Studi Perbandingan Histologi Kulit Clarias gariepinus dan Oreochromis niloticus A Comparative Histological Study of Skin in Clarias gariepinus and Oreochromis niloticus

This study aimed to evaluate the comparative of histological figures in Clarias gariepinus and Oreochromis niloticus skin. A total of 18 samples were observed and collected the skin preservation. The hematoxylin-eosin staining performed to determine the histological structure. Results showed that there were different structures in the epidermis and dermis layer between C. gariepinus and O. niloticus skin. Club cells showed dominated in the epidermis layer of C. gariepinus. The pigmented cell showed clearly in the basement layer of C. gariepinus compared to O. niloticus. Stratum 91 Khairani et al. MKH (2021). 90-96 DOI: 10.20473/mkh.v32i2.2021.90-96 ©2021. Khairani et al. Open access under CC BY – SA license, doi: 10.20473/mkh.v32i2.2021.90-96 Received: 25-04-2021, Accepted: 08-05-2021, Published online: 24-05-2021 Available at https://e-journal.unair.ac.id/MKH/index compactum in O. niloticus also showed more tightly arranged compared than C.


INTRODUCTION
African catfish (Clarias gariepinus) is the result of interbreeding between female catfish C. fuscus native to Taiwan and male C. mossambicus originating from Africa and growing so fast (Dauda et al., 2018). In fact, C. gariepinus does have superior characteristics, can grow rapidly and reach large sizes in a shorter time than local catfish (Fauji et al., 2018). The number of eggs of C. gariepinus can reach 30,000-40,000 eggs / kg of female parent, while local catfish is only 1,000-4,000 eggs per kg of female parent (Hassan et al., 2018). Therefore, C. gariepinus is widely cultivated by the community today. Moreover, the consumption of catfish from year to year is increasing (Engle et al., 2020).
Tilapia (Oreochromis niloticus) is also a freshwater fish that has a high consumption rate. O. niloticus is in demand by the public because the meat is dense, thick and the price is relatively cheap (Suryani and Arya, 2017). O. niloticus cultivation is faced with the constraints of high feed costs and long cultivation times (Effendi et al., 2020).
In general, vertebrate skin consists of several layers, with two main layers i.e. the outer layer called the epidermis layer and the inside is called the dermis layer. The epidermis layer in fish always looks wet because of the mucus produced by the cup-shaped cells that are found all over the body surface (Romano et al., 2019). In the dermis layer there are blood vessels, nerves, and connective tissue. O. niloticus skin has a high collagen content. Collagen is a fibrous protein which is the main component of connective tissue and is the most abundant protein in mammals. Collagen is also found in bones, tendons, skin, blood vessels and corneas (Zhou et al., 2017). This study was conducted to evaluate the differences in the histological structure of the skin of C. gariepinus and O. niloticus.

Ethical approval
The ethical approval for this study was not required due to in accordance with the native protocol in fish skin preservation.

Samples
A total of 18 samples C. gariepinus and O. niloticus were used as samples. All samples were reared in a different pond with standard protocol. This study conducted for 40 days to obtain the age of adult fish. The skin sample collected from adult fish using a blade surgery along 2 cm x 2 cm. A 15% of formaldehyde used for the fixation solution for each collected sample.

Hematoxylin-eosin (HE) staining
The skins were stored in formaldehyde 15% for 48 h. Furthermore, alcohol was used as a dehydration agent with concentration of 70%, 80%, and 96%. Xylol was used for the clearing process and continued making paraffin block at a temperature of 60°C. The skin tissue that has received paraffin blocks then sliced using a microtome machine and then transferred into a water bath before being placed on a glass object. The HE staining performed for 2 h then mounting the glass object for further observation (Purnama et al., 2019).

Data analysis
This study evaluated descriptively and observed using Binocular Microscope (LED CX22, Olympus). The histological figure captured in 100, 400 and 1000 magnification.

