~1,000 m after fertilization. Embryos hatch into yolk-sac larvae until they become mobile at the post-yolk-sac larvae stage. The latter migrate to near-surface waters (<3 m) at which temperatures are approximately 12-15°C in the late spring. Heart rate is a temperature-dependent performance measure and has been used to gain insight into the thermal tolerance of many adult fishes. However, few studies have used this approach with the early life stages of fishes such as embryos and yolk-sac larvae (YSL). The purpose of this study was to assess whether sablefish embryos and YSL have the potential for cardiac acclimation by examining changes in their thermal tolerance limits when incubated at temperatures outside of what they experience in a natural setting (~5°C). Cardiac performance was assessed during an acute temperature challenge from 2.0° to 12.0°C in increments of 1.0°C (at a rate of 1°C 40 min-1) for individuals incubated at 3.0°C, 5.0°C (control), and 7.0°C. Embryos were video recorded at each 1.0°C increment and videos were viewed at a later date to determine heart rate at each temperature. This study attempted to use temperature breakpoint analysis, commonly used in studies of adults, on these early life stages to assess cardiac performance. It was hypothesized that sablefish embryos and yolk-sac larvae incubated at warmer temperatures would have a higher thermal tolerance than sablefish embryos and YSL incubated at colder temperatures, as seen in other fish species. There was some degree of thermal compensation of cardiac function with temperature in sablefish embryos and YSL as mean heart rate increased with incubation temperature throughout acute warming. YSL had consistently higher mean heart rate values at any given temperature of the acute temperature challenge when compared to embryos incubated at the same temperature. TAR is the temperature at which the heart first becomes arrhythmic is considered a sub-lethal index because the organism is expected to experience cardiac collapse soon after. TAR was reached for 100% of embryos incubated at 3.0°C at an average temperature of 8.6 ± 1.0°C. In contrast, only 18% and 33% of embryos incubated at 5.0° and 7.0°C exhibited arrhythmia (mean TAR were 9.0 ± 3.0 and 8.5± 1.5°C, respectively). The lower thermal limit for embryos incubated at 7.0°C was likely near 1.0°C, which was determined during preliminary testing. Neither the upper or lower limits were reached for YSL during the acute temperature challenge. No mortalities were observed during any acute temperature challenges. Overall percent mortality throughout the entirety of the experiment could not be determined due to limitations in the experimental setup and reduced staff working on this project due to COVID-19 safety protocols. This study is also the first to investigate whether transporting sablefish embryos from a hatchery to a research facility at different stages of development had an effect on their cardiac performance during acute warming. Embryos were transported in a cooler from the sablefish hatchery on Salt Spring Island to UVic via ferry and vehicular transport. Time of transportation did not significantly change the temperature at which heart rate reaches its maximum or TAR. There was also consistent overlap in mean heart rate ± standard error at each temperature of the acute temperature challenge between these two groups. Therefore, there appears to be no indication that transportation affected the heart rate response of sablefish embryos when incubated at the same temperature. However, future studies may want to confirm this by identifying and comparing other breakpoint temperatures that characterize physiological performance. Determining whether transportation has effects on cardiac performance may be of interest to other researchers who need to transport fish embryos from the field to the laboratory. Heart rate measurements during an acute temperature challenge of sablefish embryos and yolk-sac larvae (YSL) incubated at various temperatures provided initial insight to their overall success in a warming climate. Currently, it is projected that waters at depths of 1,000 m will warm on average by less than a degree by the end of the 21st century. The results of this study suggest that the early life stages of sablefish may not be exposed to critical temperatures in the near future, but future impacts on overall physiological decline remain unknown. The novel data presented here lay the groundwork for future researchers to continue to characterize the thermal tolerances of the early life stages of sablefish, and the likely response of this important species to ocean warming. / Graduate

