Aquaculture: Image analysis used to measure morphometric characteristics of nuclei and nucleoli of hepatocytes from pejerrey fish
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The pejerrey (Odontesthes bonariensis) it is one of the most important commercial and sport freshwater fishing resources in the Pampean Region of Argentina. It is one of the few autochthonous species in which attended fecundation is carried out for seeding and repopulation.
This fact and the established internal market are the foundation of the future development of an extensive and semi-intensive aquaculture project. The interest of the Japanese people toward this species, has led to the establishment of commercial intensive factories in their territory, enhancing the development of numerous fecundation techniques and research lines oriented to the physiology and pathology of the Pejerrey.
A work carried out by Strьssmann and Takashima (J.Fish.Biol. 36:59-65, 1990) has shown that starving larvae of pejerrey presented a significant decrease of the nuclear area of the hepatocytes when compared with control larvae. This observation takes relevance considering its possible use as an indicator of the nutritional state of a natural population since it is constant, easy to obtain and has low cost.
Without doubt, the sanitary state of the fish should be the base for the possible commercial development in our region. For that reason, and as part of an integral project of evaluation of the fishing resource of the Laguna Salada Grande of Madariaga (Buenos Aires, Argentina), seasonal samplings were carried out during two years. During this period, significant decreases of the K index of condition (Lst3 / W) were detected between the two winter seasons (Fig. 1).
Fig. 1 Condiction Index K of females obtained between 2 winter seasons in the Laguna Salada Grande of Madariaga.
With the purpose of validating the observations carried out by Strussman but in mature fish, liver samples of female Odontesthes bonariensis, coming from the two aforementioned seasons, were compared.
Random images of the hepatic tissue were captured from a microscope (Olympus BX50, Tokyo, Japan) with a microscopic magnification of 100x (Fig. 2), through an attached analogical RGB videocamera (Sony DXC-151A CCD, Tokyo, Japan). The images were then digitized with a frame grabber (Flashpoint 128, Integral Technologies Inc, Indianapolis, IN, USA) connected to the computer (PC Pentium II, 266 MHz, 64Mb RAM) and analyzed with software: Image-Pro Plus for Windows95 v3.01 - Media Cybernetics, Silver Spring, MA, USA). Images were captured with a pixel depth of 24 bits RGB in the TIFF format.
The resolution was set to 640x480 pixels and the corresponding yield was 0.126 µm/pixel. Images were then converted to a 8 bit grey scale. To delineate the nuclei and nucleoli of the hepatocytes, the histogram based option of Image-Pro's Color Segmentation process was applied. Standard measurements (area, aspect, major and minor diameter and roundness) were then performed. The obtained results have shown a highly significant statistical difference between both groups of female fish.
Fig. 2. Nuclei and nucleoli of hepatocytes of well-fed fish (top) are compared to starving pejerrey's hepatic cells (bottom). X100.
Researchers: Nicolas Garcнa Romero, Eduardo Juan Gimeno, Enrique Leo Portiansky
Dr. Enrique Leo Portiansky
Instituto de Patologia
Facultad de Ciencias Veterinarias
Universidad Nacional de La Plata
Calle 60 y 118
1900 La Plata
Tel: + (54)(21) 83-6880 ext 51
Fax: + (54)(21) 25-3276/7980