Aquatic Surface Respiration Research Articles

Functional differentiation in the anterior gills of the aquatic air-breathing fish, Trichogaster leeri

The fish gill is a multifunctional organ responsible for gas exchange and ionic regulation. It is hypothesized that both morphological and functional differentiation can be found in the gills of the aquatic air-breathing fish, Trichogaster leeri. To test this, we used the air-breathing fish, Trichogaster leeri, to investigate various morphological/functional parameters. First, we evaluated the importance of performing the aquatic surface respiration behavior in T. leeri. A reduced survival rate was observed when fish were kept in the restrained cages in hypoxic conditions. On the gross anatomy of gills, we found evidence of both morphological and functional modification in the first and the second gills and are responsible for ionic regulation. There were large-bore arterioarterial shunts in the fourth gill arch. It is specialized for the transport of oxygenated blood and is less responsive to environmental stress. In addition, the anterior and the posterior gills differed in the Na(+), K(+)-ATPase activity upon ionic stresses. That is, only the Na(+), K(+)-ATPase activity of the anterior two gills was up-regulated significantly in the deionized water. Lastly, we found that the number of mitochondria-rich cells in the first and the second gills increased following ionic stress and no difference was found in the third and the fourth gills following such an exposure. These results supported the hypothesis that there are morphological and functional differences between anterior and posterior gill arches within the air-breathing Trichogaster leeri. In contrast, no significant difference was found among gills in gross anatomy, filament density and Na(+), K(+)-ATPase activity in the non-air-breather, Barbodes schwanenfeldi.

Swimming in the upside down catfishSynodontis nigriventris: it matters which way is up

Synodontis nigriventris is a surface-feeding facultative air-breather that swims inverted with its zoological ventral side towards the water surface. Their near-surface drag is about double the deeply submerged drag (due to wave drag) and roughly twice the sum of frictional and pressure drags. For streamlined technical bodies, values of wave drag augmentation near the surface may be five times the deeply submerged values. However, the depth dependence of drag is similar for fish and streamlined technical bodies, with augmentation vanishing at about 3 body diameters below the surface. Drag ;inverted' is approximately 15% less than that ;dorsal side up' near the surface. Consistent with this, at any given velocity, tailbeat frequency is lower and stride length higher for inverted swimming in surface proximity (P<0.05). Deeply submerged, there are no significant differences in drag and kinematics between postures (P>0.05). At the critical Froude number of 0.45, speeds in surface proximity correspond to prolonged swimming that ends in fatigue. To exceed these speeds, the fish must swim deeply submerged and this behaviour is observed. Inverted swimming facilitates efficient air breathing. Drag dorsal side up during aquatic surface respiration is 1.5 times the value for the inverted posture. Fast-starts are rectilinear, directly away from the stimulus. Average and maximum velocity and acceleration decrease in surface proximity (P<0.05) and are higher inverted (maximum acceleration: 20-30 m s(-2); P<0.05) and comparable to locomotor generalists (e.g. trout). Mechanical energy losses due to wave generation are about 20% for inverted and 40% for dorsal side up, and lower than for trout fast-starting in shallow water (70% losses); bottom effects and large amplitude C-starts (c.f. relatively low amplitude rectilinear motions in S. nigriventris) enhance resistance in trout. S. nigriventris probably evolved from a diurnal or crepuscular 'Chiloglanis-like' benthic ancestor. Nocturnality and reverse countershading likely co-evolved with the inverted habit. Presumably, the increased energy cost of surface swimming is offset by exploiting the air-water interface for food and/or air breathing.

Survival in an extreme habitat: the roles of behaviour and energy limitation

Extreme habitats challenge animals with highly adverse conditions, like extreme temperatures or toxic substances. In this paper, we report of a fish (Poecilia mexicana) inhabiting a limestone cave in Mexico. Several springs inside the cave are rich in toxic H(2)S. We demonstrate that a behavioural adaptation, aquatic surface respiration (ASR), allows for the survival of P. mexicana in this extreme, sulphidic habitat. Without the possibility to perform ASR, the survival rate of P. mexicana was low even at comparatively low H(2)S concentrations. Furthermore, we show that food limitation affects the survival of P. mexicana pointing to energetically costly physiological adaptations to detoxify H(2)S.

Hypoxia and the antipredator behaviours of fishes.

