Japanese threadfin bream Nemipterus japonicus（Bloch, 1791） is among the most abundant and commercially important species in Pakistan. From the coast of Pakistan, four demersal trawl surveys in October–November 2009...Japanese threadfin bream Nemipterus japonicus（Bloch, 1791） is among the most abundant and commercially important species in Pakistan. From the coast of Pakistan, four demersal trawl surveys in October–November 2009 and May–June, August, October and November in 2010 were carried out. The purpose of this study is to estimate the population dynamics and status of the stock of the N. japonicus from Pakistani waters based on the research trawl surveys from the research area. The data consist of n=784 length-weight pairs and n=7 530 length frequency with the maximum length and weight of 29 cm and 358 g respectively. The length frequency data were analyzed using ELEFAN method in FiSAT computer package. The parameters of length and weight relationship were b=2.778, a=0.032 and R2=0.973. The estimated von Bertalanffy growth function parameters were L∞=30.45 cm, K=0.270 year-1. Based on length-converted catch curve analysis the total mortality（Z） during this study was estimated at 0.960 year-1. The natural mortality coefficient（M） was 0.74 year-1 using Pauly＇s equation（the annual average sea surface temperature was 27°C）, therefore, the fishing mortality coefficients（F） were 0.22 year-1. The yield per recruit analysis indicated that when tc was 2, Fmax was estimated at 1.2 and F0.1 at 1.1. When tc was 1, Fmax was estimated at 0.95 and F0.1 at 0.8. Because current age at first capture is about 1 year and Fcurrent was 0.22, Fcurrent is smaller than F0.1 and Fmax, which indicated that the fishery is about in a safe condition. When using Gulland（1971） biological reference point, Fopt was equals to M（0.74）. The current fishing mortality rate of 0.22 was smaller than the target biological reference point.展开更多
In order to plan a management programme for ensuring maximum production of fish in Cross River, impacted downstream changes in the fish community structure by effluents from wood processing industry, six years after e...In order to plan a management programme for ensuring maximum production of fish in Cross River, impacted downstream changes in the fish community structure by effluents from wood processing industry, six years after establishment, was examined. Monthly samples were collected between January and December each year from 2000 to 2006 in three reaches (Upriver: I, Mid-river: II and Downriver: III) along the length of Cross River. Representatives of the fish families Osteoglossidae (i.e. Heterotis niloticus), Cichlidae (Tilapia melonopleura) and Characidae (Bryocinus nurse), Clupeidae (Cynothrissa sp), Mormyridae (Mormyrus deliciosus), Clariidae (Clarias gariepinus), Bagridae (Bagrus bayad) and Cyprinidae (Barbus occidentalis) were found to have declined in their importance compared to pre-industry period. On the other hand, Bagridae (Chrysichthys nigrodigitatus), Cichlidaae (Orechromis niloticus), Claridae (Clarias anguillaris) and Mochokidae (Synodontis clarias) have currently emerged as most important. Estimated value of growth coefficient (b) of the length-weight relationship changed from isometry (b approx. = 3) to negative allometry (b ≤ 3), condition factor values decreased from range between 0.53 and 1.30 to range between 0.22 and 0.62. Main feeding groups of fish;planktivores, carnivores and insectivores declined in numbers while omnivores and detritivores increased, resulting in dominance of benthic and semi-pelagic omnivores. Values of fecundity distribution varied from 56,012 ± 5234 eggs, mode 12,500 and median 58,345 to mean value 23,122 ± 232 eggs, mode 2500 and median 20,349, egg size from mean value;1.82 ± 0.07 mm, mode 2.2, and median;1.8 to values of 0.8 ± 0.04 mm, mode;1.3 and median 1.1 and Gonadosomatic index from 20.5 ± 3.2, mode 19.1 ± 2.2 and median 21.4 to values of 12.4 ± 2.3, mode 4.5 and median 9.5 respectively. Three species found to have appeared in the river were Tilapia monody, Chrysichthys maurus and Synodontis violaceus. The appearance of these species and disappearance of 36展开更多
