Journal of Agricultural Sciences
Vol. 58, No. 2, 2013
Pages 139-146
DOI: 10.2298/JAS1302139I
UDC: 597.551.4:591.123(669)
Original scientific paper
HISTOLOGICAL OBSERVATIONS ON THE DENDRETIC ORGAN OF
THE FARMED ADULT AFRICAN CATFISH (CLARIAS GARIEPINUS)
FROM EASTERN NIGERIA
Ekele Ikpegbu*, Uchenna Nlebedum, Okechukwu Nnadozie and
Okezie Agbakwuru
Department of Veterinary Anatomy, Michael Okpara University of Agriculture
Umudike, Abia State, Nigeria
Abstract: The histology of the accessory respiratory organ of the African
catfish – dendretic organ was investigated to reveal its microanatomy. The data
obtained will provide baseline data for further investigative research and assist fish
pathologists. The histology showed that the tubular shaped dendretic organ was
covered by stratified squamous epithelium containing periodic acid-Schiff (PAS)
and alcian blue (AB) positive mucous cells. On most surfaces, the epithelial cells
were organized into columns with mucous cells placed in-between the epithelial
cell columns. At the tip of the surface, capillaries were lined by endothelium at the
surface epithelium/air contact area. The subepithelial layer was of loose connective
tissue containing adipose tissue and occasional blood vessels. The core of the
dendretic organ contained elastic cartilage surrounded by a dense layer of
perichondrium. Elastic fibres were observed the territorial and inter-territorial
spaces.
Key words: mucous cells, histochemistry, surface capillaries, epithelium.
Introduction
The gill is the main organ for gas exchange in fish (Ahmed et al., 2008). This
mechanism is achieved through the exchange of gasses between dissolved air in
water and the vascular mesh of the gills. In the Indian subcontinent, fish species
with highly vascularised skin has been associated with the exploitation of dissolved
air in water (Devi and Banerjee, 2007). In some Teleosts, the amphibious fish,
some organs have become modified for atmospheric gas exchange. These organs
are referred to as air breathing organs (ABOs) (Devi and Banerjee, 2007). ABOs
are also referred to as accessory respiratory organs and they include: the modified
gill structures of the suprabranchial chamber of the Channa striata, dendretic organ
of sharptooth catfish from the Nile River, skin of Alticus kirkii and Periophthalmus
*
Corresponding author: e-mail: [email protected]
140
Ekele Ikpegbu et al.
magnuspinnatus, plicated labyrinthine organs of Anabas testudineus, swim bladder
in Bowfin Amia calva, the rich vascularized lips of Piaractus nigripinnis, and
intestinal air breathing of loach Lepidocephalichthys guntea (Bransons and Hake,
1972; Munshi et al., 1986; Moitra et al., 1989; Gervais and Tufts, 1998; Park,
2002; Ahmed et al., 2008; Ahmed and Mekkawy, 2011).
The development of these ABOs has been associated with the amphibious
feature of utilizing both aquatic and terrestrial habitat (Gordon et al., 1969).
Generally, amphibious behavior is related with a reduction in water quality or
quantity and/or biotic factors like fights, cannibalism and predation (Sayer and
Davenport, 1991; Martin, 1995; Taylor, 2000). Hence, within the science of
vertebrate evolution, amphibious fishes represent one of the intermediate stages
between the aquatic life and terrestrial habitation (Sayer, 2005).
Owing to the importance of respiration for tissue metabolic activities (Maina,
2002), a number of studies are published in order to describe morphology of
ABOs. These include using them as bio-markers for heavy metal contamination in
waters, provision of normal histomorphology to aid investigative researches
(Munshi et al., 1986; Banerjee and Chandra, 2005; Devi and Banerjee, 2007).
Despite the increasing importance of African catfish as a cultivable species of
choice in most commercial aquaculture in Nigeria, there is a dearth of information
from available literature on the microanatomy of this ABO – the dendretic organ.
The data obtained from fish from a commercial farm will provide baseline data for
further investigative research and aid clinicians in disease diagnosis.
Material and Methods
Seven adult African catfish from a commercial aquaculture farm with concrete
tanks in Eastern Nigeria were used for the study. They weighed 900, 850, 950, 880,
930, 890 and 900 g and a standard body length was measured and it amounted to
45, 48, 42, 40, 50, 44 and 46 cm. The fish were immobilized and the oropharyngeal cavity was cut open through the membrane between the upper and
lower jaws, and the specimen was dissected out. The specimen under study –
dendretic organ, was seen as an outgrowth on the dorsal aspect of the gills and it
was excised and subjected to routine histological procedure of dehydration in
graded ethanol, clearing in xylene and embedding in paraffin wax.
Sections 5 µm thick were obtained with Leitz microtome model 1512. They
were stained with haematoxylin and eosin for light microscopy examination
(Bancroft and Stevens, 1990). Photomicrographs were taken with Motican 2001
camera (Motican, UK) attached to an Olympus microscope.
