Fourth Gill Arches Research Articles

Some morphological structures and histological features of the gills of Binni (Mesopotamichthys sharpeyi)

This study aimed to describe some morphological and histological aspects of the binni fish's gills. Fifteen adult male binni were pulled alive from the Al-Forat River at about (24 - 28) months, immediately after death. The gills of binni were situated on each side of the head beneath a gill cover; the operculum and the gills were made of finger-like long filaments joined to the cartilaginous gill bar. From each filament, numerous fragile lamellae that resemble leaves protrude. These lamellae comprised tiny capillaries covered in plain squamous epithelial cells. The epithelium acts as a barrier between the fish's blood and the surrounding water. The first, second, third, and fourth pairs of gill arches make up the gills supported by the bone skeleton. Each arch carries a row of gill filaments on its convex side and two rows of gill rakers on its concave side. On the rostral concave border, the filaments in the two extremes of the gill were short, but the length of all the filaments was the same. The first-gill arch's lateral rakers were longer than the medial rakers, while the fourth gill arch's medial rakers were longer than the lateral rakers. The rakers, bony comb-like projections, filled the rostral region of the gill arches at the rostral concave interior side. There was interdigitation between the gill rakers of the neighboring gill arches. Each gill arch included the lateral gill rakers pointing dorsolaterally and medial gill rakers pointing dorsomedially. Filaments originate from the gill arches and are maintained by the cartilage on the caudal convex border of the primary lamellae, from which the secondary lamellae emerge. The simple squamous epithelium lined the secondary lamellae. Keywords: Binni, Gill, Morphology, Histology

Do air-breathing fish suffer branchial oxygen loss in hypoxic water?

In hypoxia, air-breathing fish obtain O2 from the air but continue to excrete CO2 into the water. Consequently, it is believed that some O2 obtained by air-breathing is lost at the gills in hypoxic water. Pangasionodon hypophthalmus is an air-breathing catfish with very large gills from the Mekong River basin where it is cultured in hypoxic ponds. To understand how P. hypophthalmus can maintain high growth in hypoxia with the presumed O2 loss, we quantified respiratory gas exchange in air and water. In severe hypoxia (PO2: ≈ 1.5 mmHg), it lost a mere 4.9% of its aerial O2 uptake, while maintaining aquatic CO2 excretion at 91% of the total. Further, even small elevations in water PO2 rapidly reduced this minor loss. Charting the cardiovascular bauplan across the branchial basket showed four ventral aortas leaving the bulbus arteriosus, with the first and second gill arches draining into the dorsal aorta while the third and fourth gill arches drain into the coeliacomesenteric artery supplying the gut and the highly trabeculated respiratory swim-bladder. Substantial flow changes across these two arterial systems from normoxic to hypoxic water were not found. We conclude that the proposed branchial oxygen loss in air-breathing fish is likely only a minor inefficiency.

Micro-morphological characteristics of the oropharyngeal cavity floor of bogue (Boops boops) (Linnaeus, 1758) fish: gross morphology, light, and scanning electron microscopic imaging

The current study is the first to use gross anatomy, light, and scanning electron microscopy to describe the oropharyngeal cavity of a bogue (Boops boops Linnaeus, 1758) fish. Fourteen 17–18 cm long bogue fish were used. The lower jaw held the lower lip, labial teeth, tongue, and pharyngeal teeth, and the oral cavity floor appeared u-shaped. The lower jaw was small and narrow in the anterior and wide in the posterior as it approached the esophagus. The lower lip carried different lengths of cilia-like projections that looked like the cactus plant arranged in transverse layers, and its apex appeared as an open rose. These cilia were encircled by ridges that looked like sea waves. The labial teeth were 15 in a row, with long roots placed beneath a pocket-like structure. Long, medium, and short pharyngeal papilliform teeth emerged on the oropharyngeal cavity floor at the level of the fourth gill arch in a small V-shaped arrangement. The tongue was smooth and small, with an apex, body, root, and lateral edges that were all clearly defined. The tongue’s apex was pointed and triangular, with a thin, transparent apical pouch around it. There was a median longitudinal fold on the dorsum of the tongue body and root. On the tongue surface, taste bud types I and II emerged. The bogue fish’s oropharyngeal cavity had unique anatomical characteristics, indicating that it was omnivorous.

