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Transmission and Pathology of Streptococcus Inane in Monosex Nile Tilapia (oreochromis Niloticus) in Aquaculture of Bangladesh

Md. Mer Mosharraf Hossain
Department of Fisheries and Marine Bioscience, Jessore University of Science and Technology, Jessore-7408, Bangladesh

Amimul Ehsan
South-West Area Integrated Water Resources Planning and Management Project, Bangladesh Water Development Board, Bangladesh

Md. Anisur Rahman
Department of Fisheries and Marine Bioscience, Jessore University of Science and Technology, Jessore-7408, Bangladesh

Monjurul Haq
Department of Fisheries and Marine Bioscience, Jessore University of Science and Technology, Jessore-7408, Bangladesh

Md. Bazlur Rashid Chowdhury
Department of Aquaculture, Bangladesh Agricultural University, Mymensingh, Bangladesh

Abstract/ Executive Summary:

Streptococcus iniae is a major fish pathogen, recently emergent outbreaks were recorded in commercially cultured monosex Nile tilapia (Oreochromis niloticus) result in significant losses termed “streptococcosis”- causes unusual appearances with multi-focal pin-point haemorrhages, abscesses, necrosis and ascites in skin, fin, muscle, liver, spleen, kidney, blood, interstitial fluid specially in central nervous system and brain. This disease was more prevalent (>26%) at summer when the water temperature was approximately >25^oC, percentage of mortality was higher >41% during the overcrowding and improper water chemistry. Raised levels of glucose and ammonium in blood serum causes reduced number of free blood cells released into the haemolymph to stomach and gut, result in refrain from eating in diseased tilapia. Stocking density (200 fish/decimal; class IV) had significant effect (P<0.01) on the total production (5,000 to 5,500 kg/ha). S. iniae in the circulating blood cells, extra-tubular haemal spaces containing blood vessels, fixed phagocytes in the hepatopancreas (gastrointestinal tract), bacteria-like particles in the brain tissue, vacuum and necrosis in hepatocytes revealed with histopathology. In vitro study revealed that cohabitation of dead or infected fish with healthy fish resulted infection (horizontal transmission mechanism) to the healthy fish.

Keywords: Streptococcosis, Monosex tilapia, Histopathology, Transmission

Location: Department of Fisheries and Marine Bioscience laboratory, Jessore University of Science and Technology and Faculty of Fisheries, Bangladesh Agricultural University

Start Date:

End Date:

Program Area: Animal Health and Management

Commodity: Tilapia

Objectives:

The present study also aims to evaluate the growth performance of the all-male Nile tilapia population at various stocking densities and determine an ideal stocking density as well as appropriate water quality under the climatic and ecological conditions prevailing in the cultured systems in southern part of Bangladesh.

Methodology:

