• Journal of fish pathology
• /
• v.28 no.3
• /
• pp.145-155
• /
• 2015

The pathogenecity of atypical Aeromonas salmonicida was studied in healthy Oreochromis niloticus. Inoculum at concentration of $1.5{\times}10^8CFU/ml$ and $3{\times}10^8CFU/ml$ was injected into healthy fish through intramuscular and intraperitoneal injections. Experimentally infected Oreochromis niloticus showed ulceration at the dorsal musculature and trunk region in addition to black coloration, congested gills, exophthalmia, and ocular hemorrhage. Congested liver and kidney were recorded in post-mortem examination. Mortality of the experimentally infected Oreochromis niloticus reached 100% after intramuscular injection at concentration of $3{\times}10^8CFU/ml$. Histopathological investigation of infected organs was also performed. There was a focal area of bundles of skeletal musculature showing hyalinization. In addition, hyperplasia, congestion, and fusion were noticed in the gill lamellae. There was also congestion in the blood vessels in the ocular chamber. Severe congestion was also noticed in the central vein of liver associated with focal aggregation of the melanin pigmented cells in the parenchyma. Degenerative changes were noticed in the epithelial cells lining of kidney tubules. Plant extracts carvacrol and its biological precursor cymene were found to be effective in treating experimentally infected Oreochromis niloticus at concentration of 100 or 200 ppm.

• Interdisciplinary Bio Central
• /
• v.2 no.4
• /
• pp.10.1-10.5
• /
• 2010

Total aflatoxin and ochratoxin were detected in 3 naturally contaminated fish feed samples using immune-affinity method. The results revealed that the average levels of aflatoxins in the 3 examined samples were (15, 22 and $12\;{\mu}g/kg$) respectively while the average levels of ochratoxins were (15, 6 and $6\;{\mu}g/kg$). The results of determination of the effects of clay as a mycotoxin binder on the health status and performance of Oreochromis niloticus in comparing with a control group revealed that the survival rate in control group was 81% after the end of the culture season. The results also revealed that the survival rate in group 2 which received clay treated feed was 86%. The results of regular parasitological examination revealed the identification of trichodina as external protozoa in Oreochromis niloticus from both ponds but without manifestation of disease signs. The results of bacteriological examination revealed the isolation and identification of Pseudomonas flouresence from some moribund Oreochromis niloticus. Higher performance parameters were recorded in group 2 that received feeds treated with clay which reflected in the total production which reaches 1646.47 kg while in the control pond, the total production was1308.36 kg.

• Fisheries and Aquatic Sciences
• /
• v.25 no.1
• /
• pp.20-30
• /
• 2022

The present study was carried out to investigate the food and feeding habits of Oreochromis niloticus in Lake Shala to manage this species in this high Soda Lake. Stomachs of 226 fish (65.9%) had different food items, while those of 117 fish (34.1%) were empty. Phytoplankton was the dominant food categories occurring in 90.3% of the stomachs estimated and contributed 75.5% of the total volume. Bacillariophyceae (Nitzschia, Anomoeoneis, Navicula and Melosira) were identified as the most desired phytoplankton item. The prey items of O. niloticus differed among size classes (ANOVA, p < 0.05). The main prey items were zooplankton by the smaller-size class, and phytoplankton in fish of the larger-size class. Seasonal variation in the diet composition was evident (t-test, p < 0.05) and zooplankton, chironomids, nematodes, fish scales and detritus were important during the wet season, while phytoplankton predominates during the dry season. This study concludes that O. niloticus had a phytoplanktivores feeding mainly on phytoplankton and their feeding habits influenced by season and fish size in Lake Shala.