Hypoxia is a phenomenon occurring in marine coastal areas with increasing frequency. While hypoxia has been documented to affect fish activity and metabolism, recent evidence shows that hypoxia can also have a detrimental effect on various antipredator behaviours. Here, we review such evidence with a focus on the effect of hypoxia on fish escape responses, its modulation by aquatic surface respiration (ASR) and schooling behaviour. The main effect of hypoxia on escape behaviour was found in responsiveness and directionality. Locomotor performance in escapes was expected to be relatively independent of hypoxia, since escape responses are fuelled anaerobically. However, hypoxia decreased locomotor performance in some species (Mugilidae) although only in the absence of ASR in severe hypoxia. ASR allows fish to show higher escape performance than fish staying in the water column where hypoxia occurs. This situation provides a trade-off whereby fish may perform ASR in order to avoid the detrimental effects of hypoxia, although they would be subjected to higher exposure to aerial predation. As a result of this trade-off, fishes appear to minimize surfacing behaviour in the presence of aerial predators and to surface near shelters, where possible. For many fish species, schooling can be an effective antipredator behaviour. Severe hypoxia may lead to the disruption of the school unit. At moderate levels, hypoxia can increase school volume and can change the shuffling behaviour of individuals. By altering school structure and dynamics, hypoxia may affect the well functioning of schooling in terms of synchronization and execution of antipredator manoeuvres. School structure and volume appear to be the results of numerous trade-offs, where school shape may be dictated by the presence of predators, the need for energy saving via hydrodynamic advantages and oxygen level. The effects of hypoxia on aquatic organisms can be taxon specific. While hypoxia may not necessarily increase the vulnerability of fish subject to predation by other fish (since feeding in fish also decreases in hypoxia), predators from other taxa such as birds, jellyfish or aquatic mammals may take advantage of the detrimental effects of hypoxia on fish escape ability. Therefore, the effect of hypoxia on fish antipredator behaviours may have major consequences for the composition of aquatic communities.

Brood protection at a cost: mouth brooding under hypoxia in an African cichlid

This study quantifies the behavioral response of the widespread mouth brooding African cichlid Pseudocrenilabrus multicolor victoriae to progressive hypoxia. We exposed four gender/stage classes of P. multicolor (males, brooding females, females that had just released young, and non-brooding females) to progressive hypoxia and recorded the percent time spent using aquatic surface respiration (surface skimming, ASR) and gill ventilation rates. This was done for fish collected from three sites in Uganda (lake, swamp, and river) after long-term acclimation to normoxia. There was no effect of site of origin on response to hypoxia, but ASR thresholds did differ between gender/stage classes. The oxygen level (threshold) at which spent 10, 50, and 90% of their time at the surface using ASR was much higher for brooding females than for males, whereas ASR thresholds did not differ between non-brooding females and males. Similarly, the level at which ASR was initiated was much higher in brooding females than males, but did not differ between males and non-brooders, or between males and females than had just released young. The rate of gill ventilation dropped significantly in males and all stages of females after initiation of ASR, suggesting that surface skimming increases efficiency of oxygen acquisition. These results suggest that mouth brooding in female P. multicolor ASR improves oxygen uptake but imposes a cost in terms of time spent at the water surface, and this may affect maternal predation risk in low-oxygen habitats.

Behavioural responses of a south‐east Australian floodplain fish community to gradual hypoxia

Summary1. Hypoxic conditions occur frequently during hot, dry summers in the small lentic waterbodies (billabongs) that occur on the floodplains of the Murray‐Darling River system of Australia. Behavioural responses to progressive hypoxia were examined for the native and introduced floodplain fish of the Ovens River, an unregulated tributary of the Murray River in south‐east Australia.2. Given the high frequency of hypoxic episodes in billabongs on the Ovens River floodplain, it was hypothesised that all species would exhibit behaviours that would confer a degree of hypoxia‐tolerance. Specifically, it was hypothesised that as hypoxia progressed, gill ventilation rates (GVRs) would increase and aquatic surface respiration (ASR) would become increasingly frequent. Fish were subjected to rapid, progressive hypoxia from normoxia to anoxia in open tanks.3. All tested species exhibited behaviours consistent with their use of potentially hypoxic habitats. As hypoxia progressed, GVRs increased and all species, with the exception of oriental weatherloach, began to switch increasingly to ASR with 90% of individuals using ASR at various oxygen concentrations below 1.0 mg O2 L−1. Australian smelt, redfin perch and flat‐headed galaxias were the first three species to rise to ASR, with 10% of individuals using ASR by 2.55, 2.29 and 2.21 mg O2 L−1 respectively. Goldfish and common carp were the last two species to rise to ASR, with 10% of individuals using ASR by 0.84 and 0.75 mg O2 L−1 respectively. In contrast to other species, oriental weatherloach largely ceased gill ventilation and used air‐gulping as their primary means of respiration during severe hypoxia and anoxia.4. Australian smelt, redfin perch and flat‐headed galaxias were unable to maintain ASR under severe hypoxia, and began exhibiting erratic movements, termed terminal avoidance behaviour, and loss of equilibrium. All other species continued to use ASR through severe hypoxia and into anoxia. Following a rise to ASR, GVRs either remained steady or decreased slightly indicating partial or significant relief from hypoxic stress for these hypoxia‐tolerant species.5. Behavioural responses to progressive hypoxia amongst the fish species of the Ovens River floodplain indicate a generally high level of tolerance to periodic hypoxia. However, species‐specific variation in hypoxia‐tolerance may have implications for community structure of billabong fish communities following hypoxic events.

