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How predators maximize energetic gains while minimizing the costs associated with exploiting heterogeneous prey remains a difficult ecological principle to test in natural systems. Deep‐diving, air‐breathing predators face conflicting demands of oxygen conservation to extend dive time and oxygen usage from the exercise required to find and capture prey. How predators balance these opposing factors is additionally complicated by prey patches that are heterogeneous spatially, temporally and in quality. Tags deployed on foraging fin whales revealed that deeper dives consisted of higher feeding rates (lunges/hr), as generally predicted by optimal foraging theory. By simultaneously measuring prey density and distribution in the local environment, we show that whales increased their dive depths in order to forage on the densest prey patches. Despite the increased travel time needed to find deeper prey during a breath‐hold dive, the increase in feeding rates of fin whales and modelled prey consumption quadrupled compared to shallow foraging. Because the cost of transport is low at this extreme in body size, we posit that feeding on the deep prey patches significantly increases the energetic efficiency of foraging. Given the increasing recognition that anthropogenic disturbance can curtail deep foraging dives in many cetacean species, endangered fin whales may be susceptible to significant energetic losses that may impact individual fitness and population health in some areas. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

High concentrations of environmental ammonia can cause reduced immunity and death in fish, causing enormous economic losses. Air‐breathing fish usually have a high ammonia tolerance and are very suitable for high‐density fish farming. However, research on the effects of environmental ammonia on air‐breathing fish immunity is lacking. Therefore, this study investigated the effects of environmental ammonia on the immunity of large‐scale loach (Paramisgurnus dabryanus) by exposing fish to 30 mmol/L NH4Cl solution and subsequently analyzing the changes in serum and liver immune indicators, including total protein, albumin, globulin, immunoglobulin (Ig) M, lysozyme, complement component (C) 3 and C4, heat shock protein (HSP) 70, HSP90, tumor necrosis factor (TNF)‐α, interleukin (IL)‐1β, IL‐6, and IL‐12. Results revealed that ammonia exposure significantly affected the total protein, albumin, globulin, IgM, complement C3 and C4, HSP70, HSP90, and inflammatory cytokine contents in the body, indicating that ammonia exposure induced a significant immune response and lowered bodily immunity. However, most of the immune indicators significantly decreased in the later stages of the experiment, suggesting a weakened immune response, which may be due to the species‐specific ammonia detoxification ability of large‐scale loach that reduces ammonia toxicity in the body. This study demonstrated the effects of high concentration of environmental ammonia on the immune response in Paramisgurnus dabryanus. Species‐specific ammonia detoxification strategies in P. dabryanus could weaken the immune response induced by high environmental ammonia.

Amphibian tadpoles are typically aquatic and constrained to freshwater throughout development. These circumstances change at metamorphosis, whereupon individuals may complete a partial or full habitat shift towards terrestriality and gain the capacity to transition between habitat types. In this study, we present evidence of striped marsh frog tadpoles, Limnodynastes peronii, resting out of the water on floating vegetation mats in freshwater ponds, despite being fully aquatic and at a developmental stage far proceeding metamorphosis. We propose that this behaviour may represent a form of adaptive beaching to obtain survival benefits that are derived from being out of the water column. In particular, this may be a behavioural tactic of habitat switching to avoid aquatic predators, such as the introduced mosquitofish, Gambusia holbrooki, or to access oxygen from the air when the water becomes hypoxic. The capacity for aquatic tadpoles to exploit temporary refuges outside the water challenges traditional assumptions about their strict dependence on being continuously submerged below the surface for survival. While our findings are preliminary and based on a small sample size, they suggest the aquatic tadpoles of our focal species and perhaps others are not as restricted to their natal waterbodies as previously thought and that they have the capacity to move into habitats above the water's surface for resource gain. Habitat switching is a behavioural or developmental process by which animals move from one habitat type to another for fitness gain. We provide observations of tadpoles of the striped marsh frog, Limnodynastes peronii, resting out of the water column on floating aquatic vegetation, despite being fully aquatic and at a developmental stage far proceeding metamorphosis. Given that the observed tadpoles were able to descend back into the water column when disturbed, we suggest that aquatic tadpoles of some species may participate in habitat switching behaviour, being able to move out of the water temporally for a benefit that may include predator avoidance or respiration.