Morphological investigation of the gills of the dusky grouper Epinephelus marginatus (Lowe 1834) using gross anatomy and scanning electron microscopy.

The current study has designed to investigate the morphological characteristics of the gills of the dusky grouper (Epinephelus marginatus) by gross morphology, scanning electron microscopy, and morphometric analysis. The study was carried out on 10 fresh fish. The fish has four-gill arches on each side. The lengths of the first-, second-, third-, and fourth-gill arches were 5.27, 4.2, 3.2, and 2.8cm. The gill arches carried a longitudinal band, the bases of the gill filaments, and gill rakers that varied from rectangular to circular shapes. Each gill arch had two main lateral and medial rows and two accessory rows of gill rakers in an alternative manner with each other. The dusky grouper fish had long rakers, whereas the longest one was the lateral rakers of the first arch, which were 467 and 1271.9μm in width and length. Three types of spines appeared on the gill arches and rakers. The long spine had detected on the apex of the short rakers. Each gill arch carried on its ventral side two rows of gill filaments. The long filaments were at the middle of the gill arch, while the short ones were at the rostral end of the gill arch. The study has demonstrated the taste buds, mucous, chloride cells, and significant features of the epithelial covering of the gill arches and rakers. The morphology of the gills of the dusky grouper indicates the adaptation to their marine environment.

Gill morphology of Bagrus bayad (Forskal, 1775) using scanning electron microscopy.

The work under investigation is carried out to describe the gross morphology and ultrastructure of the gills of the species Bagrus bayad grossly and with the help of scanning electron microscopy. The current work carried on ten fresh adult Bagrus bayad. Bagrus bayad is a genus of the Bagridae family. Our results revealed that the operculum opened caudoventrally. The wide interbranchial septum consisted of four transverse raised areas on each side that connected by transverse lines caudal to the base of the tongue. The gill arch is divided into long ceratobranchial and the short epibranchial clearly and formed an angle between them in the first three gill arches but in the fourth-gill arch is not clear. The first two gill arches have only lateral rackers. The first arch carried well-developed long rackers while rackers on the following rows were short. The majority of gill rackers were short as an adaptation of the carnivorous feeding habit of the Bagrus bayad. The gill arch and rackers were covered by pavement cells with chloride and mucus cells. The pavement cell surface has numerous microridges giving them the fingerprint's appearance. The gill filament's length is nearly fixed along the entire gill arch. Along the gill arch, and the gill filament carried leaf-like gill lamellae. At higher magnification, the gill filament appeared covered by irregular polygonal cells that have concentric microridges.

Morphology of the feeding apparatus in the herbivorous mudskipper, Boleophthalmus pectinirostris (Linnaeus, 1758)

Gaining the ability to feed in terrestrial environment allows fish to exploit novel food resources. However, the difference in physical characteristics between air and water, i.e., much lower density and viscosity of the former, would dictate a change in feeding mechanisms: suction feeding, the dominant feeding mode of aquatic vertebrates, hardly works in the air. There are some extant amphibious fishes that feed on land. However, most published studies have dealt with the feeding mechanisms of carnivorous amphibious fishes that prey on relatively large food items, and little is known about herbivorous fishes grazing on land. In this study, we investigated the morphology of the feeding apparatus of Boleophthalmus pectinirostris, a herbivorous mudskipper, to understand how feeding apparatus is modified for grazing on land. Dentition, and the skeletal and muscular systems of the branchial basket were examined through macroscopic and microscopic dissection, scanning electron microscopy, and micro-computed topography scanning. The results show that the feeding apparatus of the fish has been modified presumably to transport diatom cells from the mudflat surface to the digestive tract with minimum admixture of mud particles. The modifications include horizontal orientation of the lower jaw teeth, horizontally aligned, high-density gill rakers on the third (only on the posterior raw) and fourth (both rows) gill arches, large pharyngeal plates bearing numerous fine teeth, and the musculoskeletal system of the branchial basket.