Adaptations of fish species to oxygen depletion in a central Amazonian floodplain lake

Pronounced seasonal and daily oxygen concentration changes are characteristic for Amazonian floodplain lakes. Studies on the fish fauna of the Lago Camaleao, Solimoes River, Amazonas, Brazil, showed several fish species which are able to survive prolonged periods of heavy hypoxia. Twenty species belonging to eight families were observed in the laboratory in order to determine their respiratory adaptations to hypoxic conditions and oxygen concentrations at which the fish present respiratory adaptations. Finally, the fish species were distributed throughout the habitats of Lake Camaleao according to their adaptation responses. Ten fish species used the surface water for aquatic surface respiration, four species used atmospheric oxygen for aerial respiration, four species used oxygen supplied by the exudation of the roots of floating macrophytes and two exhibited a high tolerance to hypoxic conditions, and well-developed physiological biochemical mechanisms. The fish fauna is well adapted to low oxygen concentrations. The large variety of morpho-anatomical adaptations associated with biochemical and physiological mechanisms to tolerate hypoxic and anoxic conditions enable the 20 fish species to exploit several habitats of Lago Camaleao, such as floating aquatic macrophyte meadows, open water and near the shoreline.

The role of branchial and orobranchial O2 chemoreceptors in the control of aquatic surface respiration in the neotropical fish tambaqui(Colossoma macropomum): progressive responses to prolonged hypoxia

The present study examined the role of branchial and orobranchial O(2) chemoreceptors in the cardiorespiratory responses, aquatic surface respiration (ASR), and the development of inferior lip swelling in tambaqui during prolonged (6 h) exposure to hypoxia. Intact fish (control) and three groups of denervated fish (bilateral denervation of cranial nerves IX+X (to the gills), of cranial nerves V+VII (to the orobranchial cavity) or of cranial nerves V alone), were exposed to severe hypoxia (Pw(O)2=10 mmHg) for 360 min. Respiratory frequency (fr) and heart rate (fh) were recorded simultaneously with ASR. Intact (control) fish increased fr, ventilation amplitude (V(AMP)) and developed hypoxic bradycardia in the first 60 min of hypoxia. The bradycardia, however, abated progressively and had returned to normoxic levels by the last hour of exposure to hypoxia. The changes in respiratory frequency and the hypoxic bradycardia were eliminated by denervation of cranial nerves IX and X but were not affected by denervation of cranial nerves V or V+VII. The V(AMP) was not abolished by the various denervation protocols. The fh in fish with denervation of cranial nerves V or V+VII, however, did not recover to control values as in intact fish. After 360 min of exposure to hypoxia only the intact and IX+X denervated fish performed ASR. Denervation of cranial nerve V abolished the ASR behavior. However, all (control and denervated (IX+X, V and V+VII) fish developed inferior lip swelling. These results indicate that ASR is triggered by O(2) chemoreceptors innervated by cranial nerve V but that other mechanisms, such as a direct effect of hypoxia on the lip tissue, trigger lip swelling.