Opportunistic premise plumbing pathogens (OPPPs) are responsible for many infections linked to drinking water. The annual cost of disease caused by these waterborne pathogens is $850 million. Key characteristics of these opportunistic waterborne pathogens include: disinfectant- resistant, biofilm formation, thermal-tolerance, desiccation-resistant, growth in amoebae and growth in low oxygen conditions. Methylobacterium spp. have been recognized as an emerging OPPP, so the purpose of this study was to investigate these waterborne bacteria in more detail to determine whether they have all characteristics of OPPPs. Seven Methylobacterium spp. strains were studied to measure growth in laboratory broth medium and drinking water, measure hydrophobicity on surfaces found in household plumbing, measure adherence and biofilm formation to surfaces found in household plumbing and measure susceptibility to hot water heater temperatures. Methylobacterium spp. were found to aggregate in lab broth medium and drinking water, hydrophobic on different surfaces in household plumbing, adhere readily and form biofilm on different surfaces and thermal-tolerant to water heater temperatures. These results support and identify Methylobacterium spp. as opportunistic premise plumbing pathogens. / Master of Science

Temperature is a fundamental environmental force shaping species abundance and distributions through its effects on biochemical reaction rates, metabolism, activity, and reproduction. In light of future climate shifts, mainly driven by temperature increases, how will organisms persist in warmer environments? One molecular mechanism that may play an important role in coping with heat stress is the heat shock response (HSR), which protects against molecular damage. To prevent and repair protein damage specifically, Hsps activate and become up-regulated. However, the functional diversity and relevance of heat shock proteins (Hsps) in extending upper thermal limits in taxonomic groups outside marine and model systems is poorly understood. Ants are a good system to understand the physiological mechanisms for coping with heat stress because they have successfully diversified into thermally stressful environments. To identify and characterize the functional diversity of Hsps in ants, I surveyed Hsp orthologues from published ant genomes to test for signatures of positive selection and to reconstruct their evolutionary history. Within Hymenoptera, ants utilize unique sets of Hsps for the HSR. Stabilizing selection was the prevailing force among Hsp orthologues, suggesting that protein activity is conserved. At the same time, regulatory regions (promoters) governing transcriptional up-regulation diversified: species differ in the number and location of heat shock elements (HSEs). Therefore, Hsp expression patterns may be a target for selection in warm environments. I tested whether Hsp expression corresponded with variation in upper thermal limits in forest ant species within the genus Aphaenogaster. Whole colonies were collected throughout the eastern United States and were lab acclimated. There was a positive relationship between upper thermal limits (Critical Thermal maxima, CTmax) and local temperature extremes. Upper thermal limits were also higher in ant species that lived in open habitats (shrub-oak and long-leaf pine savannah) than species occupying closed habitats (deciduous forest). Ant species with higher CTmax expressed Hsps more slowly, at higher temperatures, and at higher maximum levels than those with low CTmax. Because Hsps sense and repair molecular damage, these results suggest the proteomes of open relative to closed canopy forests are more stable. Although deciduous forest ant species may be buffered from temperature stress, it is likely that temperature interacts with other environmental stressors such as water and nutrient availability that may impact upper thermal limits. I measured the influence of dehydration and nutrition stress on upper thermal limits of forest ants from a single population. Ants that were initially starved were much less thermally tolerant than controls and ants that were initially desiccated. Because ants are likely to experience similar combination of stressors in the wild, upper thermal limits may be severely overestimated in single factor experiments. Therefore, realistic forecasting models need to consider multiple environmental stressors. Overall, adaptive tuning of Hsp expression that reflects better protection and tolerance of protein unfolding may have facilitated ant diversification into warm environments. However, additional stressors and mechanisms may constrain the evolution of upper thermal limits.