Histological observations on the dendretic organ of the African catfish
141
Results and Discussion
The tubular shaped dendretic organ was covered by stratified squamous
epithelium containing mucous cells (Figures 1–2). On most surfaces, the
epithelial epithelium was organized into columns with mucous cells placed inbetween the epithelial cell columns (Figure 3). At the tip of the surface, capillaries
were lined by endothelium at the surface epithelium/air contact area (Figures 2–3).
The subepithelial layer was of loose connective tissue containing adipose tissue
and occasional blood vessels. The core of the dendretic organ contained elastic
cartilage surrounded by a dense layer of perichondrium (Figure 2). Elastic
fibres were observed in the territorial and inter-territorial spaces. Mucin
histochemistry revealed that the mucous cells contained both PAS and AB positive
mucin.
E
E
C
C
25 µm
Figure 1. Longitudinal section of the dendretic organ showing its tubular shape.
Note the covering epithelium (E) and elastic cartilage core (C).
142
Ekele Ikpegbu et al.
The stratified squamous epithelium protects the underlying structures
(Agrawal and Mittal, 1991). It also supports the surface capillaries involved in gas
exchange with atmospheric air. The epithelium stacked in columns with mucous
cells positioned in-between the columns may be an adaptation that will make the
produced mucin easily cleanse the respiratory epithelium. This column-shaped
epithelium will also allow more vascularization, since each individual column
contained capillaries at the tip of the organ/air interphase. This increases surface
area for gas exchange. The mucin, produced by the mucous cells, reduces
mechanical abrasion, thus protecting the respiratory epithelium (Elbal and
Agulleiro, 1986; Moitra et al., 1989; Ghosh et al., 2011), while acid mucin will
protect the respiratory epithelium against pathogens (Neuhaus et al., 2007). It will
also trap moisture at the respiratory epithelial surface, enhancing the rate of gas
exchange (Singh et al., 1974; Moitra et al., 1989).
P
BV
L
E
C
M
50 µm
Figure 2. Section of the dendretic organ showing surface capillaries (arrow),
mucous cells (M), epithelial cells (E), blood vessel (BV), in the loose connective
tissue (L). Note the elastic cartilaginous core (C) surrounded by fibrous
perichondrium (P).
Histological observations on the dendretic organ of the African catfish
143
The simple endothelial lined capillary is thin enough to allow a rapid
exchange of gas between blood in the capillaries and atmospheric air (Ahmed and
Mekkawy, 2011). Thus the air/blood barrier is basically the simple endothelium
and its basement membrane. This finding is consistent with the reports on other
ABOs (Munshi et al., 1986; Maina, 2002). The blood vessels in the subepithelial
region are the arteries that send branches to form the surface capillaries involved in
gas exchange. The elastic cartilage allows support and flexibility of the dendretic
organ as it has been previously reported in literature (Ahmed et al., 2008).
M
C
50 µm
Figure 3. Section of dendretic organ showing columnar shaped epithelium
containing surface capillaries (arrow) at the tip and mucous cells (M) in-between
the columns. Note the elastic cartilage (C).
144
Ekele Ikpegbu et al.
Conclusion
In conclusion, microanatomy of the dendretic organ from commercial
aquaculture reveals its adaptation to the exchange of gas from the atmospheric air.
This organ will help the fish adapt better in periods of overstocking or dissolved
oxygen deficiency in the concrete tanks. This finding will enhance our knowledge
on farmed African catfish physiology, help clinicians in disease diagnosis and form
the baseline data for further investigative research.
References
Agrawal, N., Mittal, A.K. (1991): Epithelium of lips and associated structures of the Indian major
Carp, Catla catla. Jap. J. Ichthyol. 37(4):363-373.
Ahmed, A., Mohamed, K., Ahmed, S., Masoud, F. (2008): Anatomical, light and scanning electron
microscopic studies on the air breathing dendretic organ of the sharp tooth catfish (Clarias
gariepinus). J. Vet. Anat. 1(1):29-37.
Ahmed, S.A.H., Mekkawy, A.A.I. (2011): Skin characteristics and organization of the air-breathing
fish, Alticus kirkii (Günther, 1868) along different body regions. J. Biol. Sci. 11:466-474.
Bancroft, J.D., Stevens, A. (1990): Theory and practice of histological techniques, third edition.
Churchill Livingstone, London, Toronto.
Banerjee, T.K., Chandra, S. (2005): Estimation of zinc chloride contamination by histopathological
analysis of the respiratory organs of the air breathing ‘murrel’ Channa striata (Bloch, 1797)
(Channiformes, Pisces). Vet. Arh. 75(3):253-263.
Branson, B.A., Hake, P. (1972): Observations on an accessory breathing mechanism in Piaractus
nigripinnis (Cope). Zool. Anz. Leipzig 189:292-297.
Devi, R., Banerjee, T.K. (2007): Toxicopathological impact of sub-lethal concentration of lead nitrate
on the aerial respiratory organs of ‘murrel’ Channa striata (Bloch, Pisces). Iran. J. Environ.
Health Sci. Eng. 4(4):249-256.
Elbal, M.T., Agulleiro, B.A. (1986): Histochemical and ultrastrucutral study of the gut Mugil saliens
(teleost). Acta Micros. 9(1):31-40.