A new species of sardine, Sardinella electra (Teleostei: Clupeiformes: Clupeidae), from the Ryukyu Islands, Japan.

A new species of sardine, Sardinella electra, is described on the basis of 18 specimens collected from the Ryukyu Islands, Japan. The new species closely resembles Sardinella hualiensis (Chu Tsai 1958) in that both species have a caudal fin with black tips, a black spot on the dorsal-fin origin, and both have lateral scales with centrally continuous or overlapping longitudinal striae. However, the new species is distinguished from S. hualiensis by its higher total gill-raker counts on the first, second, third and fourth gill arches, and on the posterior face of the third gill arch (105-121, 107-120, 88-104, 65-82, and 25-31, respectively, vs. 87-107, 83-105, 67-90, 53-69, and 13-27), and in having scales with few perforations and lacking pores posteriorly (vs. scales with numerous perforations and pores on their posterior margins).

Stolephorus continentalis, a new anchovy from the northwestern South China Sea, and redescription of Stolephorus chinensis (Günther 1880) (Clupeiformes: Engraulidae)

Stolephorus continentalis sp. nov. is described from 36 specimens from Hong Kong and northern Vietnam. The new species is closely related to the endemic Chinese anchovy S. chinensis (Gunther 1880), which is redescribed with a lectotype designated, with both species having a long upper jaw with the posterior tip just reaching to the posterior border of the preopercle; no predorsal scute; the posterior preopercular border rounded, convex; the posterior tip of the depressed pelvic fin not reaching to vertical through dorsal-fin origin; a pair of dark patches behind the occiput without a following pair of dark lines; and no black spots below the eye and lower-jaw tip. However, the new species is distinguished from S. chinensis in having higher total gill-raker counts on the first, second, third, and fourth gill arches (43–48, 33–40, 23–26, and 18–21, respectively vs. 35–41, 29–34, 19–24, and 16–19), and longer pectoral (16.5–19.2 % SL vs. 15.8–16.4 %) and pelvic fins (9.1–11.6 % SL vs. 8.2–8.3 %). Examination of the specimens previously considered as S. chinensis from Southeast Asia revealed that they differed from true S. chinensis and S. continentalis in having eight transverse scales (vs. 10 in the latter two species). The applicable scientific name for the Southeast Asian species is suggested here as Stolephorus oceanicus Hardenberg 1933.

A new species of the deepwater scorpionfish genus Phenacoscorpius (Teleostei: Scorpaenidae) from the Galápagos Islands

A new species of scorpionfish, Phenacoscorpius mccoskeri, is described based on three specimens from the Galápagos Islands, Ecuador, eastern Pacific. The new species is distinguished from other species of Phenacoscorpius by the following combination of characters: 19–20 pectoral-fin rays, middle rays branched; 5–19 pored lateral-line scales; palatine teeth present; small slit behind fourth gill arch; second preopercular spine absent; and nuchal and parietal spines distinct; in addition to some morphometric characters, including head length and width, interorbital width, caudal-peduncle depth and postorbital length.

A new species of anchovy, Encrasicholina auster (Clupeiformes: Engraulidae) from Fiji, southwestern Pacific Ocean

ABSTRACTEncrasicholina auster sp. nov. (Clupeiformes: Engraulidae) is described on the basis of six specimens collected from Fiji, southwestern Pacific Ocean. The new species is distinguished from congeners by the following combination of characters: long upper jaw (posterior tip extending beyond posterior margin of preopercle) 20.8%–22.5% standard length (SL); long lower jaw 19.0%–20.7% SL; long head 29.1%–29.2% SL; three unbranched rays in the dorsal and anal fins; transverse scales 11; branched pectoral-fin rays 12–13; pseudobranchial filaments 19–21; gill rakers 45–49, 40–43, 26–31 and 22–25 on the first, second, third and fourth gill arches, respectively.

Application of compound mixture of caprylic acid, iron and mannan oligosaccharide against Sparicotyle chrysophrii (Monogenea: Polyopisthocotylea) in gilthead sea bream, Sparus aurata.