As mudanças climáticas influenciarão as médias de temperaturas ambientais e a frequência de eventos extremos com consequências ainda desconhecidas para a fauna. Conhecer os limites fisiológicos dos organismos ao aumento de temperatura pode ajudar a ampliar os marcos conceituais dos impactos regionais das mudanças climáticas sobre a fauna. Este trabalho abordou como a diversidade fisiológica representada pela tolerância termal da fauna de artrópodes terrestres estava relacionada entre os biomas do Brasil, em uma perspectiva macrofisiológica (ampla escala espacial). Especificamente, coletou-se a temperatura crítica máxima (TCMax) de espécimens de artrópodes das Classes Arachnida, Chilopoda, Dipoploda, Entognatha (Collembola), Insecta e Malacostraca (Oniscidea) nos biomas de Mata Atlântica (strictu sensu), Mata Atlântica de Altitude, Cerrado, Amazônia e Caatinga. Os artrópodes foram utilizados como modelo de estudo por permitirem uma associação mais clara com a teoria disponível sobre limites fisiológicos e o ambiente físico. Assim, foram investigados padrões de variação da TCMax entre e dentro dos biomas, considerando ou não a categoria sistemática. Igualmente, foi avaliada a relação da TCMax da fauna de artrópodes com variáveis bioclimáticas representantes do ambiente termal nos biomas. No aspecto de margem de segurança termal, avaliou-se a potencial tolerância ao aquecimento da fauna de artrópodes nos biomas. Os resultados mostraram que existe ampla diversidade fisiológica da fauna de artrópodes, com padrões atrelados aos biomas do Brasil. A relação do padrão de tolerância termal dos espécimens de artrópodes com o bioma é complexa, havendo nuances de variação dentro e entre os biomas. Houve grande proporção de fauna termotolerante no bioma da Caatinga e menor proporção de fauna termotolerante na Mata Atlântica. Quanto às margens de segurança termal, os dados de tolerância ao aquecimento sugerem que não há grande susceptibilidade ao aquecimento da fauna de artrópodes nos biomas do Brasil. Este trabalho contribui para ampliar a discussão dos possíveis impactos das mudanças climáticas em seus aspectos regionais, tendo em vista a diversidade fisiológica da fauna de artrópodes terrestres nos biomas brasileiros. Igualmente, os dados podem servir como uma importante base para a incorporação em avaliações globais da vulnerabilidade dos ectotérmicos frente às mudanças do clima / Climate change will affect the average environmental temperatures and the frequency of extreme events with still unknown consequences for wildlife. To understand the physiological limits of organisms in relation to the increase in environmental temperature can help extend the conceptual frameworks of climate change regional impacts on wildlife. This work discussed how the physiological diversity represented by the thermal tolerance of terrestrial arthropod fauna was related among biomes of Brazil in a macrophysiological perspective (large spatial scale). It was collected critical thermal maximum (CTMax) of specimens of the class Arachnida, Chilopoda, Dipoploda, Entognatha (Collembola), Insecta and Malacostraca (Oniscidea) in the biomes of the Atlantic Forest (strictu sensu), Atlantic Forest Highland, Cerrado (Brazilian Savanna), Amazonia and Caatinga. The arthropods were used as model to allow a better association with the available theory of physiological limits and the physical environment. Thus, it was investigated variation in patterns of CTMax between and within biomes considering or not the systematic category. It was also evaluated the relationship of CTMax of the arthropod fauna with bioclimatic variables as representative of the thermal environment in the biomes. In terms of thermal safety margin, it was evaluated potential warming tolerance of the arthropod fauna in the biomes. The results showed that there is a broad physiological diversity of arthropod fauna with patterns linked to brazilian biomes. The ratio between thermal tolerance patterns of arthropod specimens and the biome is complex, there were varying nuances within and between biomes. There is a large proportion of thermotolerant fauna in the Caatinga biome and a lesser proportion of thermotolerant fauna in the Atlantic Forest. The warming tolerance data suggest that the susceptibility to heat of the arthropod fauna in brazilian biomes is small. This work will help to expand discussions of potential impacts of climate change regional aspects considering the view of the physiological diversity of terrestrial arthropod fauna in the brazilian biomes. In addition, the data can be as an important basis for incorporation into global vulnerability assessments on terrestrial ectotherms in view of climate change

The aquatic zooplankton crustacean Daphnia magna must be able to tolerate thermal stress in order to survive their native shallow ponds that are susceptible to drastic seasonal and diurnal temperature fluctuations as well as to globally increasing temperatures. Survival in such variable environments requires plastic responses that must include fundamental aspects of Daphnia biochemistry and physiology. Adaptive response to selection favoring such plastic phenotypes requires the presence of genetic variation for plastic response in natural populations. Adverse effects of elevated temperature on aquatic organisms are diverse and so are their plastic responses; among the most severe challenges aquatic organisms face when exposed to heat is the elevated oxidative stress. In this work we focused on short-term and long-term responses of Daphnia to temperature changes that increase its resistance to oxidative stress. Daphnia acclimated to stressful but non-lethal temperature (28ºC) show longer survive during exposure to a lethal temperature (37ºC) than those acclimated to the optimal temperature (18ºC). Short-term reciprocal switches between 18ºC and 28ºC result in intermediate temperature tolerance. These changes are accompanied by mirroring changes in total antioxidant capacity indicating the increased antioxidant capacity as a possible causative mechanism for heat tolerance gained from acclimation. The analysis of 6 geographically distinct genotypes representing a range of temperature tolerance levels shows a genetic difference in response to short-term and long-term acclimation as well as in the effect of antioxidant capacity on temperature tolerance. These results indicate a significant degree of local adaptation in heat and oxidative stress defenses in Daphnia and provide a better understanding of adaptive responses of this zooplankton crustacean to rising temperatures.