Tribute to R. G. Boutilier: The effect of size on the physiological and behavioural responses of oscar,Astronotus ocellatus, to hypoxia

The physiological and behavioural responses of two size groups of oscar (Astronotus ocellatus) to hypoxia were studied. The physiological responses were tested by measuring M(O(2)) during decreasing environmental oxygen tensions. Larger oscars were better able to maintain oxygen consumption during a decrease in P(O(2)), regulating routine M(O(2)) to a significantly lower P(O(2)) threshold (50 mmHg) than smaller oscars (70 mmHg). Previous studies have also demonstrated a longer survival time of large oscars exposed to extreme hypoxia, coupled with a greater anaerobic enzymatic capability. Large oscars began aquatic surface respiration (ASR) at the oxygen tension at which the first significant decrease in M(O(2)) was seen (50 mmHg). Interestingly, smaller oscars postponed ASR to around 22 mmHg, well beyond the P(O(2)) at which they switched from oxyregulation to oxyconformation. Additionally, when given the choice between an hypoxic environment containing aquatic macrophyte shelter and an open normoxic environment, small fish showed a greater preference for the hypoxic environment. Thus shelter from predators appears particularly important for juveniles, who may accept a greater physiological compromise in exchange for safety. In response to hypoxia without available shelter, larger fish reduced their level of activity (with the exception of aggressive encounters) to aid metabolic suppression whereas smaller oscars increased their activity, with the potential benefit of finding oxygen-rich areas.

The effect of hypoxia on locomotor performance and behaviour during escape in Liza aurata

Escape performance was investigated in the golden grey mullet Liza aurata exposed to various levels of oxygen: &gt;85 (i.e. normoxia), 50, 20 and 10 % air saturation. Since the golden grey mullet performed aquatic surface respiration when air saturation approached 15–10 %, escape performance was tested at 10 % air saturation with and without access to the surface (10 % S and 10 % C, respectively). Various locomotor and behavioural variables were measured, such as cumulative distance, maximum swimming speed, acceleration, responsiveness (per cent of responding fish), response latency and directionality. Golden grey mullet showed a decrease in responsiveness when the oxygen level was reduced to 10 % air saturation, whether the surface access was obstructed or not. Hypoxia did not have any effect on the response latency. Cumulative distance and maximum swimming speed over a fixed time were significantly different between normoxic conditions and 10 % C, while no differences were found in maximum acceleration. While the fish's ‘C‐bend’ was mainly directed away from the stimulus in normoxia, the proportion of away and towards ‘C‐bend’ was random when the oxygen was ≤20 % air saturation. This suggested an impairment of the left‐right discrimination at the initiation of the fast start. Hypoxia affected golden grey mullet escape performance mainly through an impairment of responsiveness and directionality, while locomotor performance was affected only in severe hypoxia when the surface was obstructed. The study showed that, in addition to forcing the fish to the surface as shown by previous studies, hypoxia may also reduce fish elusiveness facing a predator by directly impairing its escape performance.

Reflex Cardioventilatory Responses to Hypoxia in the Flathead Gray Mullet (Mugil cephalus) and Their Behavioral Modulation by Perceived Threat of Predation and Water Turbidity

In hypoxia, gray mullet surface to ventilate well-oxygenated water in contact with air, an adaptive response known as aquatic surface respiration (ASR). Reflex control of ASR and its behavioral modulation by perceived threat of aerial predation and turbid water were studied on mullet in a partly sheltered aquarium with free surface access. Injections of sodium cyanide (NaCN) into either the bloodstream (internal) or ventilatory water stream (external) revealed that ASR, hypoxic bradycardia, and branchial hyperventilation were stimulated by chemoreceptors sensitive to both systemic and water O2 levels. Sight of a model avian predator elicited bradycardia and hypoventilation, a fear response that inhibited reflex hyperventilation following external NaCN. The time lag to initiation of ASR following NaCN increased, but response intensity (number of events, time at the surface) was unchanged. Mullet, however, modified their behavior to surface under shelter or near the aquarium edges. Turbid water abolished the fear response and effects of the predator on gill ventilation and timing of ASR following external NaCN, presumably because of reduced visibility. However, in turbidity, mullet consistently performed ASR under shelter or near the aquarium edges. These adaptive modulations of ASR behavior would allow mullet to retain advantages of the chemoreflex when threatened by avian predators or when unable to perceive potential threats in turbidity.