Experimental fish and deign: Adult tilapia (Oreochromis niloticus) affected by satreptococcal disease were collected from Naoili, Bisali, Kashipur, Chachuri, Kalia, Shingashul in Jessore and Narail districts (arrow indicates the working area in map; from a pilot farm of South-West Area Integrated Water Resources Planning and Management Project (SAIWRPMP) funded by Asian Development Bank (ADB), Ministry of Water Resource and Bangladesh Water Development Board (BWDB) during the period of 2012-2013. Independent experiments were designed in vitro at the Department of Fisheries and Marine Bioscience laboratory, Jessore University of Science and Technology and Faculty of Fisheries, Bangladesh Agricultural University, to evaluate the health, dietary needs, density, dose of tilapia (diseased or disease-free) at different replicable stocked such as: 80, 120, 160, 200, 240 and 280 fry/decimal corresponding to density classes (I, II, III, IV, V and VI), bacterial strain, infection trails and histopathology. Health status assays: Blood and interstitial fluid (haemolymph) was withdrawn from tilapia, O. niloticus by puncturing the unsclerotized membrane with a 21 gauge needle and syringe. For total haemocyte (blood cell) counts (THC), the blood was mixed with an equal volume of ice-cold fixative (5% formaldehyde in 3% sodium chloride solution) and cells counted with a Neubauer haemocytometer. For blood chemistry (total protein, ammonium and glucose) blood was allowed to clot for 60 min on ice, centrifuged (5000 g; 10 min) and the resulting serum stored at -80⁰C. Total protein was determined using a bicinchromic acid assay kit (Pierce and Warriner) using BSA as a standard, while glucose and ammonium concentrations were determined using methods (Bergmeyer 1984, Bolz and Howel 1978) modifications. Glycogen levels of the hepatopancreas (digestive gland) were determined using the anthrone method (Van Handel 1965) with type II glycogen (Sigma- Aldrich) as the standard. All assays were performed in 96- well microtitre plates and absorbance’s read on an Anthos II plate reader.Culture pond: Fifty newly excavated 0.02 to 0.05 ha freshwater earthen ponds were completely drained, tilled, dried, leveled and limed at the rate of 247 kg/ha during the sunny days after plowing. Ponds limed and one week later water level was increased up to 1.37 m to support natural productivity. Organic fertilizers (cattle manure 1235 kg/ha and compost 1235 kg/ha) and inorganic fertilizers (urea and TSP; 24.7 kg/ha) were applied in time intervals (15 days) during the culture period. Monosex Nile tilapia production: Three days old mixed sex juveniles of Nile tilapia (mean weight 0.0021±0.005 g; mean length 1.20±0.010 cm) were collected from the hatchery. Fish stocked in each of the culture systems at a density of 50 individuals/m3 and reared for four months. The fish were fed with 17α-methyltestosterone (17αMT) hormone treated diet (35% protein) with a dose of ≤60 mg MT/kg feed at a rate of 50%, 30% and 20% body weight/day for 21 days (Haylor and Pascual 1991, Popma and Green 1990) and other report showed 10 mg MT/kg feed at a rate of 20% body weight/day for 30 days (Chakraborty et al. 2007, Chakraborty and Banerjee 2009) and hormone treated diets were prepared by the 99% ethyl alcohol evaporation technique (Shelton et al. 1978).Statistical analyses: Duncan’s multiple tests (at 5%) were applied to evaluate the differences among means and due to dose, density and dose by density interactions (Duncan 1955). The data between treatment groups were represented as means±SD and analyzed by one-way analysis of variance (ANOVA) and Tukey’s test was used to compare the mean values between individual treatments (Zar 1984) using Stat Plus 2007 professional.

Source of Information: J Fish 2(1): 90-99, Apr 2014

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The number of S. iniae or dose used in the cohabitation experiment (cannibalism) and seasonal effect was properly quantified for streptococcal outbreaks. Stocking density (49400 fish/ha; class IV) had significant effect (P<0.01) on the total production (5,000 to 5,500 kg/ha) and average weight 300 to 320 g and also showed the highest weight, length, RGR, SGR, PER and protein content. High density (100 fish/4 l tank) effect on route of infection i.e., percentage of mortality was 41.3(±7.3), low density (25 fish/4 l tank) showed the percentage of mortality was 4.8(±0.8). Reducing fish density may be another management strategy to limit transmission of S.iniae in intensively farmed tilapia. This disease was more prevalent (>26%) at summer when the water temperature was approximately >25^oC, percentage of mortality was higher >41% during the overcrowding and improper water chemistry. Raised levels of glucose and ammonium in blood serum causes reduced number of free blood cells released into the haemolymph to stomach and gut, result in refrain from eating in diseased tilapia. The transmissions routes of infection, reduced free blood cell numbers and total serum protein, raised levels of glucose and ammonium in blood and histopathological observation suggested adequate control measures and a best management strategy should be employed to quickly remove dead and moribund fish from intensive culture operations. Reducing fish density, lowering water temperature, stopping overfeeding and water exchange also suggested a new approach for management strategy to limit transmission of S. iniae in intensively farmed tilapia.

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