We have evaluated the therapeutic effect of a compound mixture of caprylic acid (200 mg/kg fish), organic iron (0.2% of diet) and mannan oligosaccharide (0.4% of diet) in gilthead sea bream, Sparus aurata Linnaeus, infected with Sparicotyle chrysophrii Beneden et Hesse, 1863 in controlled conditions. One hundred and ten reared and S. chrysophrii-free fish (197 g) located in a cement tank were infected by the parasite two weeks following the addition of 150 S. chrysophrii-infected fish (70 g). Growth parameters and gill parasitic load were measured in treated against control fish after a ten-week-period. Differences in final weight, feed conversion ratio, specific growth rate and feed efficiency were not statistically significant between the experimental groups, suggesting no evident effect with respect to fish growth during the study period. Although the prevalence of S. chrysophrii was not affected by the mixture at the end of the experiment, the number of adults and larvae was significantly lower. The mean intensity encompassing the number of adults and larvae was 8.1 in treated vs 17.7 in control fish. Individual comparisons of gill arches showed that the preferred parasitism site for S. chrysophrii it the outermost or fourth gill arch, consistently apparent in fish fed the modified diet and in control fish. In conclusion, the combined application of caprylic acid, organic iron and mannan oligosaccharide can significantly affect the evolution of infection with S. chrysophrii in gilthead sea bream, being capable of reducing adult and larval stages of the monogenean. However, no difference in growth improvement was observed after the trial period, potentially leaving space for further optimisation of the added dietary compounds.

Distribution of Cardicola forsteri eggs in the gills of southern bluefin tuna (Thunnus maccoyii) (Castelnau, 1872)

The distribution of Cardicola forsteri eggs in the gills of southern bluefin tuna (Thunnus maccoyii) was analysed. Eggs were confirmed to be C. forsteri using laser-capture microdissection and quantitative polymerase chain reaction (qPCR) analyses. Prevalence of infection was significantly higher in the second gill arch (χ2=6.49, P<0.05) than in the fourth gill arch, and significantly lower in the basal region of the second gill arch (χ2=6.29, d.f.=2, P<0.05). The intensity of infection was not significantly different between the gill arches (F=0.03, d.f.=1, P>0.05). Similarly, there was no significant difference in the intensity of C. forsteri eggs between the gill arches (F=3.43, d.f.=2, P>0.05), or at different depth of sectioning (F=0.08, d.f.=1.12, P>0.05). Results suggest that the presence of C. forsteri eggs in the gills of tuna is more likely to be detected by sampling the second gill arch. Furthermore, targeting the middle region and increasing the sectioning depth may reduce the proportion of false negatives.

Cardiorespiratory responses to hypoxia in the African catfish, Clarias gariepinus (Burchell 1822), an air-breathing fish

The African catfish, Clarias gariepinus, possesses a pair of suprabranchial chambers located in the dorsal-posterior part of the branchial cavity having extensions from the upper parts of the second and fourth gill arches, forming the arborescent organs. This structure is an air-breathing organ (ABO) and allows aerial breathing (AB). We evaluated its cardiorespiratory responses to aquatic hypoxia. To determine the mode of air-breathing (obligate or accessory), fish had the respiratory frequency (f (R)) monitored and were subjected to normoxic water (PwO(2)=140mmHg) without becoming hyperactive for 30h. During this period, all fish survived without displaying evidences of hyperactivity and maintained unchanged f (R), confirming that this species is a facultative air-breather. Its aquatic O(2) uptake ([Formula: see text]) was maintained constant down to a critical PO(2) (PcO(2)) of 60mmHg, below which [Formula: see text] declined linearly with further reductions of inspired O(2) tension (PiO(2)). Just above the PcO(2) the ventilatory tidal volume (V (T)) increased significantly along with gill ventilation ([Formula: see text]), while f (R) changed little. Consequently, the water convection requirement [Formula: see text] increased steeply. This threshold applied to a cardiac response that included reflex bradycardia. AB was initiated at PiO(2)=140mmHg (normoxia) and air-breathing episodes increased linearly with more severe hypoxia, being significantly higher at PiO(2) tensions below the PcO(2). Air-breathing episodes were accompanied by bradycardia pre air-breath, to tachycardia post air-breath.