• Fisheries and Aquatic Sciences
• /
• v.26 no.8
• /
• pp.514-523
• /
• 2023

The visible threshold of Oreochromis niloticus responded to high light intensity under short wavelengths, whereas the response to low light intensity under long wavelengths was low, with a minimum visual threshold of 574 nm of LED lights. Movement distance of O. niloticus was dropped at 31℃ and increased abnormally at 37℃ under natural light. Comparing movement distance under red (622 nm) and green (518 nm) lights of LED, movement distance and swimming speed under red and green lights were higher than under natural light. However, the movement distance decreased rapidly at 31℃ under red light and lowest at 33℃ under green light. After that, there was a tendency to adapt to high water temperatures gradually. Consequently, red and green lights may be recommended for O. niloticus's aquaculture because the red and green lights have a positive effect on growth performance, survival rate, and metabolism, as shown in previous studies. It is necessary to control the water temperature below 32℃ because abnormal behavior above 32℃ revealed under red and green LED lights and natural light.

• Journal of fish pathology
• /
• v.30 no.1
• /
• pp.11-24
• /
• 2017

The current investigation dealing with the causative agent of mass mortalities in cultured Oreochromis niloticus. The diseased fish showed external hemorrhage, unilateral and bilateral eye opacity, ended by blindness and fish death. The postmortem lesions revealed congested friable kidney and spleen, and liver has yellow nodules. Obtained isolates were identified as Aeromonas hydrophila (the causative agent of Motile Aeromonas Septicemia) and found to be highly pathogenic as they contained hemolysin virulence gene causing mortality reached to 100 and 70% in intraperitoneal and intramuscular infection. The prevalence of MAS was 80% among the surveyed O. niloticus. Blood and serum were collected from naturally diseased, intraperitoneal and intramuscular injected O. niloticus for hematological and biochemical examination. Similarly, gills, musculature, kidney, liver and spleen were collected for histopathological evaluation, and micropathomorphological analysis of spleen was done. Macrocytic hypochromic anemia was recorded in the intraperitoneal infection. Serum protein, albumin and globulin were decrease only in naturally diseased fish. Leucocytosis with heterophilia and lymphocytosis were observed in naturally diseased and intraperitoneal infected fish. There were severe degenerative changes and hemorrhagic necrosis in the examined tissues which were more obvious in intraperitoneal than intramuscular infection. Activation and proliferation of melanocytes macrophages centers with severe hemosiderosis were recorded in spleen of naturally diseased and experimentally infected fish.

• Korean Journal of Animal Reproduction
• /
• v.16 no.4
• /
• pp.377-385
• /
• 1993

This study was taken to examine correlationships between ehdocrine changes such as estradiol-17$\beta$, progesterone, T4 and T3 and serum components concentrations of female Oreochromis niloticus living in 0$\textperthousand$, 10$\textperthousand$, 20$\textperthousand$, and 30$\textperthousand$ salt concentrations, respectively. The results obtained in these experiments were summarized as follows. Correlation coefficients of serum albumin and thyroxine were ＋0.907 and ＋0.611 in 10$\textperthousand$ and 20$\textperthousand$, respectively. In 30$\textperthousand$ salinity, serum BUN and other 3 kinds of hormones showed all negative correlation coefficients. Correlation coefficients of serum estradiol-17$\beta$ with calcium and cholesterol in 20$\beta$ were ＋0.624, ＋0.733, respectively. Correlation coefficient between serum triglycerides and thyroxine in 30$\beta$ was ＋0.989.