1. Group-living is widespread among animals and comes with numerous costs and benefits. To date, research examining group-living has focused on trade-offs surrounding foraging, while other forms of resource acquisition have been largely overlooked. 2. Air-breathing has evolved in many fish lineages, allowing animals to obtain oxygen in hypoxic aquatic environments. Breathing air increases the threat of predation, so some species perform group air-breathing, to reduce individual risk. Within species, individual air-breathing can be influenced by metabolic rate as well as personality, but the mechanisms of group air-breathing remain unexplored. It is conceivable that keystone individuals with high metabolic demand or intrinsic tendency to breathe air may drive social breathing, especially in hypoxia. 3. We examine social air-breathing in African sharptooth catfish Clarias gariepinus,to determine whether individual physiological traits and spontaneous tendency to breathe air influence the behaviour of entire groups, and whether such influences vary in relation to aquatic oxygen availability. 4. We studied 11 groups of four catfish in a laboratory arena and recorded airbreathing behaviour, activity and agonistic interactions at varying levels of hypoxia. Bimodal respirometry was used to estimate individual standard metabolic rate (SMR) and the tendency to utilize aerial oxygen when alone. 5. Fish took more air breaths in groups as compared to when they were alone, regardless of water oxygen content, and displayed temporally clustered air-breathing behaviour, consistent with existing definitions of synchronous air-breathing. However, groups displayed tremendous variability in surfacing behaviour. Aggression by dominant individuals within groups was the main factor influencing air-breathing of the entire group. There was no association between individual SMR, or the tendency to obtain oxygen from air when in isolation, and group air-breathing. 6. For gariepinus, synchronous air-breathing is strongly influenced by agonistic interactions, which may expose subordinate individuals to risk of predation. Influential individuals exerted an overriding effect on risk-taking by the entire group, for reasons independent of their physiological oxygen requirements. Overall, this illustrates that social context can obscure interactions between an individual's physiological and behavioural traits and their tendency to take risks to obtain resources.

Dojo loach ( Misgurnus anguillicaudatus ) is an air-breathing fish species by using its posterior intestine to breathe on water surface. So far, the molecular mechanism about accessory air-breathing in fish is seldom addressed. Five cDNA libraries were constructed here for loach posterior intestines form T01 (the initial stage group), T02 (mid-stage of normal group), T03 (end stage of normal group), T04 (mid-stage of air-breathing inhibited group), and T05 (the end stage of air-breathing inhibited group) and subjected to perform RNA-seq to compare their transcriptomic profilings. A total of 92,962 unigenes were assembled, while 37,905 (40.77 %) unigenes were successfully annotated. 2298, 1091, and 3275 differentially expressed genes ( fn1 , ACE , EGFR , Pxdn, SDF, HIF, VEGF, SLC2A1 , SLC5A8 etc.) were observed in T04/T02, T05/T03, and T05/T04, respectively. Expression levels of many genes associated with air-breathing and nutrient uptake varied significantly between normal and intestinal air-breathing inhibited group. Intraepithelial capillaries in posterior intestines of loaches from T05 were broken, while red blood cells were enriched at the surface of intestinal epithelial lining with 241 ± 39 cells per millimeter. There were periodic acid-schiff (PAS)-positive epithelial mucous cells in posterior intestines from both normal and air-breathing inhibited groups. Results obtained here suggested an overlap of air-breathing and nutrient uptake function of posterior intestine in loach. Intestinal air-breathing inhibition in loach would influence the posterior intestine’s nutrient uptake ability and endothelial capillary structure stability. This study will contribute to our understanding on the molecular regulatory mechanisms of intestinal air-breathing in loach.

Modern concepts of operation of supersonic inlets of high-velocity air-breathing engines are analyzed. It is demonstrated that the flow in the engine duct becomes extremely complicated in off-design modes of inlet operation, which can lead to unpredictable consequences, in particular, to inlet unstart. The term “inlet unstart” is considered in the present paper as a synonym of the absence of theoretical understanding and prediction of gas-dynamic phenomena. Various approaches are proposed to ensure self-regulation of the inlet-combustor system for air-breathing engines. Possible directions of further research are indicated for the purpose of stable operation of inlets in a wide range of flight conditions.

A robust finite time sliding mode control strategy is proposed in this paper for a flexible air-breathing hypersonic vehicle （FAHV） model with aerodynamic parameter uncertainty. The strong coupling among the aerodynamics, the propulsion system and the flexibility effects makes the problera more challenging. Firstly, to reduce the complexity of the controller design, the FAHV model is transformed into three subsystems （velocity subsystem, altitude and flight path angle subsystem, attack of angle and pitch rate subsystem）. Secondly, based on super-twisting algorithm, a novel finite time disturbance observer and an improved sliding mode controller are designed to ensure the finite time stability of each subsystem. The proposed disturbance observer can estimate the uncertainty and the derivative of virtual control in finite time. Finally, simulation results are presented to show the precision and rapidness in tracking the reference trajectory and validate the effectiveness of the designed controller.

Clariidae, commonly referred as air-breathing or walking catfishes, are a family of catfish distributed in Africa, Asia Minor, the Indian subcontinent, and Southeast Asia. Some species are highly valuable as food fish. As part of ongoing ichthyofaunal surveys in the Central Mahakam River, East Kalimantan, Indonesia, we present our findings from Clarias specimens collected from Central Mahakam River. We document C. pseudonieuhofii Sudarto, Teugels & Pouyaud, 2004, in the Central Mahakam River, Kutai Kartanegara Regency, East Kalimantan, which is located approximately 1200 km from the type locality in West Kalimantan.

A method of increasing the efficiency of mixing in an air-breathing rocket engine is discussed. Three-dimensional simulations confirm the advantages of the proposed method based on using normal supply of products of incomplete combustion of a pasty propellant into the wake zone behind a bluff body in an air flow.