Eutrophication, Ammonia Intoxication, and Infectious Diseases: Interdisciplinary Factors of Mass Mortalities in Cultured Nile Tilapia

Abstract

The present study was designed to assess the possible causes of the mass mortalities of Nile Tilapia Oreochromis niloticus at El-Behera Governorate, Egypt, in relationship to environmental and microbiotic factors. Water samples were collected from fish farms at different locations and from Lake Edku to analyze water temperature, water pH, salinity, biological oxygen demand, dissolved oxygen, total ammonia nitrogen, and un-ionized ammonia. A number of moribund and freshly dead fish were sampled and submitted to our laboratory for microbiological, molecular, and histopathological examination. Water analysis of the fish farms revealed noticeable increases in the previously mentioned physicochemical parameters. Clinical examinations of moribund fish showed severe gill rot and massive external and internal hemorrhages. Ordinary and molecular laboratory findings confirmed the presence of Branchiomyces sp. in gill tissue and mixed bacterial fish pathogens (Streptococcus agalactiae, Vibrio alginolyticus, V. parahaemolyticus, Pseudomonas anguilliseptica, and P. aeruginosa) in visceral organs. The histopathological and transmission electron microscopic examinations revealed severe necrosis of gill filaments and blockage of branchial blood vessels and lamellar capillaries with Branchiomyces sp. hyphae and spores mixed with different shapes of bacteria. Severe inflammations were detected in liver, kidney, heart, and brain tissues. Ultimately, we can conclude that the syndrome of mass fish kills in this area is a consequence of ecological damage to the aquatic environment, which is mainly related to natural and anthropogenic factors, as well as to the presence of infectious agents. Received September 30, 2015; accepted April 12, 2016.

Dietary administration of probiotics modulates non-specific immunity and gut microbiota of Nile tilapia (Oreochromis niloticus) cultured in low input ponds

“…Although low input systems are well established in many parts of the world [3][4][5], previous studies have indicated that only 5-15% of the nutrients input in fertilized pond systems are converted to harvestable products leading to excess nutrients in form of Nitrogen (N), Phosphorus (P) and organic matter [6]. These excess nutrients usually result from feed remnants, faeces and excreta and often lead to eutrophication, water quality problems, physiological stress, high susceptibility to pathogens and mortality of the cultured fish [7][8][9][10]. Additionally, pathogenic bacteria can also be introduced into the culture environment via organic manure, through incoming water and feeds exposing fish to infections [11].…”

Haemato-immunological responses and effectiveness of feed-based bivalent vaccine against Streptococcus iniae and Aeromonas hydrophila infections in hybrid red tilapia (Oreochromis spp.)

“…To date, vaccinated tilapia showed a significant increase of lysozyme activity compared to the unvaccinated fish in both pre-and post-infection. Subsequently, previous reports show that the lysozymes activity was significantly higher in vaccinated than unvaccinated tilapia on 3 weeks post-vaccination [67]. In contrast, Silva [68] and Pereira [26] reported, the lysozyme activity did not show a significantly different effect after post-vaccination compared with unvaccinated.…”

Eukaryote microbes potential for bioflocs in the swamp aquaculture

“…Fungi grew on the culture dish were still unknown. Branchiomyces are fungi with negative character causing the mass mortality in tilapia pond culture even the dissolved oxygen level is still above 4 mg/L (Abu-Elala et al, 2016). It is important to ensure that the fungi characteristics isolated from the locations were not pathogenic, toxic, or containing the anti-nutrient substances.…”