Jagdish Ojha

Vascular organization of the head and respiratory organs of the air-breathing catfish, Heteropneustes fossilis

Light and scanning electron microscopy of vascular replicas from the facultative air‐breathing fish Heteropneustes fossilis show modifications in the macrocirculation of the respiratory organs and systemic circulation, whereas, gill microcirculation is similar to that found in typical water‐breathing fish. Three and sometimes four ventral aortae arise directly from the bulbus. The most ventral vessel supplies the first pair of arches. Dorsal to this another aorta supplies the second gill arches, and a third, dorsal to, and larger than the other two, supplies the third and fourth arches and the air sacs. Occasionally a small vessel that may be the remnant of a primitive aortic arch arises from the first ventral aorta and proceeds directly to the mandibular region without perfusing gill tissue. The air sac is perfused by a large‐diameter extension of the afferent branchial artery of the fourth gill arch and its circulation is in parallel with the gill arches. Blood drains from the air sac into the fourth arch epibranchial artery. A number of arteries also provide direct communication between the efferent air sac artery and the dorsal aorta. All four gill arches are well developed and contain respiratory (lamellar) and nonrespiratory (interlamellar and nutrient) networks common to gills of water‐breathing fish. Air sac lamellae are reduced in size. The outer 30% of the air sac lamellar sinusoids are organized into thoroughfare channels; the remaining vasculature, normally embedded in the air sac parenchyma, is discontinuous. A gill‐type interlamellar vasculature is lacking in the air sac circulation. Despite the elaborate development of the ventral aortae, there is little other anatomical evidence to suggest that gill and air sac outflow are separated and that dorsal aortic oxygen tensions are maintained when the gills are in a hypoxic environment. Physiological adjustments to hypoxic water conditions probably include temporal regulation of gill and air sac perfusion to be effective, if indeed they are so.

Vasculature of the head and respiratory organs in an obligate air‐breathing fish, the swamp eel Monopterus (=Amphipnous) cuchia

Methyl methacrylate vascular corrosion replicas were used to examine the macrocirculation in the head region and the microcirculation of respiratory vessels in the air‐breathing swamp eel Monopterus cuchia. Fixed respiratory tissue was also examined by SEM to verify capillary orientation. The respiratory and systemic circulations are only partially separated, presumably resulting in supply of mixed oxygenated and venous blood to the tissues. A long ventral aorta gives rise directly to the coronary and hypobranchial arteries. Two large shunt vessels connect the ventral aorta to the dorsal aorta, whereas the remaining ventral aortic flow goes to the respiratory islets and gills. Only two pairs of vestigial gill arches remain, equivalent to the second and third arches, yet five pairs of aortic arches were identified. Most aortic arches supply the respiratory islets. Respiratory islet capillaries are tightly coiled spirals with only a fraction of their total length in contact with the respiratory epithelium. Valve‐like endothelial cells delimit the capillary spirals and are unlike endothelial cells in other vertebrates. The gills are highly modified in that the lamellae are reduced to a single‐channel capillary with a characteristic three‐dimensional zig‐zag pathway. There are no arterio‐arterial lamellar shunts, although the afferent branchial artery supplying the gill arches also supplies respiratory islets distally. A modified interlamellar filamental vasculature is present in gill tissue but absent or greatly reduced in the respiratory islets. The macro‐ and micro‐circulatory systems of M. cuchia have been considerably modified presumably to accommodate aerial respiration. Some of these modifications involve retention of primitive vessel types, whereas others, especially in the microcirculation, incorporate new architectural designs some of whose functions are not readily apparent.

Interspecific variations in the surface ultrastructure of the gills of freshwater mullets.

SEM studies were made on the gills of freshwater mullets,Rhinomugil corsula andSicamugil cascasia, to correlate surface ultrastructure of various gill units with their probable functions. Two types of lamellated gill rakers of the former fish are suited for plankton feeding and the short, stumpy and transversely beaded gill rakers of the latter reflect the varied food and feeding habit of the fish.R. corsula has numerous mucous glands on the epithelium covering the gill arch and gill filaments,S. cascasia has fewer. In accordance with the differences in the density and distribution of the mucous glands, the microridged epithelial cells also show variations in their architectural plan. In both species the epithelium of the secondary lamellae is smooth, probably an adaptation for better gaseous exchange.