Hypoxia and interdemic variation in Poecilia latipinna

Variation in respiratory traits was quantified between two populations of the sailfin molly Poecilia latipinna(one from a periodically hypoxic salt marsh, Cedar Key, and one from a chronically normoxic river site, Santa Fe River). Two suites of characters were selected: traits that may show both short‐term acclimation response and interdemic variation in acclimation response (metabolic rate, critical oxygen tension and respiratory behaviour), and those that are not likely to respond to short‐term acclimation but may vary among populations (gill morphometric characters). Sailfin mollies from the salt marsh, acclimated to hypoxia (1 mg l−1, c. 20 mmHg) for 6 weeks, spent less time conducting aquatic surface respiration and had lower gill ventilation rates than hypoxia‐acclimated conspecifics from the well‐oxygenated river site. Poecilia latipinna acclimated to hypoxia exhibited a lower critical oxygen tension (Pc) than fish acclimated to normoxia; however, there was also a significant population effect. Poecilia latipinna from Cedar Key exhibited a lower Pc than fish from the Santa Fe River, regardless of acclimation. Cedar Key fish had a 14% higher mean gill surface area relative to fish from the Santa Fe River, a character that could account, at least in part, for their greater tolerance to hypoxia.

Acute Cu toxicity, metal bioaccumulation and ion loss in the Neotropical cyprinodontiform Jenynsia multidentata

The acute toxicity of Cu, metal bioaccumulation and ion loss in the cyprinodontiform Jenynsia multidentata , a highly eurihaline Neotropical freshwater fish of wide distribution in the Rio de la Plata basin, was established during a 96 h static exposure. The median lethal concentration at 96 h was 229 µg Cu l -1 . The effect of CuSO 4 5H 2 O was tested in natural freshwater in two-liter Pyrex glass chambers at controlled temperature, with natural light and artificial aeration. During the first hours of exposure to concentrations above 130 µg Cu l -1 , an increase in aquatic surface respiration, air gulping and erratic swimming were observed, showing evidence of the affection of the respiratory system. The concentration of Cu, Na and K in the whole body burden at the end of each experiment showed by correlation analysis Cu bioaccumulation and loss of Na + and K + . The concentration of Cu in water was positively correlated with its bioaccumulation (r=0.79, p=0.06), and negatively correlated with the whole body burden of K + (r=-0.84, p=0.037). K + loss was positively correlated with Na + loss (r=0.88, p=0.02). Cu LC50 for this cyprinodontiform seems rather low when compared to fishes often utilized in toxicity tests

The Effect of Gestational State on Oxygen Consumption and Response to Hypoxia in the Sailfin Molly, Poecilia latipinna

Metabolic activity in livebearing fishes increases with embryonic development so that embryos prior to parturition may have a higher mass-specific oxygen requirement than maternal tissues, temporarily increasing the total routine oxygen requirement of the female. We examined whether females of the livebearing poeciliid Poecilia latipinna (sailfin molly) increase their routine metabolic oxygen consumption during development of their broods. We also quantified effects of gestation on time allocation to aquatic surface respiration (ASR) under hypoxic conditions. Mass-adjusted routine metabolic rate (RMR) of female mollies showed a significant increase during late gestation. The RMR of males did not differ from females that were in their early or mid stage of gestation, but was lower than females in late gestation. Gestating females spent approximately 27% more time conducting ASR than non-gestating females when exposed to chronic hypoxia (1 mg l−1), further supporting a brood-related increase in oxygen demand. Increased time allocation to ASR may directly affect maternal predation risk in low-oxygen conditions.

Hypoxia tolerance of the mummichog: the role of access to the water surface

Low dissolved oxygen (DO) had a significant effect on specific growth rate (GS), length increment (IL) and haematocrit (Hct) of the mummichog Fundulus heteroclitus. Regardless of access to the water surface, F. heteroclitus maintained high growth rates (GS and IL) at DO concentrations as low as 3 mg O2 l−1. With access to the water surface, both GS and IL of F. heteroclitus decreased by c. 60% at 1·0 mg O2 l−1 compared to all higher DO treatments. When denied access to the water surface, a further decrease in GS (c. 90%) and IL (c. 75%) was observed at 1 mg O2 l−1. There was no effect of diel‐cycling DO (1–11 mg O2 l−1) with or without surface access on GS, IL or Hct of F. heteroclitus. Similar trends between GS and faecal production across DO treatments suggest that decreased feeding contributed significantly to the observed decrease in growth rate. Haematocrit was significantly elevated at 1 mg O2 l−1 for fish with and without access to the water surface. Increased Hct, however, was not sufficient to maintain high GS or IL at severely low DO. When permitted to respire in the surface layer, however, F. heteroclitus was capable of maintaining moderate growth rates at DO concentrations of 1 mg O2 l−1 (c. 15% saturation). Although aquatic surface respiration (ASR) was not quantified in this study, F. heteroclitus routinely swam in contact with the water surface and performed ASR at DO concentrations ≤3 mg O2 l−1. No hypoxia‐related mortality was observed in any DO or surface access treatment for as long as 9 days. This study demonstrates that surface access, and thus potential for ASR, plays an important role in providing F. heteroclitus substantial independence of growth rate over a wide range of low DO conditions commonly encountered in shallow estuarine environments.