Morphological and Biochemical Variations in the Gills of 12 Aquatic Air-Breathing Anabantoid Fish

All fish species in the Anabantoidei suborder are aquatic air-breathing fish. These species have an accessory air-breathing organ, called the labyrinth organ, in the branchial cavity and can engulf air at the surface of the water to assist in gas exchange. It is therefore necessary to examine the extent of gill modification among anabantoid fish species and the potential trade-offs in their function. The experimental hypothesis that we aimed to test is whether anabantoid fishes have both morphological and functional variations in the gills among different species. We examined the gills of 12 species from three families and nine genera of Anabantoidei. Though the sizes of the fourth gill arch in three species of Trichogaster were reduced significantly, not all anabantoid species had morphological and functional variations in the gills. In these three species, the specific enzyme activity and relative protein abundance of Na(+)/K(+)-ATPase were significantly higher in the anterior gills as compared with the posterior gills and the labyrinth organ. The relative abundance of cytosolic carbonic anhydrase, an indicator of gas exchange, was found to be highest in the labyrinth organ. The phylogenetic distribution of the fourth gill's morphological differentiation suggests that these variations are lineage specific, which may imply a phylogenetic influence on gill morphology in anabantoid species.

Microhabitat distribution of some monogenoideans, parasitizing the gills of Wallago attu (Bl. and Sch., 1801) and their seasonal variation

The parasitic microhabitat distribution of the monogenoideans Thaparocleidus wallagonoius Jain, 1952, Mizelleus indicus Jain, 1957and T. gomtius Jain, 1957 parasitizing the gills of a fresh-water demersal Wallago attu and their seasonal variations were investigated in the present study. The microhabitat preferences of these species were observed. The gill segments and gill areas were the most important factors segregating the monogenoidean parasites on gills, not their abundance. Low niche overlap was found within each of the four gill arches and parasites were segregated in the same microhabitats within each gill arch. The distribution of parasites was independent of the left or right side of gill. The distribution plots in our study indicated that the anterior segment of first and fourth gill arches were more preferred site of infection. Seasonal variation of parasites, recorded during 2006 & 2007, in male and female hosts was also investigated. Due to ectoparasitic nature and high host specificity exhibited by the species of monogenoidea, studies on their seasonal dynamics are very significant as they could contribute significantly to the understanding of their biological adaptations to their environment.

Anatomical, Light and Scanning Electron Microscopic Studies on the Air Breathing Dendretic Organ of the Sharp Tooth Catfish (Clarias gariepinus)

Previously, it has been shown that different species of fishes are adapted in varying degrees for gaseous exchange in both water and air. Our study was carried out on sharp tooth catfish (Clarias gariepinus) obtained from the Nile River, Egypt and focused on the dendretic organ (DO) investigating its anatomical, scanning and light microscopical features. Anatomically, the air-breathing dendretic organ of the catfish was located in the suprabranchial chamber caudodorsal to the gills and composed of two main parts; small and large ones originated by main stems from the second and fourth gill arches respectively. Histologically, the DO either in its main stems or in the smaller branches and in the end bulbs consists of core of elastic cartilage, vascular layer of connective tissue and covering epithelium containing intraepithelial mucous glands. The blood capillaries (channels) were found to originate from the vascular layer and penetrate the covering epithelium. Toward the surface, these capillaries dilate and bulge out due to engorgement with RBCs forming what is called respiratory papillae. The SEM showed that the stem divisions and their bulbus ends contained double parallel rows of paired projections (respiratory lamellae) separated by areas of smooth surface. Moreover, the surfaces were studded with microvilli. In conclusion, the structure of this organ manifests profuse internal subdivision that may produce a particularly large respiratory surface area to extract the oxygen from air. Therefore, the catfish might be one of the most suitable fish for the intensive production in the fish aquaculture.

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.

