Unusual hepatic mitochondrial arginase in an Indian air-breathing teleost,Heteropneustes fossilis: Purification and characterization

A functional urea cycle with both cytosolic (ARG I) and mitochondrial (ARG II) arginase activity is present in the liver of an ureogenic air-breathing teleost, Heteropneustes fossilis. Antibodies against mammalian ARG II showed no cross-reactivity with the H. fossilis ARG II. ARG II was purified to homogeneity from H. fossilis liver. Purified ARG II showed a native molecular mass of 96 kDa. SDS–PAGE showed a major band at 48 kDa. The native enzyme, therefore, appears to be a homodimer. The pI value of the enzyme was 7.5. The purified enzyme showed maximum activity at pH 10.5 and 55 °C. The K_m of purified ARG II for l-arginine was 5.25 ± 1.12 mM. l-Ornithine and N^ω-hydroxy-l-arginine showed mixed inhibition with K_i values 2.16 ± 0.08 and 0.02 ± 0.004 mM respectively. Mn^+ 2 and Co^+ 2 were effective activators of arginase activity. Antibody raised against purified H. fossilis ARG II did not cross-react with fish ARG I, and mammalian ARG I and ARG II. Western blot with the antibodies against purified H. fossilis hepatic ARG II showed cross reactivity with a 96 kDa band on native PAGE and a 48 kDa band on SDS–PAGE. The molecular, immunological and kinetic properties suggest uniqueness of the hepatic mitochondrial ARG II in H. fossilis.     

Surface ultrastructure of the olfactory rosette of an air-breathing catfish,Heteropneustes fossilis (Bloch)

The surface architecture of the olfactory rosette ofHeteropneustes fossilis (Bloch) has been studied by scanning electron microscopy. The olfactory rosette is an oval structure composed of a number of lamellae arranged pinnately on a median raphe. The raphe is invested with epithelial cells and pits which represent goblet cell openings. On the basis of cellular characteristics and their distribution the lateral surface of each olfactory lamella is identified as sensory, ciliated non-sensory and non-ciliated non-sensory epithelium. The sensory epithelium is provided with receptor and supporting cells. The ciliated non-sensory epithelium is covered with dense cilia obscuring the presence of other cell types. The non-ciliated non-sensory epithelium is with many polygonal areas containing cells.     

Studies on blood components of an air-breathing siluroid fish, Heteropneustes fossilis (Bloch) in relation to body weight.

Different haematological parameters have been studied in relation to the body weight of Heteropneustes fossil (Bloch). The erythrocytes and leucocytes number and haemoglobin concentration increases from lower to higher weight groups. The heart weight also increases along with other blood components. With the unit increase in the body weight of this fish, the heart weight, erythrocytes, leucocytes and haemoglobin increase by a fractional power of 0.85700, 0.13480, 0.13215 and 0.22876, respectively. This shows that haemoglobin increases at a higher rate than erythrocyte number. The coefficient of correlation between body weight and erythrocyte (r = 0.70015), leucocytes (r = 0.95861), haemoglobin (r = 0.96615) and heart weight (0.97577) indicate high degree of correlation. The erythrocytes and leucocytes count and haemoglobin concentration per gram body weight is higher in younger fishes and decrease as the animal grows in size. The haematocrit values and mean corpucsular volumes decrease from lower to higher weight groups, whereas mean corpuscular haemoglobin concentration increases with body weight. The erythrocyte cell surface has a decreasing trend from lower to higher weight group. Due to difference in the rate of decrease of greatest and least diameter of erythrocytes, the elliptical shape of R.B.C. which is common in younger animals, becomes circular in higher weight group. The non-granulocytes increase constantly while the percentage of granulocytes decreases from lower to higher weight groups. The lymphocytes constitute the main bulk of all the leucocytes. The total lymphocytes also increase with the body weight. Spindle cells and monocytes are relatively less in numbers. The percentage of eosinophils, basophils and neutrophils also decrease from lower to higher weight groups.     

Effect of ACTH and bilateral gonadectomy on the adrenocortical tissue of an air-breathing fish -- Heteropneustes fossilis (Bloch).

The mammalian ACTH (20 I.U.) injected in Heteropneustes fossilis (Bloch) caused hyperplasia of the adrenocortical tissue. The interrenal as well as chrome cells became vacuolated. The interrenal nuclear size increased by 15% as an average than the control fishes. The glycogen granules were found to be absent from the interrenal cells. The effect of bilateral gonadectomy in both sexes has been marked in the gradual decrease of the interrenal nuclear diameter which 12 weeks after the operation, recorded nearly 25% reduction in size. The glycogen content was reduced considerably. Removal of gonads during maturation period bringing inhibition of hyperplasia of the gland at the time of spawning possibly indicates action of gonadal steroids on the physiological alterations of the interrenal cells.     

Oxygen uptake through gills and skin in relation to body weight of an air-breathing siluroid fish, Saccobranchus (=Heteropneustes) fossilis

Oxygen uptake through gills and skin has been measured in juvenile and adult Saccobranchus fossilis and its relationship represented by the equation Vo₂= aW^b. When air-breathing is allowed the O₂ uptake via the gills and skin together increases by powers of 1 -084, 0–986 and 1–328 in juvenile, adult and juvenile+adult respectively. When air-breathing is prevented the slope (b) for O₂ uptake via the gills appear to be less in juveniles (0–765) than in adults (0–784) and juveniles+adults together (0–814). Under the same experimental condition, the slope for O₂ uptake via the gills+skin is also less in juveniles (0–478) than in adults (0–799) and juveniles+adults (0–755). Further decrease in the exponent value is found for the oxygen uptake of skin in relation to body weight under surfacing-prevented conditions ( b = 0–542). Different exponent values for juvenile and adult fishes may be due to their different growth pattern and physiology.     

