Terrestrial locomotion in the climbing perch, Anabas testudineus (Bloch) (Anabantidea, Pisces)

Climbing perches use the tail for forward propulsion when on land. The spiny gill covers are used to obtain purchase on the substratum. Unusually amongst teleosts, the opercular and subopercular bone are not bound strongly together into a single operculum. Instead they are joined only by a thin, flexible membrane, so that the fish has two sections of the gill cover hinged separately; the opercular on the suspensorium and the subopercular on the rearmost part of the lower jaw. The gill covers open very widely and the subopercular rotates ventrally as well as laterally. Two modes of locomotion are employed. Usually Anabus adopts a near-upright posture and alternately drives the left and right spiny suboperculars into the substratum, using the tail to vault over the subopercular (which acts in the manner of a short vaulting pole). During vigorous movement the fish may leave the substratum altogether during the vault. Fatigued fish, or fish which have fallen during climbing, move on their sides, using the tail for propulsion and a single spiny opercular which is repeatedly driven into the substratum. Maximum speeds observed on land corresponded to 1.8 body lengths S^?1. No evidence of involvement of the pelvic fins in locomotion was obtained; the pectorals seemed only to help in tilting the head from side to side and did not contribute significantly to forward propulsion. On mud and tree bark the fish were laterally unstable, often resting on their sides. Grassy substrata provided support and permitted a more upright posture. Slope climbing ability was restricted to 25° when climbing tree bark and 30° when climbing grass. Coupled with lateral instability these observations disqualify the species from any tree-climbing capacity. Anabas can climb vertical obstacles of at least half body length in height by pushing the head against the obstacle, using the spiny gill covers for purchase until one or other subopercular hooks over the top of the barrier. The subopercular is then used as a fulcrum for an upwards vault to clear the obstacle.     

Handling of ferric iron by branchial and intestinal epithelia of climbing perch (Anabas testudineus Bloch)

With a view to test how the branchial and intestinal tissues of fish, the two sites of metal acquisition, utilize the water-borne ferric [Fe(III)] iron and whether the accumulation of this form of iron influences cellular Na/K gradient in these tissues, the gills and intestines of climbing perch adapted to freshwater (FW) and acclimated to dilute seawater (20 ppt; SW) were analyzed for ouabain-sensitive Na+, K+-ATPase activity, Fe and electrolyte contents after loading a low (8.95 microM) or high dose (89.5 microM) of Fe(III) iron in the water. The SW gills showed higher levels of total Fe after treating with 8.95 microM of Fe(III) iron which was not seen in the FW gills. Na+, K+-ATPase activity, reflecting Na/K pump activity, showed an increase in the FW gills and not in the SW gills. Substantial increase in the branchial Na and K content was observed in the SW gills, but the FW gills failed to show such effects after Fe(III) loading. The total Fe content was declined in the FW intestine but not in the SW intestine. Water-borne Fe(III) iron decreased the activity of Na+, K+-ATPase in the SW intestine while not changing its activity in the FW intestine. The Na and K content in the FW intestine did not respond to Fe(III) iron exposure but showed a reduction in its Na levels in the SW intestine. The moisture content in the gills and intestines of both the FW and SW perch remained unaffected after Fe(III) loading. In FW fish, the plasma Na levels were decreased by a low dose of Fe(III) iron, though a high dose of Fe(III) iron was required in the SW fish for such an effect. Overall, the results for the first time provide evidence that gills act as a major site for Fe(III) iron absorption and accumulation during salinity acclimation which depends on a high cellular Na/K gradient.     

Morphology and vascular anatomy of the accessory respiratory organs of the air-breathing climbing perch, Anabas testudineus (Bloch)

The vascular organization and endothelial cell specialization of the air-breathing organs of Anabas testudineus were examined by light and scanning electron microscopy of fixed tissue and vascular corrosion replicas. The vessels supplying blood to the lining of paired suprabranchial chambers and the plicated labyrinthine organs within the chambers are tripartite, having a median artery and paired, lateral veins. Hundreds of respiratory islets, the functional units of gas exchange, cover the surfaces of both the chamber and labyrinthine organ. A median islet artery supplies the central aspect of each islet and gives rise to numerous short arterioles from which the transverse channels are formed. Transverse channels are parallel capillary-sized vessels that extend in two rows away from the medial arterioles and drain laterally into one of two lateral islet veins. Basally situated single rows of endothelial cells lining the transverse channels form thick, evaginated, tongue-like cytoplasmic processes that project freely into the lumen from the tissue side of the channel. Other thin, septate, cytoplasmic extensions of the same cells form valve-like septa that extend across the channel. Both the septa and tongue-like processes appear to direct the red blood cells to the epithelial side of the channel and thus decrease the diffusion distance between the air and red cell. A large sinusoidal space lies under the transverse channels and may support the channels and even elevate them during increased oxygen demand. The epithelium covering the transverse channels is smooth, which enhances air convection and minimizes unstirred layer effects. The epithelium between the channels contains microvilli that may serve to trap bacteria or particulates and to humidify the air chambers.     