Scanning electron microscopy of the gills of a freshwater catfish,Rita Rita

Variations in the gross morphology and surface architecture of the gill filaments and secondary lamellae of a freshwater catfish (Rita rita) have been investigated using scanning electron microscopy. Heterogeneity of the gill has been correlated with the distribution of lamellar water-flow at different regions of a gill filament. Higher lamellar water flow (cc/pore/cmH2O/sec) was estimated for the middle region of the filaments. The filaments are covered with epithelial cells whose surface is provided with well-developed microridges. The lamellae are generally covered with microvillous epithelial cells. The variations in surface architecture of the gill filaments and secondary lamellae have been correlated with their probable functions.

Bimodal oxygen uptake in juveniles and adults amphibious fish, Channa (= Ophiocephalus) marulius

Oxygen uptake of Channa marulius was studied under water with and without access to air. There was a significant increase in the oxygen uptake through the gills when access to air was prevented. However, this value (0.863 ± 0.058 mlO2/indiv./h) was quite low in comparison to the total bimodal oxygen uptake (2.04 ± 0.14 mlO2/indiv./h) in juveniles. In adult fish the oxygen uptake per unit time increased appreciably (4.673 ± 0.404 mlO2/indiv./h). In juveniles as well as in adults the air breathing dominated over aquatic breathing. This fish showed a definite circadian rhythm in the bimodal oxygen uptake during different hours of the day.

Effect of branchial parasites on the efficiency of the gills of a freshwater catfish, Wallago attu

For the first time, an attempt has been made to quantify the effect of a copepod parasite (Ergasilus bengalensis) on the respiratory efficiency of the gills of a riverine catfish (Wallago attu) using an important parameter – the diffusing capacity. In addition, scanning electron microscopy has been used to demonstrate the effect of a monogeneid fluke on the gill lamellae of this catfish. The anchorage of E. bengalensis towards the leading edge of the interlamellar channels (pores) will affect laminar flow of water through the gill sieve. About 35% of the water flow (1.23×10−3 cm3/s) and lamellar area (15.41 mm2) of an infected gill filament (4.46 mm) is affected by the copepod parasite (1.59 mm). Other effects of the monogeneid flukes on the catfish included fusion of the tips of gill filaments and distortion of lamellar epithelium. Parasite-induced changes in the branchial organization are discussed in relation to oxygen uptake efficiency of the gills of the catfish.

Morphometrics, micromorphology, microanatomy and cytochemistry of the gills of a swamp catfish, Chaca chaca (Ham.)

Dimensions, micromorphology, microanatomy and cytochemistry of the gills of a swamp catfish,Chaca chaca have been investigated using morphometric, scanning electron microscopic, light microscopic and cytochemical techniques respectively. The findings have been correlated with the respiratory efficacy of the gill sieve and the physicochemical behaviour of the habitat of the fish.The filament number among 4 gill arches varies from 144–151 and does not show any significant (P>0·05) difference among themselves. The filament length shows heterogeneity in their relative dimensions at different points along the various hemibranchs of the 4 gills. Lamellar frequency (n) and area (bl) were 31·2 and 0·08316 mm2 respectively. The small gill area (13905·3 mm2) assigns comparatively low level of activity to the catfish. Total lamellar water flow of the gill sieve ofChaca was 20·123 cc/s.The heterogenous gill arch epithelium contained taste buds and mucous gland openings. Short and stumpy gill rakers signify carnivorous feeding habit of the catfish. The micropockets of the gill filament epithelium entrap some water molecules to protect the gills from desiccation, when the fish is temporarily exposed to water-land interface and acts as a regular source of oxygen to the fish during adverse ecological conditions.

Effect of body size on the dimensions of the respiratory organs of a freshwater catfish,Mystus vittatus

The data on gill and skin dimensions of 12 freshwater catfishMystus vittatus ranging from 3 g to 23 g in relation to body weight have been analysed using logarithmic transformation. The exponent value for total gill area was 0.789; corresponding values for 1st, 2nd, 3rd and 4th gill arches and skin were 0.753, 0.772, 0.816, 0.823 and 0.631 respectively. The gill diffusing capacity (0.211) was greater than that for skin (0.002).