Anthropogenic climate warming is predicted to accelerate over the next century, with potentially dramatic consequences for wildlife. It is important to understand as well as possible how different organisms will respond to this stress. This project seeks to gain a better mechanistic understanding of the thermal biology of the Glanville Fritillary butterfly (Melitaea cinxia) at the latitudinal and elevational extremes of its range. Investigation of the temperatures at which adult butterflies took spontaneous flight revealed a significant difference between populations from the elevational extremes, with insects from high elevation taking flight at lower thoracic temperatures than those from low elevation. Contrary to expectation, there was no systematic effect of latitude on takeoff temperature. If these measures represent adaptation to climate, then these effects are not simple and the influences of elevation and latitude are not the same. Investigation of thermal tolerance across all life cycle stages found no difference in larval performance between the populations tested. There was however an effect of treatment. This suggests that in M. cinxia, even populations from different extremes of the range may not differ in their thermal tolerance. The effect of treatment suggests that there is temperature-induced plasticity. The adaptive significance of this has been explored to some extent. Investigation of heat shock protein expression between the latitudinal extremes finds no difference in Hsp21.4 expression when exposed to heat stress, however both Hsp20.4 and Hsp90 were upregulated in response to heat stress. For Hsp20.4, there were significant differences in expression between the populations. Finally, a species distribution model using maximum entropy techniques was conducted for M. cinxia, predicting both the current and future (2100) distributions of the species. The model closely matches the known current distribution, and predicts a clear northward range shift in response to climate change. / text

Made available in DSpace on 2016-08-15T20:31:16Z (GMT). No. of bitstreams: 1 NoeideSF_DISSERT.pdf: 1291581 bytes, checksum: 5459c2431224e1b75c0881d65fd5dfc8 (MD5) Previous issue date: 2014-02-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In stingless bees (Hymenoptera, Apidae, Meliponini), so far, thermal tolerance and social thermoregulation have received little scientific interest. Yet, both these topics are fundamental to understand the evolution of sociality and of the adaptations of this bee group to their natural environment, thus contributing to the conservation and sustainable management of Meliponini species. Here, was analysed the natural thermal conditions in nests of Melipona subnitida in the Caatinga biome and investigated the thermal tolerance of workers bees of this bee species. The present study was performed at the Experimental Field Station Rafael Fernandes and at the Laboratory of Behavioural Ecology, both belonging to the Federal Brazilian University at Mossoro-RN. For our investigation of the mechanisms of thermoregulation, we used two nests of M. subnitida, the first being a wooden box commonly used in stingless bee-keeping containing an intact bee colony, the second an abandoned nest localized in a living tree. The latter nest was used to evaluate the level of thermic insulation provided in a natural nesting cavity. Temperature data were registered at different areas inside the nests using thermo-sensors connected to data-loggers. For the determination of the thermal tolerance of M. subnitida adults, groups of workers were kept at different temperatures inside BOD incubators, supplied with sugar water and, in some experimental groups, water. The temperature inside the nests closely followed the variations in ambient temperature. Even so, the temperature in the brood area was more stable than that of the other investigated thermal environments. During our study, the temperature in the brood area varied between 27-33°C, and reached maximum values