الفهرس 
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Abstract
Because of the sever economic and public health problems caused by harmful algal blooms, many studies have begun to concentrate on the control of undesired algal growth .This study was carried out at central laboratory for aquaculture research, Abbassa , Abu- Hammad, Sharkia. This study included two experiments. First one: pre test study that carried out in 3m3 concrete ponds to determine the optimum concentration of both aluminum sulfate and tannic acid that most effective for reduction and/or treating of harmful algal blooms for fourteen day. Second one: practical treating for the selected doses for removing and/or for reducing the harmful algal blooms from the earthen ponds stocked with fish fries for fourteen days. This experiment aimed to investigate the optimal doses of aluminum sulfate and tannic acid that might be suitable for treating harmful algal blooms on commercial ranges in earthen fish ponds. The results obtained from this study may be summarized as follows: A-first experiment:
(1) Determination of alum dose:
All the water quality parameters were within the acceptable ranges for fish growth. Also, the fish groups treated with all doses showed no significant differences with control ones. No significant difference in between the dose of 10 and 15 mg/l with small variation in their values recorded.
(2) Determination of tannic acid dose:
All the water quality parameters were within the acceptable ranges for fish growth. Also, the fish groups treated with all doses showed no significant differences with control ones. No significant differences between the concentration of 1.5 and 2mg/l.
B-second experiment:
Phytoplankton estimation:
Concerning the phytoplankton classes, it is clear that Cyanophyceae are the most dominant group of phytoplankton standing crop. Concerning the phytoplankton species it is clear that Anabaena are the most dominant species of phytoplankton standing crop. The highest PI of Anabaena was 99.7% for fish ponds treated with tannic acid at 14th day while, the lowest PI was 29.2% for the control ponds at 3rd day.
Zooplankton estimation:
Concerning alum treated ponds, the highest counts are observed in 7th day (236.6 organism/l )then is followed by pronounced decrease during 10th day (80 org/l) and then decrease during 14th day (30 org/l), while concerning tannic acid treated ponds the highest counts are observed in 5th day (131.6organism/l ) then is followed by a decrease during 7th day (118 org/l) , while concerning control ponds at 7th day the total counts of zooplankton increased up to 71.5 then followed by a pronounced decrease during 10th day (44.8 org/l) and then increase during 14th day (81.6 org/l).
Total bacterial count (T.B.C):
There were a significant difference between tannic acid treated ponds and untreated ponds after 7days, the no of T.B.C decreased after the addition of tannic acid. While, its count increased after 7th day in case of alum treated ponds and non-treated ponds (control).
Physico-chemical parameters of water:
Temperature:
The lowest water temperature (24.6 ± 0.16 °C) is recorded in tannic acid treatment during zero days, while the highest (26.5 ± 0.00C) is recorded in tannic acid treatment during 14th day.
Dissolved oxygen (DO):
The lowest concentrations are 4.7 ± 0.252 mg/l in tannic acid at 14th day and the highest concentrations 9.7 ± 0.057 mg/l in control at zero days respectively.
Secchi disc (SD) visibility:
The lowest Secchi disc value was (8.16 ± 0.6 cm) in control ponds at zero day, while the highest one (24.0 ± 4.509 cm) was in pond treated with alum at the14th day.
Hydrogen ion concentration:
The PH values within treated ponds and control ponds during 3rd, 5th, 7th, 10th and 14th were significantly decreased from the start to the end of treatment with both of alum and tannic acid over the control ponds. PH values ranged from8.8±0.06 at 14th day in tannic acid to 9.38±0.008 at zero day of control ponds.
Water conductivity:
The highest value (1.333 ± 0.163 µmhos) was recorded in alum treated ponds at zero days, while the lowest one (0.413 ± 0.037 µmhos) was recorded in the same treatment but at the 3rd day.
Total dissolved solids:
Total dissolved solids values for alum treated, tannic acid treated and control ponds were (0.606±0.011, 0.814±0.085and 0.539±0.19);(0.392±0.02, 0.645±0.182 and 0.537±0.114); (0.339±0.014, 0.417±0.075 and 0.559±0.115); (0.457±0.04, 0.441±0.04 and 0.585±0.12); (0.443±0.041, 0.456±0.098 and 0.502±0.082) and (0.442±0.041, 0.529±0.081 and 0.496±0.073) g/ l during zero, 3rd, 5th, 7th, 10th and 14th day respectively.
Total hardness:
The highest and lowest were 275.333 ± 2.667 and 196 ± 31.005 mg/l as CaCO3 recorded in alum treated ponds and control ponds at 14th and 3rd day, respectively at 14th day.
Total alkalinity:
The lowest value of total alkalinity (261.667 ± 11.667 mg/l as CaCO3) is recorded in control ponds during zero day, while the highest value (373.333 ± 1.667 mg/l as CaCO3) is recorded in alum and tannic acid treated ponds, respectively.
Orthophosphate:
The highest concentration of OP (0.201 ± 0.008 mg/l) was in tannic acid treated pond during 10th day, while the lowest concentration of OP was (0.00± 0.00mg/l) in alum treated ponds during both of 3rd and 5th day of treating.
Total phosphorus:
The highest values were at the start of experiment 1.437±0.170, 1.371±0.070 and 1.528±0.160 mg/l for alum, tannic acid and control ponds respectively, while the lowest TP values in alum was 0.235±0.018 at 7th day whenever, the lowest values of tannic acid and control 0.229±0.043 and 0.4150.010 at the 14th day of treating respectively.
Chlorophyll “a”:
The highest chlorophyll ”a” concentration (1118.633 ± 153.878 µg/l) was recorded in control ponds at zero day while; the lowest concentration (55.3±13.0 µg/l) was recorded in tannic acid treated ponds at 14th day.
Nitrate:
The maximum Water-nitrate concentration was 0.717±0.0.042 mg/l in alum treated at the 14th day while the minimum values were 0.018 ± 0.005 mg/l in control ponds at 3rd day. All treated ponds trend to increase in nitrate values with time of study.
Nitrite:
Values of nitrite was ranged 0.018±0.002 to 0.120±0.008 mg/l and 0.022±0.002 to 0.089±0.049 mg/l for alum and tannic at 14th and zero day, respectively. Meanwhile, in control the highest value was recorded in 14th day and the lowest one was in 3rd day.
Total ammonia:
The lowest value of total ammonia (0.167±0.089 mg/l) is recorded in tannic treated ponds at zero days, while the highest value was (2.033 ± 0.088 mg/l) in tannic acid treated ponds during 14th day.
Un-ionized ammonia:
The highest concentration of un-ionized ammonia (0.695 ± 0.03 mg/l) is recorded in tannic acid treated ponds during 10th day, while the lowest concentration (0.073 ± 0.009 mg/l) is recorded in the same treated ponds but at zero days before application of tannic acid.
Recommendation:
According to the obtained results the following aspects could be recommended
1- 10 mg / l (alum) and 1.5mg /l (tannic acid) could be considered as the optimum concentration for treating Anabaena blooms in fish ponds.
2- Sediment layer of ponds treated with aluminum sulfate should be removed.