Phytoplankton community composition, density, and succession were studied in tropical commercial ponds with euryhaline tiger shrimp (Penaeus monodon Fabricius) using green-water technology at two different stocking densities [T 1 10 post-larvae (PL) m −2 and T 2 15 PL m −2 ] in one grow-out season (May-October 2005) in Leganes, Iloilo, Philippines. Weekly qualitative and quantitative analyses of phytoplankton were done along with physicochemical analyses of the pond waters. A total of 103 taxa belonging to nine different algal classes were observed. Of these classes, the Chlorophyceae, Cyanophyceae and Bacillariophyceae constituted the great bulk of the phytoplankton population. The two treatments did not show any significant differences in the growth pattern of phytoplankton over time and in their diversity indices. Although T 2 had higher values than T 1 for algal density and species diversity index, the differences were not significant. The mean Shannon-Wiener diversity index for T 2 (1.56) was higher than T 1 (1.39) but not significantly different. Both treatment ponds had Chlorophyceae as the dominant algae during the initial culture phase [0-35 days of culture (DOC)], which coincided with high salinity (average= 35.67 ppt) and relatively high N:P ratios (average=1.95). The chlorophycean bloom was made up mostly of Nannochloropsis sp. The cyanophycean bloom occurred towards the final culture phase (84-112/126 DOC) when there was low salinity (average=19.5 ppt) and relatively high N:P ratios (average 2.01). A short diatom bloom occurred in T 2 at the same time that the N:P ratios rose dramatically to 4.2 at 42 DOC. Among the eight physicochemical parameters examined, positive correlations were noted among alkalinity, ammonium-nitrogen, nitrite-nitrogen and phytoplankton community. High species diversity index and species richness could have enhanced the stability of favorable Nannochloropsis blooms, especially in T 2 . No differences were noted between the two treatments in terms of the shrimp's biomass at harvest time (T 1 =28.9 and T 2 =29.4 g fresh wt per shrimp), although a significantly higher survival rate (P<0.05) was observed in T 1 (97%) than in T 2 (56%). Both treatments were able to control the occurrence of the luminous bacterium Vibrio harveyi.
A feeding trial was conducted to evaluate the influence of dietary supplementation of Undaria pinnatifida fucoidan on growth performance and immunological response of juvenile Marsupenaeus japonicus. Four semipurified diets supplemented with graded levels of fucoidan (0.0, 100, 500, and 1000 mg/kg diet) were fed to juvenile shrimp for 8 wk. Each diet was fed to three replicate groups of shrimp. At the end of the feeding trial, enhanced growth performance was generally observed in shrimp fed the fucoidan‐supplemented diets when compared with the shrimp fed the control diet. Significantly higher weight gains, specific growth rates, protein retentions, and lower feed conversion ratios were observed in treatment groups fed the 500 and 1000 mg/kg dietary fucoidan supplementation when compared with the treatment groups receiving 100 mg/kg fucoidan supplementation and the control diet. Total hemocyte counts, phenol oxidase activity, and serum antibacterial activity were also significantly enhanced in shrimp fed diets supplemented with 500 and 1000 mg/kg fucoidan supplementation. These results suggest that U. pinnatifida fucoidan at a dose of 500 mg/kg diet could be used as an immunostimulant and a growth‐promoting dietary supplement for juvenile M. japonicus.
A new and emerging disease is threatening the shrimp industry, a bacterial disease which contains a highly pathogenic plasmid, creating a deadly toxin that causes high mortality in shrimps. The disease has been identified as acute hepatopancreatic necrosis disease (AHPND) or commonly known as early mortality syndrome (EMS). To help the efforts of sustaining the shrimp industry, the study focused on detecting Vibrio parahaemolyticus causing AHPND/EMS affecting Penaeus vannamei (Boone, 1931) (Pacific white shrimp) and Penaeus monodon (Fabricius 1798) (Black Tiger shrimp) in different locations in the Philippines. The presence of the disease was determined by microbiological methods and polymerase chain reaction (PCR) and was confirmed by the histopathology of the hepatopancreas of infected shrimp. Results show that the prevalence of the pathogenic strain of V. parahaemolyticus from the shrimps collected were 33% in Luzon, 21% in Visayas and 5% in Mindanao. The study presents the first record of AHPND/EMS in the country. The detection of this newly emerging disease in the shrimp industry is very crucial as it is the first step in identifying affected sites towards strategizing ways to combat the disease.
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