The effect of the introduction of Nile tilapia ( Oreochromis niloticus , L.) on small indigenous fish species (mola, Amblypharyngodon mola , Hamilton; chela, Chela cachius , Hamilton; punti, Puntius sophore , Hamilton)

This is the first controlled experiment to quantify the effect of introduced tilapia on indigenous species. This experiment was conducted in small earthen ponds (100 m 2 ) to assess the impact of mixed-sex or all-male Nile tilapia ( Oreochromis niloticus ) on small indigenous species (SIS) commonly found in south Asia, mola ( Amblypharyngodon mola ), chela ( Chela cachius ) and punti ( Puntius sophore ). Ponds were fertilized, then stocked with 0.56 fish m −2 of water surface area in the mixed-sex and all-male tilapia treatments and 0.42 fish m −2 in the treatment without tilapia. No additional nutritional inputs were applied after stocking. Treatments were: mixed-sex tilapia with SIS, mono-sex male tilapia with SIS and SIS without tilapia (control). All treatments were stocked with 14 fish per species. All species reproduced during the 21-month culture duration. The number of recruits varied by species, Tilapia reproduced in greater numbers than SIS. Tilapia numbers at harvest were the highest (451 ± 25/100 m 2 ) in the mixed-sex treatment compared with mola (221 ± 22/100 m 2 ), chela (94 ± 8/100 m 2 ) and punti (100 ± 7/100 m 2 ). The number of mola was higher (399 ± 33/100 m 2 ) in the all-male tilapia treatment. There was reduction in the number of mola and chela in the treatment containing mixed-sex tilapia. Gut content analysis combined with water sampling revealed that all fish species fed selectively. Significant interspecies dietary overlap was found between Nile tilapia and SIS and among SIS. Thus, there is potential for tilapia to compete with indigenous fish species when space and other resources are limiting, but a longer duration study with varying level of management is needed to determine how successfully tilapia competes with locally adapted SIS.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79201/1/j.1365-2109.2009.02372.x.pd

Production potential of greater duckweed Spirodela polyrhiza (L. Schleiden) and its biochemical composition evaluation

The culture technique of greater duckweed Spirodela polyrhiza (L. Schleiden) was standardized in outdoor tanks using three different manures: manure 1 - cattle manure, poultry droppings and mustard oil cake, manure 2 - urea, potash and triple superphosphate and manure 3 - cattle manure, urea, potash and triple superphosphate. Significantly (p   <  .05) higher production was recorded in manure 1 compared to others. Manure 1 was subsequently selected for pond culture. In ponds, the production of duckweed was 2020 ± 150 kg ha−1 month−1 dry weight basis. Protein content was significantly higher (p  <  .05) in duckweed cultured in manure 1. The amino acid profile study showed the presence of essential (37.4%), non-essential (58.2%) and free (4.5%) amino acids. Leucine, isoleucine and valine contributed 51.4% of total essential amino acids. Duckweed contained 7% lipid and α-linolenic acid (36–37%) was the major fatty acid. The study showed the nutritional value of duckweed as an animal feed ingredient

Managing Fisheries Resources in Kaptai Reservoir, Bangladesh

This paper examines the various challenges facing the development of fisheries resources in Kaptai reservoir, Bangladesh. The reservoir has undergone major changes in its catch composition since impoundment. Production records show a declining trend in the productivity of high-value fish. A host of managerial, socioeconomic and environmental factors are responsible for the underutilization of the reservoir's potential to provide high-value freshwater fish. These include deterioration of the natural breeding ground, environmental damage, poor implementation of regulations, inefficient fish farming technology and poor management practices. These constraints are discussed and possibilities for future improvements are suggested