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.     

Ureogenesis in a freshwater teleost: an unusual sub-cellular localization of ornithine-urea cycle enzymes in the freshwater air-breathing teleost Heteropneustes fossilis.

Sub-cellular localization of different ornithine-urea cycle enzymes was studied in the liver and kidney of a freshwater air-breathing teleost. Carbamyl phosphate synthetase, ornithine transcarbamylase, and arginase were found to be localized inside the mitochondria, and argininosuccinate synthetase and argininosuccinate lyase were found in the soluble fraction. Mitochondrial localization of arginase, a feature known in marine elasmobranchs and toadfishes, indicates the evolutionary position of H. fossilis to be different from that of present day freshwater teleosts.     

Seasonal changes in the hypothalamo-hypophyseal-ovarian system in the catfish,Heteropneustes fossilis (Bloch)*

The annual reproductive cycle of the catfish, H. fossilis (Bloch) is divided into the preparatory period (February-April), the prespawning period (May-June), the spawning period (July-August) and the postspawning period (September-January). During the early postspawning period (September-November), the hypothalamo-hypophyseal-ovarian system shows a gradual regression. In January, the hypothalamic nuclei, the pars magnocellularis (PMC), the pars parvocellularis (PPC) of the nucleus preopticus (NPO), and the nucleus lateralis tuberis (NLT) show renewed activity, as shown by a significant increase in their nuclear diameters and an accumulation of neurosecretory material (NSM) in their cell bodies. The hypophysis and the ovary remain quiescent. During the preparatory period, all the hypothalamic neurons studied indicate decreased activity but simultaneously show an accumulation of NSM in their cell bodies. The number of granulated basophils in the proximal pars distalis (PPD) of the hypophysis remains low but ovarian weights increase, presumably due to the multiplication of oogonia. In the prespawning period, there is a marked accumulation of NSM in the cell bodies of the hypothalamic neurons and at the same time the number of granulated basophils in the PPD of the hypophysis dramatically increases with concomitant increase in vitellogenic activity in the ovary. During the spawning period, the hypothalamic neurons continue to store NSM in their cell bodies and simultaneously there is a tremendous increase in the number of granulated basophils in the PPD of the hypophysis and the ovary has a large proportion of yolky primary oocytes. Spawning is associated with a significant degranulation of the granulated basophils in the PPD of the hypophysis. The significance of the results is discussed in relation to the environmental and hormonal regulation of seasonal ovarian activity.     

Edwardsiella tarda endotoxin as an immunopotentiator in Singhi,Heteropneustes fossilis fingerlings

Endotoxin of E. tarda grown in brain heart infusion broth at 30 degrees C for 18 hr was extracted by differential centrifugation. Fingerlings of H. fossilis (weighing 1-2 g) were allowed for hyperosmotic infiltration in the endotoxin at the rate of 0,2,4,8,16 and 20 mg/l. Mortality varied from 20-50% at 2 to 20 mg/ml. Toxin treated fishes were challenged 21 days post treatment with the same E. tarda strain containing 2.1 x 10(9) CFU/ml. There was 80% mortality in the control group whereas only 20% mortality in toxin treated group at 2 mg/l concentration after challenge with homologous E. tarda. Subsequently a second challenge of E. tarda was given to the survivors of fish one month after first challenge using same concentration where no mortality could be observed. It was concluded that the endotoxin could enhance percentage of survival against E. tarda infection in Singhi.     

Thyroid hormone-induced changes in different ion-specific adenosine triphosphatase activities in liver of Singi fish Heteropneustes fossilis (Bloch)

A single injection of different doses of T3 (0.5, 5, 20, and 50 micrograms/g) to Singi fish caused an increase in Na+K+-ATPase activity in crude liver homogenate in a dose-dependent non-linear fashion on the 3rd d. Ca++- and Mg++-ATPase activity increased only with 20 and 50 micrograms/g of T3. Lowering the dose of T3 to 0.1 microgram and 0.25 microgram/g in a single injection had not effect on these enzyme activities. TETRAC (1, 2, and 4 micrograms/g) and TRIAC (2 and 4 micrograms/g) in a single injection enhanced the activities of Na+K+-ATPase, but Ca++- and Mg++-ATPase activities remained unchanged on the 3rd d. Immersion of Singi fish in thiourea-containing medium (1 mg/ml) for 30 d caused reduction in Na+K+-ATPase activity, but Ca++- and Mg++-ATPase activity remained unaltered. The reduced level of Na+K+-ATPase activity in the thiourea-treated hypothyroid fish was recovered and even brought above the control level by a single injection of T3 at the dose of 0.5 microgram/g. Differential sensitivity of various ion-specific ATPases to T3 in liver of Singi fish is thus documented.     

Toxicity of mercury: A comparative study in air-breathing and non air-breathing fish

Annual primary production was estimated from two years data. The results indicate a high primary productivity and a short turn over time for nitrogen.

     

Landolt's club in the retina of catfish, Heteropneustes fossilis: a new finding in Teleostei

The visual cells in the retina of the freshwater catfish, Heteropneustes fossilis comprise rods, long single cones, short single cones and Landolt's clubs.