Susceptibility of the Amazonian fish, Colossoma macropomum (Serrasalminae), to short-term exposure to nitrite

Nitrite (NO 2 −) is toxic to fish. High levels of NO 2 − may develop in natural aquatic environments or in aquaculture systems, a situation that is aggravated in tropical regions by high temperatures and low dissolved oxygen. The toxicity of NO 2 − was evaluated in the Amazonian fish, Colossoma macropomum to define the environmental quality standards and management of culture system for this species. The acute toxicity of NO 2 − was tested using a renewal bioassay system and a series of increasing NO 2 − concentrations up to 0.4 mM NO 2 − (5.6 mg l −1). Blood samples were taken after a 96-h exposure to NO 2 − to determine the hematological parameters, methaemoglobin (MetHb) concentration and plasma nitrite bioaccumulation. The 96-h LC 50 was calculated as 0.13±0.06 mM NO 2 − (1.82±0.98 mg l −1), indicating high sensitivity of this species to nitrite. Nitrite bioaccumulation resulted in methaemoglobinemia (66–76%) and hemolytic anemia (depression in total hemoglobin (Hb) concentration, hematocrit (Ht) and red blood cells (RBC)), which compromise the transport of O 2 through the blood from the gills to the tissues. The increase of mean corpuscular Hb concentration in fish exposed to 0.04 and 0.2 mM NO 2 − suggested changes in the ionic transport across the erythrocyte membrane. The absence of ecomorphological responses such as lip formation and aquatic surface respiration (ASR) during NO 2 − exposure indicates that the mechanism involved in nitrite-induced hypoxia differs from that induced by environmental hypoxia. These findings reveal that intensive aquaculture systems of C. macropomum should be managed so as to avoid even low levels of NO 2 −, since the effects of nitrite may compromise the fish's performance in an environment in which high temperature and daily fluctuations in dissolved oxygen may aggravate nitrite intoxication.

Behavioral Responses of Mosshead and Woolly Sculpins to Increasing Environmental Hypoxia

Behavioral responses of the rocky intertidal mosshead sculpin (Clinocottus globiceps) and woolly sculpin (Clinocottus analis) to increasing environmental hypoxia (low PO2) were observed in a seawater aquarium with a depth gradient. The experimental design allowed observation of the response of these animals to encroaching environmental hypoxia. We observed three behaviors by which the fish dealt with hypoxia: emergence from substrate (EFS), first avoidance response (FAR), and aquatic surface respiration (ASR). With respect to EFS and FAR, mosshead sculpins were more labile in their responses than woolly sculpins. However, the mean PO2 at which ASR was initiated was statistically indistinguishable between species. We suggest that the differences we observed represent alternate behaviors by which these related species deal with the trade-off imposed by the simultaneous needs to avoid predation and optimize respiration. We further suggest that these alternate behaviors have evolved around a conserved physiological constraint, the PO2 at which ASR must be performed.

Parental Responses to Changes in Costs and Benefits Along an Environmental Gradient

We evaluated the effects of dissolved oxygen on offspring survival, parental costs, and the pattern of parental care in Florida flagfish, Jordanella floridae (Cyprinodontidae). Specifically, we quantified (1) embryonic development and survival in the absence of parental care, (2) behavior of non-reproductive adults, and (3) behavior of parental males across a gradient in dissolved oxygen. Embryo developmental rates and survivorship increased with dissolved oxygen, with a relatively sharp increase in survival between medium and high oxygen treatments. Non-reproductive adults increased their frequency of aquatic surface respiration, reduced overall activity, and increased opercular beat rate as oxygen declined, suggesting increased costs of activity with reduced oxygen. Taking these cost measures together, costs appear to increase slowly as oxygen starts to decline and then increase sharply as conditions approach hypoxia. In contrast, parental effort increased gradually with dissolved oxygen. We conclude that the increase in care from low to medium oxygen primarily results from a sharp decline in physiological costs, whereas the continued increase in care from medium to high oxygen primarily results from an increase in offspring value. In addition, our results highlight that the benefits of fanning for offspring are not well understood and that they may increase with oxygen, contrary to what has been previously assumed.

