Population dynamics of the ribbon fish, Lepturacanthus savala (Cuvier 1829) from the north-eastern part of the Bay of Bengal

Population parameters of Lepturacanthus savala from the trawl catches in the north-eastern part of the Bay of Bengal, Bangladesh were investigated based on length frequency data, using complete ELEFAN computer program. The asymptotic length (Lα) and growth constant (K) were estimated to be 106.50 cm (total length) and 0.80/year respectively. Based on these growth parameters, the total mortality (Z) was estimated to be 1.89. The estimated values for natural mortality (M) and fishing mortality (F) were 1.08 and 0.81 respectively. The estimated value for the exploitation rate (E) using the length converted catch curve was 0.43. The recruitment pattern showed two peaks per year. The estimated sizes of L. savala at 25, 50 and 75% probabilities of capture were 57.49, 60.39 and 63.28 cm respectively. The estimated length weight relationship for combined sex was W=0.00093 TL(super)2.97

Stock dynamics of horse mackerel, megalaspis cordyla (Linnaeus) along northwest coast of India

The stock dynamics of horse mackerel, Megalaspis cordyla, along the northwest coast of India has been studied using length frequency data recorded from commercial landings and trawl catches of research-cum-training vessel M.F.V. Saraswati. The growth parameters for this species has been estimated to be L∞=54 cm and K=0.49 per annum. The natural and fishing mortality for the stock have been worked out to be 0.93 and 0.91 per annum respectively. The study indicated that the stock is fished at a safer fishing mortality level F sub(0.1), lower than F sub(msy) level.

Population dynamics of penaeid prawn Penaeus merguiensis off Mumbai coast

Stock dynamics of Penaeus merguiensis was studied using length composition data collected separately for males and females during the period 1995-1998, at New Ferry Warf landing, centre in Greater Mumbai. Food and feeding, sex ratio, fecundity and length-weight relationships were worked out on a representative sub-sample. Asymptotic length (Loo) and growth coefficient (K) were estimated to be 220 mm and 1.80 per annum respectively for males. These parameters were respectively 281 mm and 1. 72 per annum in the case of females. The instantaneous rate of total mortality coefficient (Z) was found to be 9.79 and 7.44 per annum for males and females respectively. The annual natural mortality coefficient (M) was estimated to be 2.80 for males and 2.60 for females. As the exploitation ratio exceeded 0.5 in the case of both the males and females, the study suggests the necessity for reduction in fishing pressure in order to achieve Maximum Sustainable Yield (MSY).

Population dynamics of Penaeus indicus at Sofala Bank, Mozambique: a preliminary study

Length-based methods are used to estimate growth and mortalities of Penaeus indicus at Sofala Bank in Mozambique. This Penaeid shrimp is one of the most important species in the fishery as it constitutes 45% of the catches and has a great influence in their trend. First estimates of growth parameters for this species in Mozambique are presented and a comparison of the derived mortalities with the previous estimates is made.

Preliminary investigations on the population dynamics of Otolithes ruber (Sciaenidae) on Sofala Bank, Mozambique

Catch length-frequency data of Otolithes ruber (Schneider, 1801) obtained from the "Projecto de Pesca Experimental da RDA" on Sofala Bank, Mozambique, in 1987 were used to estimate growth parameters, mortalities and exploitation rates. The yield-and biomass-per-recruit analyses based thereon suggest that the stock is overfished.

Population dynamics of two jewfishes Jhonius argentatus and Johnieops vogleri) in the coastal waters of Bay of Bengal, Bangladesh