SPATIAL DISTRIBUTIONS OF TWO SPECIES OF MONOGENEANS ON THE GILLS OF SIGANUS FUSCESCENS (HOUTTUYN) AND THEIR SEASONAL DYNAMICS IN CAGED VERSUS WILD-CAUGHT HOSTS

Two monogeneans species, Polylabris mamaevi Ogawa & Egusa, 1980 and Tetrancistrum nebulosi Young, 1967, are sympatric on the gills of Siganus fuscescens (Houttugn, 1782) in the South China Sea. An investigation into their distribution on the host's gills based on monthly samples from both wild and caged populations revealed that these 2 species co-occurred on the same gill arches, but they were segregated. P. mamaevi attached to the distal half of the gill filaments, whereas T. nebulosi attached to the proximal half. This difference may partly be attributed to microhabitat specialization. Microhabitat distributions were intensity dependent for both species. As intensity increased, monogeneans were increasingly found on the second, third, and even fourth gill arches, and niche breadths increased. The changes in distribution and niche breadths at the host gill arch level in relation to differences in host size and sampling period were considered to represent a functional response to increased intensity. Differences in host resources, in either net-caged or wild populations, did not significantly influence the parasite distributions at the host gill arch level. Simultaneous infections of these 2 species were common, but there was no evidence of negative interspecific interactions.

Gill area and dimensions of gilthead sea bream Sparus aurata L.

Detailed measurements of gill area and constituent variables (total filament length, lamellar frequency and bilateral area) were performed on both hemibranchs of all eight arches in six specimens of gilthead sea bream Sparus aurata (mean ±s.e. 49·9 ± 0·2 g). Shrinkage was also quantified and results were corrected accordingly. Filament number decreased from the first to the fourth gill arch, and average bilateral area of secondary lamellae was higher in the second and third arches. Total and mean filament length, total number of secondary lamellae and total gill area (ATG) were lower in posterior than in anterior hemibranchs of the second, third and fourth gill arches; while the opposite was observed for the first arch. Lamellar frequency was increased in posterior hemibranchs of all arches compared to that in anterior hemibranchs, especially at the fourth arch. Comparison of the actually measured ATG and constituent variables with estimates revealed that the third gill arch is the most representative for appropriate measurements and that any of its components (even one hemibranch) approximates the best ATG (within the range of 0·2–4·3%, P &gt; 0·05) and related dimensions. Consequently, necessary measurements were restricted to the posterior hemibranch of the third gill arch, and ATG and dimensions (y) were estimated in 21 specimens (23·5–217·6 g) and correlated to body mass (M) according to the allometric equation y = aMb. As fish increased in size, ATG (b= 0·664), total (b= 0·425) and mean (b= 0·323) filament length, total number of filaments (b= 0·103) and secondary lamellae (b= 0·377), as well as average lamellar bilateral area (b= 0·288), increased, while the opposite was observed for lamellar frequency (b=−0·049) and mass‐specific area (b=−0·336). Data obtained are discussed in relation to S. aurata activity and living ethology.

Morphological study on the gills of two species of fresh water fishes: Oreochromis niloticus and Clarias gariepinus

The gross and microscopic morphology of the gills of both Nile tilabia (Oreochromis niloticus) and sharptooth catfish (Clarias gariepinus) were described including light and scanning electron microscopy. The anatomical differences between the gill system of the two species were basically related to the geometry of the head and opercular cavities. Each species had four pairs of gills which were connected in a median interbranchial septum. In addition, a fifth rudimentary gill without gill filaments was found in catfish. The lengths and gaps between the gill arches in both species decreased medialwards. The gill rakers of tilabia were generally short and widely spaced compared to the long and narrow spaced rakers of the catfish. The gill filaments and lamellae of tilabia were longer than those of the catfish indicating a greater gill surface area in the former species. The catfish was additionally supplied by modified gills in the form of branched bulbous dendritic structures originating from the second and fourth gill arches. Scanning electron microscopy revealed that the surface of both gill filaments and lamellae was covered by polyhedral cells in tilabia and oval or elongated cells in catfish. These cells carried numerous microplicae which were better developed in tilabia. All gill parts, as revealed by light microscope, were nearly covered by mucous epithelium, however, the mucous cells were present on the lamellae of the catfish only. The rakers of both species demonstrated many taste buds and infiltrating lymphocytes in the epithelial covering. In catfish, in particular, several alarm substance cells were also scattered in this epithelium.