Gervais, M.R., Tufts, B.L. (1998): Evidence for membrane- bound carbonic anhydrase in the air
bladder of Bowfin (Amia calva), a primitive air-breathing fish. J. Exp. Biol. 201:2205-2212.
Ghosh, S.K., Ghosh, B., Chakrabarti, P. (2011): Fine anatomical structures of the intestine in relation
to respiratory function of an air-breathing loach, Lepidocephalichthys guntea (Actinoterygii:
Cypriniformes: Cobitidae). Acta Ichtyll. Pisca. 41:1-5.
Gordon, M.S., Boetius, I., Evans, D.H., McCarthy, R., Oglesby, L.C. (1969): Aspects of the
physiology of terrestrial life in amphibious fishes: I. The mudskipper, Periophthalmus sobrinus.
J. Exp. Biol. 50:141-149.
Maina, J.N. (2002): Structure, function and evolution of the gas exchangers: comparative
perspectives. J. Anat. 201(4):281-304.
Martin, K.L.M. (1995): Time and tide wait for no fish: Intertidal fishes out of water. Envir. Biol.
Fishes 44:165-181.
Moitra, A., Singh, O.N., Munshi, J.S.D. (1989): Microanatomy and cytochemistry of the gastrorespiratory tract of an air-breathing Cobitidid fish, Lepidocephalichthys guntea. Jap. J. Ichthyol.
36(2):227-231.
Munshi, J.S., Olson, K.R., Ojha, J., Ghosh, T.K. (1986): Morphology and vascular anatomy of the
accessory respiratory organs of the air-breathing climbing perch, Anabas testudineus (Bloch).
Am. J. Anat. 176(3):321-31.
Histological observations on the dendretic organ of the African catfish
145
Neuhaus, H., Marel, M., Caspari, N., Meyer, W., Enss, M.L., Steinhayen, D. (2007): Biochemical and
histochemical study on the intestinal mucosa of the common carp Cyprinus carpio L., with
special consideration of mucin glycoproteins. J. Fish Biol. 70:1523-1534.
Park, K.Y. (2002): Structure of the skin of an air-breathing mudskipper, Periophthalmus
magnuspinnatus. J. Fish Biol. 60:1543-1550.
Sayer, M.D.J. (2005): Adaptations of amphibious fish for surviving life out of the water. Fish and
Fisheries 6:186-211.
Sayer, M.D.J., Davenport, J. (1991): Amphibious fish: Why do they leave the water? Rev. Fish Biol.
Fisheries 1:159-181.
Singh, R.R., Guha, G., Munshi, J.S.D. (1974): Mucous cells of the respiratory sac in an air-breathing
fish, Saccobranchus fossilis (Bloch). La Cellulae 70(1):5-15.
Steedman, H.F. (1950): Alcian blue 8G: a new stain for mucin. J. Micr. Sci. 91:477-479.
Taylor, D.S. (2000): Biology and ecology of Rivulus marmoratus: New insights and a review. Florida
Scientist 63:242-255.
Received: July 27, 2013
Accepted: October 18, 2013
146
Ekele Ikpegbu et al.
HISTOLOŠKA GRAĐA DENDRITSKOG ORGANA GAJENOG ODRASLOG
AFRIČKOG SOMA (Clarias gariepinus B.) IZ ISTOČNE NIGERIJE
Ekele Ikpegbu*, Uchenna Nlebedum, Okechukwu Nnadozie i
Okezie Agbakwuru
Odsek za veterinarsku anatomiju, Michael Okpara Poljoprivredeni univerzitet
Umudike, Abia State, Nigerija
Rezime
U radu se istražuje histologija dendritskog organa – pomoćnog organa za
disanje kod afričkog soma kako bi se osvetlila njegova mikroanatomija. Dobijeni
podaci će pružiti osnovne informacije za dalja istraživanja i pomoći patolozima
koji se bave ribama koje poseduju akcesorne disajne organe. Histologija je
pokazala da je dendritski organ cevastog oblika prekriven pločastim slojevitim
epitelom koji sadrži sluzne ćelije pozitivne na histohemijska bojenja PAS (perjodna
kiselina i Schiff-ov reagens) i AB (alcian plavo). Na većini površina, epitelne ćelije
su organizovane u kolone sa sluznim ćelijama koje su smeštene između nizova
epitelnih ćelija. Na samoj površini, kapilari su obloženi endotelom u blizini
kontaktne oblasti epitel/vazduh. Subepitelni sloj je sastavljen od rastresitog
vezivnog tkiva koje sadrži masno tkivo i krvne sudove koji se javljaju sporadično.
Centralni deo dendritskog organa sadrži elastičnu hrskavicu koja je okružena
gustim slojem perihondrijuma. Elastična vlakna su uočljiva u teritorijalnim i
međuteritorijalnim prostorima hrskavice.
Ključne reči: sluzne ćelije, histohemija, površinski kapilari, epitel.
Received: July 27, 2013
Accepted: October 18, 2013
*
Corresponding author: e-mail: [email protected]