Influence of habitat complexity on route learning among different populations of climbing perch (Anabas testudineus Bloch, 1792)

Animals use different behavioral strategies to maximize their fitness in the natural environment. Learning and memory are critical in this context, allowing organisms to flexibly and rapidly respond to environmental changes. We studied how the physical characteristics of the native habitat influence the spatial learning capacity of Anabas testudineus belonging to four different populations collected from two streams and two ponds, in a linear maze. Stream fish were able to learn the route faster than pond fish irrespective of the presence or absence of landmarks in the maze. However, climbing perch collected from ponds learned the route faster in the maze provided with landmarks than in Plain maze. The results indicate that fish inhabiting a lotic ecosystem use egocentric cues in route learning rather than visual cues like landmarks. A local landmark may be a more reliable cue in route learning in a relatively stable habitat like a pond. In flowing aquatic systems, water flow may continually disrupt the visual landscape and thus landmarks as visual cues become unreliable. Spatial learning is thus a fine-tuned response to the complexity of the habitat and early rearing conditions may influence the spatial learning ability in fish.     

Gill microcirculation of the air-breathing climbing perch, Anabas testudineus (Bloch):relationships with the accessory respiratory organs and systemic circulation

The general macrocirculation and branchial microcirculation of the air-breathing climbing perch, Anabas testudineus, was examined by light and scanning electron microscopy of vascular corrosion replicas. The ventral aorta arises from the heart as a short vessel that immediately bifurcates into a dorsal and a ventral branch. The ventral branch distributes blood to gill arches 1 and 2, the dorsal branch to arches 3 and 4. The vascular organization of arches 1 and 2 is similar to that described for aquatic breathing teleosts. The respiratory lamellae are well developed but lack a continuous inner marginal channel. The filaments contain an extensive nutritive and interlamellar network; the latter traverses the filament between, but in register with, the inner lamellar margins. Numerous small, tortuous vessels arise from the efferent filamental and branchial arteries and anastomose with each other to form the nutrient supply for the filament, adductor muscles, and arch supportive tissues. The efferent branchial arteries of arches 1 and 2 supply the accessory air-breathing organs. Arches 3 and 4 are modified to serve primarily as large-bore shunts between the dorsal branch of the ventral aorta and the dorsal aorta. In many filaments from arches 3 and 4, the respiratory lamellae are condensed and have only 1-3 large channels. In some instances in arch 4, shunt vessels arise from the afferent branchial artery and connect directly with the efferent filamental artery. The filamental nutrient and interlamellar systems are poorly developed or absent. The respiratory and systemic pathways in Anabas are arranged in parallel. Blood flows from the ventral branch of the ventral aorta, through gill arches 1 and 2, into the accessory respiratory organs, and then returns to the heart. Blood, after entering the dorsal branch of the ventral aorta, passes through gill arches 3 and 4 and proceeds to the systemic circulation. This arrangement optimizes oxygen delivery to the tissues and minimizes intravascular pressure in the branchial and air-breathing organs. The efficiency of this system is limited by the mixing of respiratory and systemic venous blood at the heart.     

Reproduction and spawning behavior of the climbing perch Anabas testudineus (Perciformes, Anabantidae) in an aquarium

Results of study of the spawning and reproductive behavior of the climbing perch Anabas testudineus in an aquarium are presented. Main specific features of reproduction of this species are revealed. In the performed experiments, climbing perches did not build a nest, did not prepare a spawning substrate, and did not show any forms of parental care. The pre-spawning and spawning behavior of the climbing perch is described, and fecundity and gonadosomatic index are determined. It is shown that intermittent spawning is typical of these fish. Mating system of the climbing perch is either polygamy or promiscuity. Sexual dimorphism in the climbing perch was not found. The eggs of the climbing perch have positive buoyancy and belong to the really pelagic type, which is rare for freshwater fish. Infanticide is a common phenomenon for the climbing perch. Breeding of the given species under aquarium conditions can be exercised without artificial hormonal stimulation, at different sex ratio, and under conditions of stocking density considerably exceeding standard aquacultural recommendations. The main specific features of reproduction of the climbing perch are discussed in relation to evolution of parental care in labyrinth fishes.     