Population parameters of Jhonius argentatus and Johnieops vogleri in coastal waters of Bay of Bengal, Bangladesh were estimated by using FiSAT programme. The von Bertalanffy growth parameters, extreme length (cm) and growth constant K (year ·1) were found to be 46.50 and 0.59 for J. argentatus, and 33.50 and 0.85 for J.vogleri The Loc(cm) and Z/K estimates provided by Wetherall plot were 46.694 and 1.791 for J. argentatus, and 31.25 and 2.623 for J. vogleri. The annual rate of natural (M) and fishing mortality (F) were estimated as 1.12 and 0.78 for J. argentatus, and 1.56 and 1.28 for J. vogleri. Rate of exploitation (E) was estimated as 0.41 for J. argentatus and 0.45 for J. vogleri. About 80.04% of J. argentatus were found to be recruited during peak pulses (April-May) and 19.96% during lean pulses (October-November) and 85.75% J. vogleri during peak pulses (May-July) and 14.25% during lean pulses (September-October). The growth performance index(') was 3.11 for J. argentatus and 1.93 for J. vogleri. The total length and body weight relationship was found to be W = 0.0403 TL25723 for J. argentatus and W = 0.0907 TV3482 for J. vogleri.

Population dynamics of killifish Aphanius dispar (Ruppel) in Sandspit area off Karachi

Growth and mortality parameters of Aphanius dispar a cyprinoides generally observed in the catches of near shore area were estimated from the length frequency data collected from Sandspit area of Karachi, using LFSA. The von Bertalanffy growth parameters were estimated as Loo=71.73 mm & K=L35/yr for Male Aphanius dispar and Loo=70.66 & K=l.41 for female. Total Mortality coefficient (Z) was estimated using Length converted catch curve which is equal to 2.12/yr, for male and for female 2.19/yr. Natural mortality (M) was estimated by Pauly's empirical formula: M=l.64/yr (male) and 1.70/yr (female). The species also displayed two cohorts a year.

Seasonal dynamics of phytoplankton in relation to environmental factors in the Maheshkhali channel, Cox's Bazar, Bangladesh

In total 68 phytoplankton species were identified at the mouth of the Maheshkhali channel with the Bay of Bengal, among them 41 belong to Bacillariophyceae, 17 Dinophyceae, 7 Cyanophyceae and 3 to Chlorophyceae. The highest phytoplankton production was observed in November (578.0 x 105 cells/L) and the lowest in June (37.5 x 105 cells/L). Some hydrographic parameters e.g., surface water temperature, salinity and nutrients (N03-N and P04-P) were recorded and their relationship with the occurrence and abundance of phytoplankton population were also studied. Nutrient concentration was higher during the autumn months, when rain water provided the maximum outflow of rivers discharging into the channel. During the nutrient peak period, the total phytoplankton production was maximum. Bacillariophyceae was the dominant group of phytoplankton throughout the study period except in June and September, when Dinophyceae was dominant. Cyanophyceae was abundant in spring months when temperature began to rise.

Emigration dynamics of three species of penaeid prawn from backwaters and tidal ponds of Cochin, India

Emigration of three species of penaeid prawn from backwaters and tidal ponds were studied. Considerable diel, tidal, lunar and seasonal fluctuations were observed in emigration process, which was almost nocturnal. Rate of emigration and composition of emigrants varied with time of migration. Large pulses of emigration always coincided with spring tides with major peak during new moon. Seasonal variation was observed with peak emigration of Penaeus indicus during monsoon months and that of Metapenaeus dobsoni and Metapenaeus monoceros during pre-monsoon. Rate of emigration was relatively large from shallow tidal ponds. It correlated directly with the prevailing environmental conditions and juvenile density. Instantaneous rate of emigration was also large in seasonal ponds. The basic stimulus for emigration is the urge for sexual maturation. Coupled with it ecological changes in the habitat have been causing various patterns in migration.

Dynamics of parasite population and its histopathological and histophysiological effects in the stomach of a freshwater fish

The caryophyllaeid cestode Lytocestoides fossilis infects the freshwater catfish Heteropneustes fossilis. The study was conducted for two consecutive years (2004-06) to record the bio-statistical data of the parasite. The incidence, intensity, density and index of infection of the parasite have been recorded. The infection was more during June to September, moderate during February to May and low during October to January. The parasite brought about severe histopathological changes in the stomach of infected fish. The changes observed in the stomach of fish included structural damage of the villi, inflammation, and fibrosis associated with hyperplasia and metaplasia. The hypertrophy of mucous layer led to vacuolation and necrosis. Histochemical changes were noticed with enhanced carbohydrate, protein and lipid contents. The enhanced substrate content in the infected organ might be due to the disfunctioning of the digestive tract, which results in the accumulation of various metabolites. Mucus secretion was triggered as a protective interaction against parasitic invasion. The parasitic infection affects the general metabolic state of the host and as the result, the fish becomes sluggish and moribund.