• Fisheries and Aquatic Sciences
• /
• v.26 no.8
• /
• pp.491-499
• /
• 2023

Lake Tinisu Abaya is home to some fish species. The lake's native fish species include Barbus and Tilapia zilli. Tilapia fish (Oreochromis niloticus L.) were stocked in Lake Tinishu Aabaya in 1997. This study aimed to investigate the feeding behaviors of O. niloticus in Lake Tinishu Abaya to develop an appropriate fisheries management approach in the lake. 428 O. niloticus fish samples (2.5 to 30.9 cm and 1.1 to 475 g) were collected to calculate the diet composition. Out of the total of 428 gut contents examined, 55 (12.85%) were found to be empty and 373 (87.15%) to be containing one or more food items. The diet behavior of the stocked fish in the study lake revealed that phytoplankton (39.5% by volume) and macrophytes (25.81% by volume) were the most noteworthy food items followed by detritus (14.39%) and zooplankton (12.95%). With increasing fish size, the importance of phytoplankton, macrophytes, and detritus increased while the contribution of zooplankton, insects, and other foods with an animal origin decreased. Seasonal variation in the diet composition of fish was evident (t-test; p < 0.05). Macrophytes, zooplankton, and detritus were the dominating food items during the wet season, while phytoplankton predominated during the dry season. This study demonstrated that O. niloticus had phytoplanktivores that primarily consumed phytoplankton and that the seasons and fish size had a significant impact on their feeding preferences. The diet of O. niloticus in Lake Tinishu Abaya comprised foods with both plant and animal origins. It concludes that the dietary habit of O. niloticus in the lake is, generally, the omnivorous type.

• Journal of Aquaculture
• /
• v.8 no.2
• /
• pp.77-83
• /
• 1995

The effects of six levels (0, 5, 10, 15, 20, and 25 ppm) of dietary $17\alpha-Methyltestosterone$ (MT) on sex reversal and growth of Oreochromis aureus (Steindachner) and O. niloticus (L.) were evaluated. Fifteen ppm MT produced $100\%$ male populations in both species. Both MT-treated and untreated O. niloticus grew significantly faster than their O. aureus counterparts (P<0.05).

• Fisheries and Aquatic Sciences
• /
• v.13 no.4
• /
• pp.343-349
• /
• 2010

The effects of osmotic stress on the non-specific immune response of Nile tilapia, Oreochromis niloticus, were investigated. Osmoregulatory mechanism of tilapia has been studied, but less information is available about innate immune response of O. niloticus faced with hyperosmolality. Acute osmotic stress was elicited by transferring tilapia from freshwater (FW) to 24 psu seawater (SW). Non-specific immune parameters including lysozyme activities of plasma and head kidney (HK), alternative complement pathway (ACP) activity in plasma, phagocytic capacities of spleen and HK immune cells, and respiratory burst activity of immune cells in both HK and spleen were analyzed. Lysozyme activities were increased at 1 h and 30 h after transfer to SW, but decreased at 10 h after SW transfer. Conversely, ACP activity increased 10 h after SW transfer. Phagocytic capacity increased slightly at 1 h and 5 h after SW transfer, and respiratory burst activity showed an increase in superoxide release at 10 h after SW transfer. Taken together, these results indicate that the exposure of tilapia to hyperosmotic conditions has immunostimulatory effects on cellular and humoral immune reactions.

• Fisheries and Aquatic Sciences
• /
• v.15 no.4
• /
• pp.305-311
• /
• 2012

We investigated compensatory growth of Nile Tilapia Oreochromis niloticus in structural size and live weight in response to different deprivation periods and refeeding. Four treatments were assigned randomly to fish in 12 glass tanks, with each treatment performed in triplicate. The control group was fed to satiation three times a day throughout the experiment. The other three treatment groups were starved for 1 week (S1), 2 weeks (S2), or 4 weeks (S4) and then fed until the end of the experiment. After the experiment, no significant differences were observed among S1, S2, and the control group in average weight or length, whereas the weight and length of S4 were significantly reduced. Relative condition factors of the three starved groups decreased significantly until the end of the restricted period but recovered rapidly after refeeding. The specific growth rate in weight ($SGR_W$) of the three restricted groups recovered quickly upon refeeding and were significantly higher than the control group, but these differences disappeared gradually until the end of the experiment. No significant difference in specific growth rate in length ($SGR_L$) was noted between the control group and the three restricted groups after refeeding. All three groups showed hyperphagia for a short period upon refeeding, and no statistical differences were observed in feeding efficiency among the four groups.