Scanning electron microscopy of the post-embryonic stages of the climbing perch,Anabas testudineus

Different developmental stages, fertilized eggs through hatchlings, of the climbing perch,Anabas testudineus, have been studied by scanning electron microscopy. The surface specialization of eggs and hatchlings reveals that while the egg surface is reticulate in appearance, the hatchlings are covered with microridges. Vitelline arteries are seen at the pharyngeal and abdominal regions. They supply nutrients directly from the yolk sac to the developing embryo. Three pairs of such arteries are distinctly seen in the pharyngeal region. Mucous glands are discernible at places over the entire body surface of the embryo before the formation of scales. The skin seems to be helpful in gaseous exchange till the gills and accessory respiratory organs develop and become functional.     

Starvation induced cholesterogenesis in hepatic and extra hepatic tissues of climbing Perch,Anabas testudineus (Bloch)

Cholesterol is a structural lipid, which may be differentially utilized or synthesized in response to stress or during insulin deficient states such as starvation. In the present investigation we estimated the levels of cholesterol in Anabas testudineus, which was subjected to brief (15 days) and prolonged fasting (60 days). Tissues such as liver, kidney, brain, accessory respiratory organ, pectoral and lateral line muscle were selected for the study. Cholesterol content was estimated by the Crawford method (1958). Both the starvation regimes showed a significant increase in cholesterol levels in almost all the tissues, but for liver, which strangely showed an insignificant decline during the short-term starvation. This overall upsurge in cholesterol levels observed in all extra hepatic tissues may be attributed to the synthesis of stress hormones such as glucocorticoids, which may promote gluconeogenesis and adrenocorticoids, which may help the animal to combat the stressful condition of starvation. Anabas adapted well to starvation stress and survived all throughout the experimental period.     

Scanning electron microscopy of the respiratory organs of juvenile and adult climbing perch,Anabas testudineus

The gills and air-breathing organs of fingerlings (1–2.5 g) and adult (30 g)Anabas testudineus have been studied by scanning electron microscopy. The labyrinthine organs bear only one or two leaf-like plates in fingerlings of 1–2.5 g body weight. In very small finglerlings (1 g) no proper development of respiratory islets could be seen on the labyrinthine plates. There is evidence of the suprabranchial chambers being used for aquatic respiration in juvenile stages. In adults the inhalent and exhalent apertures become well defined with shutters developed on the first pair of gills, when they become obligatory air-breathers.     

Pituitary cytology of the freshwater teleost Anabas testudineus (Bloch)

In the pituitary of A. testudineus the rostral pars distalis (RPD), proximal pars distalis (PPD) and pars intermedia (PI) are arranged in a rostro-caudal axis. The rostral neurohypophysis (NH) extends dorsal to the pars distalis, while the caudal part vertically penetrates into the PI and ramifies in its component. The RPD mainly consists of erythrosinophils and PgH-positive cells which are comparable to the lactotropes and corticotropes mentioned in the literature. In the nonbreeding season, acidophils are the predominant cells of the PPD and are largely confined to its dorsal aspect. The two types of cyanophils present in the PPD could not be differentiated with the various techniques used in this study. However, those cyanophils which increase in number and are active during the spawning season may be the gonadotropes, while those which are cytologically inactive may be the thyrotropes. The pars intermedia consists of PAS+ and PhH+ cells. Trichrome and tetrachrome staining techniques revealed the presence of acidophils, cyanophils and amphiphils in the PI.     

Fine structure of the respiratory organs of the Climbing perch, Anabas testudineus (Pisces: Anabantidae)

An electron microscopic study has been made of the three respiratory organs of climbing perch. The gill structure is similar to that of the other telcosts but the thickness of the water/blood barrier is much greater, being as great as 20 μm in some specimens. The increased thickness is due to a multilayered epithelium which is thinner (3.5–7 μm) over the marginal channel of the secondary lamellae. The other two main layers, basement membrane and pillar cell flange, are relatively thin (about 1 μm).
The pillar cells have a typical structure, but in certain regions they are contiguous with one another and line well-defined blood channels. Some of the columns of basement membrane material in such regions may be common to adjacent pillar cells.
The air-breathing organs are (a) the lining of the suprabranchial chambers , and (b) the labyrinthine plates attached to the dorsal region of branchial arches. Electron microscopy showed that their structure is well adapted for gas exchange, the air/blood barriers being only 0.12–0.3 μm, comprising an epithelial layer, basement membrane, and thin capillary endothelium. The many parallel blood channels of the respiratory islets of both organs are separated by pillar-like structures which differ from the pillar cells of the secondary lamellae. Thus the hypothesis that the air-breathing organs represent modified gills is not supported by this study.
The fine structure of the non-respiratory region of the air-breathing organs is similar to that of the skin, and includes chemoreceptor-like cells. Evidence concerning the possible homology of pillar cells with plain muscle cells is discussed.     