of 4° above outside environmental temperature. Both the reduced thermal variation and the temperature increase above ambient temperature in the brood area point to some form of active thermoregulation in M. subnitida. Further, thermal oscillations inside the tree trunk were smaller compared to those registered in the outside environment. This indicates that the nesting cavity provides some form of thermal insulation, probably related to the thickness of the wood around the cavity. Concerning the thermal tolerance of workers of M. subnitida, we found mortality rates of 100% at temperatures above 42°C and below 0°C, indicating these temperatures as lethal for this stingless bee species. The thermal tolerance (50% mortality) of workers was between 5 and 40°C. The access to water during the experiments increased the thermal tolerance of workers exposed to high temperatures / A tolerância térmica e a termorregulação em abelhas sem ferrão (Hymenoptera, Apidae, Meliponini) são aspectos importantes para entender a evolução da sua socialidade. Além de contribuir com informações acerca da adaptação das espécies ao seu habitat natural, e com a conservação e manejo sustentável das espécies. No presente estudo analisamos as condições térmicas naturais de ninhos de Melipona subnitida no bioma Caatinga e investigamos a faixa de tolerância térmica de abelhas operárias desta espécie. O estudo foi realizado na Fazenda Experimental Rafael Fernandes e no Laboratório de Ecologia Comportamental, ambos pertencentes à Universidade Federal Rural do Semiárido em Mossoró-RN. Para o estudo da termorregulação foram utilizados dois ninhos de M. subnitida: um habitado mantido em uma caixa racional de madeira e outro desabitado localizado em uma árvore viva. Este último foi utilizado para analisar o nível de isolamento térmico conferido pela cavidade de nidificação em ambiente natural. Dados de temperatura foram coletados em diferentes áreas no interior dos ninhos através de sensores conectados a data loggers. Para determinar a tolerância térmica, operárias foram submetidas a diferentes temperaturas em uma estufa incubadora, supridas com xarope de açúcar e, em alguns grupos experimentais, com água. Verificamos que a temperatura dos ninhos seguiu as variações da temperatura ambiental. Porém, a temperatura na área de cria foi mantida relativamente constante em uma faixa de 27-33°C e chegou a ficar cerca de 4° a mais que a temperatura ambiente. A manutenção de temperaturas constantes na área de cria e o aumento da temperatura em relação ao ambiente indicam que, de alguma forma, as operárias de M. subnitida regulam ativamente a temperatura nesta área. A amplitude térmica no interior da árvore foi menor do que a amplitude térmica ambiental, indicando que cavidade de nidificação confere algum isolamento térmico, provavelmente devido a espessura da madeira da árvore onde fica a cavidade. Com respeito à tolerância térmica de operárias de M. subnitida, foi observada a taxa de mortalidade de 100% dos indivíduos em temperatura acima de 42°C e abaixo de 0°, indicando que estas são temperaturas letais para indivíduos adultos dessa espécie de abelhas sem ferrão. Enquanto, a faixa de tolerância térmica das operárias (mortalidade 50%) ficou entre 5° e 40ºC. O acesso à água durante os experimentos aumentou a tolerância térmica das abelhas em temperaturas altas

Orientador: Rogério Lopes Vieites / Banca: Regina Marta Evangelista / Banca: Ben Hur Mattiuz / Banca: Luciana Manoel / Banca : André José de Campos / Resumo: Este trabalho teve como objetivo prolongar a vida útil de ameixas cv. Gulfblaze, provenientes de Holambra II - SP, com o emprego da irradiação gama, embalagem e o uso de condicionamento térmico em frutos refrigerados. Foram realizados dois experimentos: Experimento 1 - frutos irradiados (0,0; 0,4; 0,6; 0,8; 1,0kGy) submetidos à atmosfera modificada passiva e Experimento 2 - frutos submetidos ao condicionamento térmico (10±2°C por 2 dias), irradiados (0,0; 0,4; 0,6; 0,8; 1,0kGy) submetidos à atmosfera modificada