基金The special research fund of Ocean University of China under contract No.201022001
文摘Japanese threadfin bream Nemipterus japonicus（Bloch, 1791） is among the most abundant and commercially important species in Pakistan. From the coast of Pakistan, four demersal trawl surveys in October–November 2009 and May–June, August, October and November in 2010 were carried out. The purpose of this study is to estimate the population dynamics and status of the stock of the N. japonicus from Pakistani waters based on the research trawl surveys from the research area. The data consist of n=784 length-weight pairs and n=7 530 length frequency with the maximum length and weight of 29 cm and 358 g respectively. The length frequency data were analyzed using ELEFAN method in FiSAT computer package. The parameters of length and weight relationship were b=2.778, a=0.032 and R2=0.973. The estimated von Bertalanffy growth function parameters were L∞=30.45 cm, K=0.270 year-1. Based on length-converted catch curve analysis the total mortality（Z） during this study was estimated at 0.960 year-1. The natural mortality coefficient（M） was 0.74 year-1 using Pauly＇s equation（the annual average sea surface temperature was 27°C）, therefore, the fishing mortality coefficients（F） were 0.22 year-1. The yield per recruit analysis indicated that when tc was 2, Fmax was estimated at 1.2 and F0.1 at 1.1. When tc was 1, Fmax was estimated at 0.95 and F0.1 at 0.8. Because current age at first capture is about 1 year and Fcurrent was 0.22, Fcurrent is smaller than F0.1 and Fmax, which indicated that the fishery is about in a safe condition. When using Gulland（1971） biological reference point, Fopt was equals to M（0.74）. The current fishing mortality rate of 0.22 was smaller than the target biological reference point.
文摘In order to plan a management programme for ensuring maximum production of fish in Cross River, impacted downstream changes in the fish community structure by effluents from wood processing industry, six years after establishment, was examined. Monthly samples were collected between January and December each year from 2000 to 2006 in three reaches (Upriver: I, Mid-river: II and Downriver: III) along the length of Cross River. Representatives of the fish families Osteoglossidae (i.e. Heterotis niloticus), Cichlidae (Tilapia melonopleura) and Characidae (Bryocinus nurse), Clupeidae (Cynothrissa sp), Mormyridae (Mormyrus deliciosus), Clariidae (Clarias gariepinus), Bagridae (Bagrus bayad) and Cyprinidae (Barbus occidentalis) were found to have declined in their importance compared to pre-industry period. On the other hand, Bagridae (Chrysichthys nigrodigitatus), Cichlidaae (Orechromis niloticus), Claridae (Clarias anguillaris) and Mochokidae (Synodontis clarias) have currently emerged as most important. Estimated value of growth coefficient (b) of the length-weight relationship changed from isometry (b approx. = 3) to negative allometry (b ≤ 3), condition factor values decreased from range between 0.53 and 1.30 to range between 0.22 and 0.62. Main feeding groups of fish;planktivores, carnivores and insectivores declined in numbers while omnivores and detritivores increased, resulting in dominance of benthic and semi-pelagic omnivores. Values of fecundity distribution varied from 56,012 ± 5234 eggs, mode 12,500 and median 58,345 to mean value 23,122 ± 232 eggs, mode 2500 and median 20,349, egg size from mean value;1.82 ± 0.07 mm, mode 2.2, and median;1.8 to values of 0.8 ± 0.04 mm, mode;1.3 and median 1.1 and Gonadosomatic index from 20.5 ± 3.2, mode 19.1 ± 2.2 and median 21.4 to values of 12.4 ± 2.3, mode 4.5 and median 9.5 respectively. Three species found to have appeared in the river were Tilapia monody, Chrysichthys maurus and Synodontis violaceus. The appearance of these species and disappearance of 36
