Assessment of Invasive Aquatic Weeds and its Effect on Fishery and other Aquatic Biota in Lake Tana, Amhara Region, Ethiopia (original) (raw)

The study was conducted from July 2014 to December 2017 in Lake Tana. Sampling sites chosen from Fogera, Libokemkem, Dembia, Bahirdarzuria and Takusa Woredas and purposive sampling sites were selected from each Woreda based on invasive weed infested areas. Plant sample was collected from infested areas using quadrant and different parameters were recorded using sensitive balance and tape meter. Dissolved oxygen (DO), pH, specific conductance (K 25), total dissolved solids (TDS), salinity (sal) and temperature (T) were measured in situ using YSI 556 multi-probe system. Measurements of ammonia (NH 3-N), phosphate (PO 4-P), nitrate (NO 3-N) and total hardness were carried out using a portable water analysis kit (Wagtech International, Palintest transmittance display photometer 5000). Water samples were collected from each sampling station up to a depth of 1m using a bucket of known volume. Zooplankton and phytoplankton samples were collected by 80 µm and 50 µm mesh net filtering device. Identification and enumeration of invasive weeds and planktons was made using standard procedures. As a result Water hyacinth, Azola, Potamogeton foliosus and water lettuce were investigated. In the case of water hyacinth hundred four plants/m 2 and 8.22 ± 0.45 kg fresh weight/ m 2 which equals to 82.16 tons/ha fresh weight could be harvested during the dry season of a year. But, 583 plants/m 2 (27.0 ± 0.61 kg fresh weight/m 2) which equals 270 tons/ha fresh weight could be harvested during the wet season of a year. The present assessment also noted that no major management strategy had been employed in the infested water body areas, despite many efforts had been applied by the community and the government. Water hyacinth (Eichhornia crassipes) is widely recognized as the world's worst aquatic weed. Originally exported from its native Amazonian basin because of its attractive flowers, the species rapidly established and spread throughout tropical, subtropical and warm temperate regions of the world [1]. It was indicated that this weed forms a dense impenetrable mats across water surface, limiting access by man, animals and machinery. Moreover, navigation and fishing are obstructed, and hydropower, irrigation as well as drainage systems become blocked. The weed was first introduced into Africa through Egypt sometimes between 1879 and 1882 (Friend, 1989). It has been recognized as the most damaging aquatic weed in Ethiopia since its first presence in 1965 [2,3]. It has been recognized its presence in lake Tana in 2011 [4]. Even though several efforts has been made by different parties, its expansion increased year after year. Therefore, there is a need to study some of its biology, impact on water quality, biota and current management options.