Dissolved oxygen dynamics in salt marsh pools and its potential impacts on fish assemblages

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 258:223-232 (2003) - doi:10.3354/meps258223 Dissolved oxygen dynamics in salt marsh pools and its potential impacts on fish assemblages Kelly J. Smith1, Kenneth W. Able2,* 1Department of Biology, University of North Florida, 4567 St. Johns Bluff Road South, Jacksonville, Florida 32224-2661, USA 2Marine Field Station, Institute of Marine and Coastal Sciences, Rutgers University, 800 c/o 132 Great Bay Boulevard, Tuckerton, New Jersey 08087-2004, USA *Corresponding author. Email: able@imcs.rutgers.edu ABSTRACT: In order to determine the dynamics of dissolved oxygen (DO) in salt marsh pools and its effect on their respective fish assemblages, DO was measured in 5 high-salinity pools in a Spartina alterniflora marsh in southern New Jersey over ten 24 h periods, from 2 July to 22 October 1990, to determine daily and monthly fluctuations. Typically, DO peaked at approximately 16:00 h, and reached a minimum by about 05:00 h. The greatest variation occurred in mid-July, when DO ranged from over 20 ppm at midday, to 0 ppm in the early morning. From mid- to late August, DO remained at very low concentrations (<1.0 ppm) for long periods (11.7 ± 1.7 h). DO concentrations varied among marsh pools, but there was no interaction between pool and time of day. The young-of-the-year (YOY) of the dominant 5 species of fishes in these pools were tested for tolerance and behavioral responses to low DO in laboratory aquaria. Fundulus heteroclitus survived the longest at low DO, and Menidia menidia was least tolerant. Aquatic surface respiration (ASR) was the primary behavioral response to low DO for all species tested. All species, including Cyprinodon variegatus, Lucania parva, and M. beryllina, survived at DO < 0.5 ppm when they used ASR; however, when fish were denied access to the air-water interface, only F. heteroclitus was able to survive more than 1 h. All species initiated ASR at ca. 1 ppm, with the exception of M. menidia, which began ASR at 2.6 ppm and survived only at higher concentrations of DO. In summary, although the salt marsh pools showed extreme diurnal variability in DO, with rapid drops from supersaturation to anoxic conditions, all of the fish species, with the exception of M. menidia, were well adapted to survive these fluctuations. This lack of tolerance to low DO by M. menidia may seasonally limit its occurrence in marsh pools, but this is not the case for the congener M. beryllina, or the other resident fishes. KEY WORDS: Dissolved oxygen · Salt marshes · Pools · Killifishes · Silversides · Young-of-the-year Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 258. Online publication date: August 29, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Physiological refugia: swamps, hypoxia tolerance and maintenance of fish diversity in the Lake Victoria region

In Lake Nabugabo, Uganda, a satellite of Lake Victoria, ≈50% of the indigenous fishes disappeared from the open waters subsequent to the establishment of the introduced predatory Nile perch, Lates niloticus. This pattern is similar to the faunal loss experienced in the much larger Lake Victoria. Several of these species persisted in wetland refugia (e.g. ecotonal wetlands, swamp lagoons); however, deep swamp refugia (habitats lying well within the dense interior of fringing wetlands), are available only to a subset of the basin fauna with extreme tolerance to hypoxia. Although air-breathers are common in deep swamp refugia; we also documented a surprisingly high richness and abundance of non-air-breathing fishes. We describe several mechanisms that may facilitate survival in deep swamp refugia including high hemoglobin concentration, high hematocrit, large gill surface area and a low critical oxygen tension ( P c). In addition, swamp-dwelling fishes showed lower P o 2 thresholds for onset of aquatic surface respiration than the lake-dwelling fishes. This suggests higher tolerance to hypoxia in the swamp fishes because they are able to withstand a lower oxygen tension before approaching the surface. We suggest that physiological refugia may be important in modulating the impact of Nile perch and indigenous fishes in the Lake Nabugabo region; this highlights the need to evaluate relative tolerance of introduced predators and indigenous prey to environmental stressors.