passiva. Os frutos foram selecionados e embalados para então serem irradiados no IPEN, localizado em São Paulo - SP. Logo após seguiram para o Laboratório de Frutas e Hortaliças, pertencente ao Departamento de Gestão e Tecnologia Agroindustrial, da Faculdade de Ciências Agronômicas - UNESP - Câmpus de Botucatu, SP. Nos dois experimentos, os frutos após os tratamentos, foram armazenados em B.O.D. a 0±2°C e com 90±5% de UR por 35 dias. As avaliações foram realizadas a cada cinco dias, durante 35 dias de armazenamento. As alterações na qualidade pós-colheita foram detectadas por meio das análises de perda de massa fresca, firmeza, pH, acidez titulável, sólidos solúveis, razão SS/AT "Ratio" açúcares redutores, açúcares totais, vitamina C total, pigmentos, compostos fenólicos totais e taxa de respiração. O delineamento estatístico empregado foi inteiramente casualizado com três repetições por tratamento para cada um dos oito tempos de avaliação, utilizando-se o Teste de Tukey a 5% de probabilidade. Nas condições em que os experimentos foram realizados, os resultados permitem concluir que, os frutos da ameixeira 'Gulfblaze' são resistentes à refrigeração (0±2°C), não apresentando sintomas de injúria até os 35 dias de armazenamento. O condicionamento levou a uma aceleração do amadurecimento, mostrando-se não recomendável para essa variedade de ameixas / Abstract: The present work aims at protracting the lifespan of plums cv. Gulfblaze, originating from Holambra II, São Paulo, by application of gamma irradiation, packaging and the use of thermal conditioning on cold fruits. Two experiments were made: Experiment 1. irradiated fruits (0,0; 0,4; 0,6; 0,8; 1,0KGy) undergo a passive modified atmosphere and Experiment 2. fruits undergo thermal conditioning (10±2°C for 2 days), irradiation (0,0; 0,4; 0,6; 0,8; 1,0KGy), and are subjected to passive modified atmosphere. The fruits were selected and packed, and then irradiated at IPEN, located in São Paulo - SP. Thereupon, they were directed to the Laboratory of Fruit and Vegetables from the Department of Management and Agribusiness Technology of the Agronomic Sciences Faculty - UNESP - Botucatu, Brazil. In both experiments, after the treatment the fruits were stored in B.O.D at 0±2°C with 90±5% RH for 35 days. Evaluations were conducted every five days, for the 35 days of storage. Alterations on post-harvest quality were detected by means of analysis of fresh mass loss, consistency (firmness), pH, total titratable acidity, soluble solids, 'Ratio' (SS/TTA), reducing sugar content, total reducing sugar, vitamin C total, pigment, phenolic compounds and respiratory rates. The employed statistical design was thoroughly randomized with three replications per treatment for each of the eight evaluations using the Turkey's Test to 5% of probability. Under the circumstances in which the experiments were performed, the results allow for the conclusion that 'Gulfblaze' plum fruits are resistant to refrigeration (0±2°C), with no symptoms of injury during the 35 days at storage. The conditioning led to ripening acceleration, proving to be not advisable for this sort of plum. The use of gamma radiation did not lead to improvement, regardless of the applied dose / Doutor

Low oxygen tolerances of ten fishes were estimated using an original nitrogen cascade design, and reciprocally transformed to express responses as ventilated volume necessary to satisfy minimal oxygen demand (L·mg O2^-1). Values ranged from 0.52 to 5.64 L·mg^-1 and were partitioned into three statistically distinct groups. Eight stream fishes showed moderately high tolerances reflecting metabolic adaptations associated with stream intermittency. Juvenile longear sunfish and two mollies comprised the second group. High tolerance of hypoxia may allow juvenile sunfish to avoid predation, and mollies to survive harsh environmental oxygen regimens. The sheepshead minnow was the most tolerant species of low oxygen, of those examined, explaining its presence in severely hypoxic environments.