In 2016, Barramundi, Lates calcaifer juveniles imported from Thailand to the aquaculture station at Sultan Qaboos University exhibited remarkable external clinical signs of losing scales, severe muscle necrosis, and ascites. Fin rot was also observed in the diseased fish. The mortality reached more than 90 % and it was assumed that certain bacterial species were associated with the diseased fish. The objective of the present study was to investigate the infection route of disease, revealing the causative agent and finding the most effective antibiotic treatment. The suspected pathogen vehicle was mosquito larvae in the outlet of the culture tank as bacterium was isolated inside the mosquito larvae. Primary, traditional phenotypic tests and the vitic test confirmed that the bacteria were pathogenic Aeromonas sobria and Lactococcus garvieae. Eight of the most commonly used antibiotics in the aquaculture industry was used for antibiotic susceptibility test. It showed that that Gentamycin was the most effective antibiotic while the most effective environmentally friendly source was henna, Lawsonia inermis, at a concentration of 10%.

Aphanius dispar (Rüppell 1828) (Pisces: Cyprinodontidae), is common and widely distributed in fresh and brackish water of the Middle East. Few studies were conducted on the structures of this fish organs. This study aimed to look at the structure of the ovary.The fish were collected and transported into the Biology Department, Sultan Qaboos University. The fish were killed by placing them in ice for few minutes. Then they were dissected out for their gonads. The gonads have whitish color and are located in one side of the abdomen. The gonads were fixed in Karnovsky buffered with sodium cacodylate to a pH of 7.4 for four hours and then cut into small pieces. The tissue were washed in cacodylate buffer and then post-fixed in 1% aqueous solution of osmium tetroxide for 1 hour and dehydrated in a series of alcohol before embedding in Agar 100 resin. Semi and ultra-thin sections were cut using Reichert ultramicrotome. The semi-thin sections were stained with toluidine blue and the sections were examined using a Nikon 104 light microscope. The ultra-thin sections were stained with uranyl acetate and post-stained in lead citrate. They were examined under JEOL JEM -1230 TEM.The ovary show different stages of the oocytes development. Three different stages of the development of the oocyte were seen; previtellogenesis, vitellogenesis and maturation ( fig. A). Each oocyte is surrounded by follicle cells and by rough layers called zona radiata (fig. B). Follicle cells are irregular in shape with large nuclei. The Zona radiata (zona pollucida in mammals) is located between the follicle cells and the cytoplasm of the oocyte. It has a large number of pores ( fig. C). The oocyte has a spherical nucleus, a number of smooth endoplasmic reticulum, Golgi complex and mitochondria ( fig. D).

In 2016, Barramundi, Lates calcaifer juveniles imported from Thailand to the aquaculture station at Sultan Qaboos University exhibited remarkable external clinical signs of losing scales, severe muscle necrosis, and ascites. Fin rot was also observed in the diseased fish. The mortality reached more than 90 % and it was assumed that certain bacterial species were associated with the diseased fish. The objective of the present study was to investigate the infection route of disease, revealing the causative agent and finding the most effective antibiotic treatment. The suspected pathogen vehicle was mosquito larvae in the outlet of the culture tank as bacterium was isolated inside the mosquito larvae. Primary, traditional phenotypic tests and the vitic test confirmed that the bacteria were pathogenic Aeromonas sobria and Lactococcus garvieae. Eight of the most commonly used antibiotics in the aquaculture industry was used for antibiotic susceptibility test. It showed that that Gentamycin was the most effective antibiotic while the most effective environmentally friendly source was henna, Lawsonia inermis, at a concentration of 10%.