Population dynamics of a cladoceran zooplankter, Daphnia magna, in two poultry-cum-fish (duck-fish and chicken-fish) integrated ponds

The population dynamics of Daphnia magna was studied in two integrated fish-cum-poultry ponds (duck-fish and chicken-fish). The seasonal changes in the population of D. magna were recorded. Peak population of the zooplankter was recorded in the month of January in both ponds. The birth rate (b), growth rate (r) and death rate {d) of D. magna were studied in field as well as in the laboratory. Three temperatures and three different food concentrations were selected for laboratory study. The maximum values of (b) and (r) were recorded during December-January in field. Under laboratory conditions, highest birth and death rate occurred at lowest temperature (15 °C). Both food and temperature were found to affect the population dynamics of the species; longest life span and maximum population were recorded at lowest temperature and maximum food concentration.

Ingression, abundance and settlement dynamics of Penaeid chrimp postlarvae in backwaters and adjacent tidal ponds in Cochin, India

Dynamics of penaeid postlarval ingression and settlement in the backwaters of Cochin were studied. Postlarval recruits were constituted by Metapenaeus dobsoni (70.8-78.4%), Penaeus indicus (17.5-24.6%), M. monoceros (3.8-4.6%) and P. monodon (0.3-0.4%). Their composition varied with location and season. Postlarval abundance and ingression were influenced by diel, tidal, lunar and seasonal factors. Ingression is mainly nocturnal in all species with nearly 84% of the activity during night hours. Abundance and ingression peaked up during high tides at night with major peaks coinciding with spring tides of full and new moon. It also followed a generalized seasonal pattern with two well-defined peaks for all species. It was pre-monsoon followed by post-monsoon for P. indicus and M. monoceros and post-monsoon followed by pre-monsoon for M. dobsoni. Sizes of the recruits were relatively small during pre-monsoon and post-monsoon and large during monsoon.

Population dynamics of Terapon jarbua (Forskal) in coastal area of Pakistani waters

Terapon jarbua is a widely distributed species in Pakistani inshore waters. It is well cherished by local coastal population. Present study is an attempt to determine some parameters of the population dynamics of the species in Pakistani waters. Analysis of data shows that the species attains asymptotic length (Loo) at 33.2 cm and have growth curve (K) of 0.62. Total mortality coefficient (Z) comes to 1. 67 per year, natural mortality coefficient (M) is estimated as 1.23 per year. The fishing mortality (F) is about 0.44 per year; whereas exploitation rate E=0.26.

Some major unsolved aspects of the dynamics of African fisheries as related to questions of rational development and management

Studies of fish and fisheries in Africa fall in to four phases: the period of fisheries expeditions, ecological investigations, the development phase, and the period of mechanized exploitation. There is need to establish the taxonomic status and ecology of the varied components of the potentially important Haplochromis in Lake Victoria. A comprehensive study of their bionomics and life history, population structure, natality, recruitment and mortality coefficients should be undertaken. Emphasis lo be laid on the study of the ecology, especially breeding behaviour of the economically important c1upeids (Stolothrissa tanganciae and Limnothrissa miodon), in Lake Tanganyika. A comprehensive investigation into the migratory and shoaling behaviour of the Lake Victoria Tilapia to be initiated. Pre-impoundment studies to be undertaken to assess effects of hydroelectric projects of fisheries. Studies on parasites of economically important fishes to be stepped up to assess pathological effects and the biological basis for their control. The role of predators, e.g., Hydrocyon, Lates and Micropterus salmoides in commercial fish populations should be evaluated, and the knowledge gaincd used to effectively manage the fisheries in favour of the more desirable fish stocks.