The influence of hunger on food‐stocking behaviour of climbing perch Anabas testudineus

The present study demonstrated that the climbing perch Anabas testudineus collected and stocked food pellets in its mouth, a behaviour that has not yet been reported in any other species of fish. In this species, food deprivation for 24 h increased food stocking, but not food intake.     

Post-embryonic development of water- and airbreathing organs of Anabas testudineus (Bloch)

The development of respiratory surfaces in post-embryonic stages of Anabas testudineus was studied using morphometric methods on serial sections through the pharyngeal region of specimens obtained by induced breeding of known parentage. The larvae and fry were fixed in glutaraldehyde and osmium tetroxide. In the young stages aquatic respiration was found to be obligatory. The hatchlings come out of the egg membranes about 10 h after fertilization. During the yolk-sac stages gaseous exchange takes place through the well vascularized skin. The gills start differentiating at about 24 h and become functional at about 39 h. The labyrinthine organs begin to develop after 51 h but the hatchlings do not take an air breath until they reach 13–14 days. The appearance of scales at 11–14 days probably hinders cutaneous respiration and is correlated with the onset of aerial respiration.
Morphometric analysis using stereological methods shows high surface: volume ratios for the gills and labyrinthine organs as adaptations to gas exchange function. A marked decrease in surface: volume ratio for the suprabranchial cavities between 7 and 11 days indicates an increase in volume to accommodate the expanding labyrinthine plates which retain a fairly constant surface: volume ratio.     

Effect of gonadal steroids on respiratory metabolism of Anabas testudineus (Bloch)

The present investigation deals with the effect of gonadal steroids on the oxygen consumption (through gills only) in an air breathing fish, Anabas testudineus (Bloch). A good correlation (P less than 0.05) has been established between the seasonal variations in VO2 and cyclic changes in the activity of gonads in both the sexes. Oxygen consumption in both the sexes of A. testudineus were studied for a period of fourteen months. VO2 of male Anabas remained higher as compared to female throughout the period of investigation. Statistical as well as experimental analysis of the data also indicates that the "male hormones" are much more effective in bringing about the homeostasis of oxidative metabolism as compared to "female hormone" in this fish. The treatment with testosterone brings about significant (P less than 0.001) increase in VO2 in males though the lower dose proved to be most effective. Most of the "female hormones" (progesterone, Duogynon forte and Ovocyclin) used in the present investigation seem to decrease the VO2 significantly in females. The decrease in VO2 was more pronounced at higher dosage. Two peaks of VO2--first in June/July and second in October--have also been observed in this fish. The reason for and mechanism of such change are discussed in the present investigation.     

Thyroid hormones regulate lipid metabolism in a teleost Anabas testudineus (Bloch)

We compared the long-term action of 3,5,3′-triiodo-l-thyronine (T₃) and 3,5-diiodo-l-thyronine (T₂) on lipid metabolism in a teleost Anabas testudineus. Among the six groups of animals used in this experiment, except for the control group, all received 6-propylthiouracil (6-PTU) to create a hypothyroid state in order to analyse the action of iodothyronines on lipid metabolism. Injections of 6-PTU reduced T₃ concentration in the circulation by 79.6% and injections of iodothyronines enhanced the level of T₃ in the plasma, and a maximum increase was observed in T₃ (500 ng)-treated specimens. Analysis of lipogenic enzymes in liver and heart showed that a tissue-specific variation exists in the action of thyroid hormones and, in many cases, activity is higher in T₂-treated groups. Analysis of various lipid classes showed that long-term administration of T₂ is also effective in producing a comparable effect with that of T₃ on lipid metabolism.     

Oxygen uptake through water during early life of Anabas testudineus (Bloch)

The O₂ consumption (mg/hr) through water in case of Anabas testudineus during development and growth has been measured and its relationship to body weight or length studied.The logarithmic plot of 02 uptake through water either against body weight or length suggested a statistically significant (P > 3.53) two-component curve, the point of intersection being at 11 mg body weight and 1.78 cm body length. These are the theoretical values of weight or length at which the responsibility of supplementing nearly 40% of the total O₂ demand through the newly developed air breathing organ falls in the early life of the fish. One of the impelling causes forcing developing fry of Anabas to adopt a bimodal gas exchange machinery seems to be 4 fold increase in the diffusion distance at the gills.