RESULT
Based on the results of microscopic observations, the skin of C. gariepinus and O. niloticus consists of the epidermis, dermis, and hypodermis layers ( Figure  1A-B). Pigment cells on the dorsal part of C. gariepinus are more commonly found than O. niloticus. Pigment cells appear blackish-brown on the dorsal and brown on the abdomen. In addition to providing a color pattern to fish skin, pigment cells also function to absorb and reflect radiation thereby contributing to regulating body temperature in fish. The dermis layer of both fish skin is composed of connective tissue, blood vessels, pigment cells and fat tissue ( Figure 1C-D). Mucus cells on the dorsal part of O. niloticus skin are more commonly found than C. gariepinus ( Figure 1E-F).

DISCUSSION
The epidermis layer consists of stratified squamous epithelial cells, mucus cells, club cells, and pigment cells (Dash et al., 2018). The basement layer of the epidermis is called the stratum germinativum.
The constituent epithelium of this layer is composed of basal cells. There are no blood vessels in the epidermis layer. In accordance with the statement of Tiralongo et al. (2018), that the blood vessels are not found in the epidermis layer, thus the metabolic needs are obtained by diffusion.
The thickness of the epidermal layer varies greatly depending on the part of the body, age, sex, stages of the reproductive cycle, and environmental conditions (Lauder et al., 2016). The fish epidermis layer consists of squamous and cuboidal epithelial cells, mucus cells, lymphocytes, macrophage cells, and specific cells in certain fish species (Brinchmann, 2016). The epithelial cells in fish skin are active metabolic tissues. The outer epithelium of the fish skin is very actively proliferated so that it is reformed regularly and always maintains a balance between proliferation and differentiation (Wainwright and Lauder, 2017).
Mucus cells have a role as a lubricant for the surface of the skin, the mucus produced can act as a deterrent to the entry of various pathogens and their colony formation in the epidermis. Mucus acts as a lubricant to reduce body surface friction in the water, helps in swimming and also protects the body from abrasion when digging nests (Reverter et al., 2018). Excessive mucus secretion occurs in fish that live in hiding and muddy dwellings. Mucous cells can be distinguished from the basal epidermis and then as they increase in size they move towards the surface where they secrete their fluid (Guardiola et al., 2016).
Club cell functions as a chemical alarm that gives a signal if there is a threatening danger or often called "alarm cell". These cells will burst when there is a threat from a predator and will release pheromones that produce a fear reaction when the skin is physically damaged, thereby triggering an avoidance response E F to the predator. Club cells help in the healing of epithelial cells and mucosal cells that are damaged during injury caused by pathogenic agents (Rasmussen and Sagasti, 2018).
The dermis is divided into two parts i.e. the stratum spongiosum on the outside and the stratum compactum on the inside. In the stratum spongiosum that leads to the relatively loose part of the epidermis, it is composed of fatty tissue, blood vessels, and there is also collagen connective tissue. Stratum compactum is found collagen connective tissue that is arranged regularly and is thicker (Drelich et al., 2018).
Collagen fibers are scattered in the dermis layer of the skin, in the stratum spongiosum the collagen fibers are looser, while in the stratum compactum the collagen fibers are very tightly arranged (Arumugam et al., 2018). On the dorsal skin, the collagen fibers are thicker than in the abdomen based on the thickness of the stratum compactum. Apart from being rich in collagen, the dermis layer is where the scales form in fish. The scales form in the dermis so that they are termed the dermis skeleton, and usually, the scales are covered by epidermal tissue (Ali et al., 2018).

CONCLUSION
In conclusion, based on this finding there was a comparative morphology on the epidermis layer between O. niloticus compared to C. gariepinus. Mucus cell and club cell showed adequately in the epidermis layer of O. niloticus.
In contrast, only club cells showed dominated in the epidermis layer of C.

gariepinus.
On the other hands, pigmented cell showed clearly in the basement layer of C. gariepinus compared to O. niloticus.

Authors
acknowledge the Banyuwangi fish farmers community for their support during collected samples and also laboratory PSDKU Banyuwangi for providing facilities during study.