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.

Seasonal growth of five commercially important fishes at Sofala Bank, Mozambique

An analysis of growth of scad and mackerels on Sofala Bank, Mozambique, was performed using data collected from commercial vessels during the year 1986-87, using the "Compleat Elefan" software package. Updated estimates of growth parameters of Decapterus russelli, D. macrosoma (Carangidae), and Rastrelliger kanagurta (Scombridae) were obtained which take seasonal growth oscillations into account. Preliminary growth parameter estimates are also presented for Selar crumenophthalmus (Carangidae) and Saurida undosquamis (Synodontidae).

Watermasses, currents and tides at the Sofala Bank, November 1987

The southern part of the Sofala Bank (in Mozambique) was investigated. A net of closely spaced hydrographic stations were obtained and a current meter mooring consisting of two current meters and a bottom pressure recorder was deployed. High salinity shelf water was observed near shore with a maximum salinity above 36.6 ppt. Both average and tidal currents are discussed. The mean currents are steered by the continental slop and seem to be influenced by the wind. The tides have strong semidiurnal components, with a major axis of 53 cm/s perpendicular to the coast at 60m depth. The possibility that the tides may transport passive drifters with a diurnal vertical migration pattern up to a few kilometers a day is considered.

Reproduction, age and growth of the Russell's scad, Decapterus russellii (Rüppel, 1828)(Carangidae) from Sofala Bank, Mozambique

Age, growth and reproduction of D. russellii were studied. Most of the material used was caught by the commercial fishing fleet, operating in the Sofala Bank (Mozambique) area. A total of 68,000 fish were examined during the period 1979-1981. There were 2 main spawning periods each year, one in February-March and another in August-September. The sex ratio was about 1:1. Ageing was carried out using primary growth rings in the otoliths and analysis of size-frequency distributions. The parameters of the von Bertalanffy's growth equation were determined. Males and females grew at the same rate.

Report on the oceanographic investigations carried out at the Sofala Bank by the Soviet trawler "Sevastopolsky rybak" in September-December 1982

In September-December 1982 a fisheries research cruise was carried out at the Sofala Bank by the SRTM "Sevastopolsky Rybak". Oceanographic investigations have been conducted in association with the fisheries research. Three coverages were made of the Sofala Bank each lasting for slightly less than three weeks. This will allow for three descriptions of the oceanographic conditions in the area, with some reference being made to variability. This paper is just a preliminary report of those investigations.

Hydrology and fish distribution at the Sofala Bank (Mozambique)

A brief review is made of the hydrologic conditions at the Sofala Bank, mainly based on the research data obtained from 1978 to 1982. A description is attempted of the circulation pattern and the distribution of water masses in the area, four hydrologic regimes being identified. These are compared with the distributions of different pelagic and demersal fish species. A tendency is found for different groups of species to prefer different hydrologic regimes.

A preliminary assessment of the scad and mackerel stocks at Sofala Bank, Mozambique

Scads (Decapterus russellii, D. macrosoma, Selar crumenophthalmus), Indian mackerel (Rastrelliger kanagurta) and horse mackerel (Trachurus trachurus) are the main pelagic species caught in a bottom trawl fishery at Sofala Bank and at Boa Paz. Information on catch and effort is presented together with available data on distribution, spawning, size at first maturity, growth, mortality and biomass of the species. As the present catch and fishing mortality are low compared to the estimates of biomass and total mortality it is concluded that the fishery may be expanded further in the future.

A preliminary study on the cuttlefish catches from the Wadge Bank trawler fishery

Although much work has been done on the evaluation of the Wadge Bank fishery data, no detailed study has been made in the past on the analysis of cuttlefish catches. In this paper an attempt has been made to analyse this data in order to gather a preliminary knowledge of seasonal and annual variation in the availability, distribution by depth and catches in relation to the time of the day.

Cryopreservation of sperm of common carp, Cyprinus carpio and silver barb, Barbonymus gonionotus for genetically improved seed production

Experiments were conducted to develop and standardize the protocols for cryopreservation of sperm of common carp, Cyprinus carpio and also for using the cryopreserved sperm for fertilization of eggs. Nine extender solutions as Alsever's solution, kurokura-1, kurokura-2, urea egg-yolk, egg-yolk citrate, 0.6% glucose, 0.9% NaCl, Ma and Mb, and five cryoprotectants namely ethanol, methanol, dimethylsulfoxide (DMSO), dimethylamine (DMA) and glycerol were tested. The cryoprotectants were mixed at 10% concentration of the extenders (v/v) to make the cryodiluents. Milt and cryodiluents were mixed at a ratio of 1:9 for Alsever's solution, kurokura-1, kurokura-2, 0.6% glucose and 0.9% NaCl, 1:4 for urea egg-yolk, egg-yolk citrate, Ma and Mb. Among the cryodiluents Alsever's solution mixed with either ethanol or methanol was found to be suitable and it produced more than 90% and 80% spermatozoan motility at equilibrium and post-thaw periods, respectively. Kurokura-1 and kurokura-2 when mixed with the same cryoprotectants showed good spermatozoan motility at equilibrium period (80-90%) but the motility was reduced (30-55%) at post-thaw state. Other extenders did not produce acceptable sperm-motility and in some cases the frozen milt became clotted. Different dilution ratios (1:1, 1:2, 1:4, 1:5, 1:7, 1:9, 1:12, 1:15, 1:20) were formulated for obtaining a suitable milt dilution, the dilution ratio of 1: 9 (milt : cryodiluent) demonstrated the highest post-thaw spermatozoan motility (80%) in Alserver's solution. The optimum concentration of cryoprotectants in the cryodiluents was determined, 10% concentration level was found to be effective to produce the highest number of spermatozoan motility in comparison to the other concentrations (5%, 15%, 20% 30%). Sperm preserved with the cryodiluent Alsever's solution along with either methanol or ethanol was found to be effective to fertilize eggs and produce hatchlings. The hatching rates ranged between 1.48% and 14.76%, compare to control. The fish produced through use of cryopreserved sperm and normal sperm were found to grow well and no significant (P<0.05) growth difference was observed between them. In case of silver barb, Barbonymus gonionotus, sperm tested against six extenders such as egg-yolk citrate, urea-egg-yolk, kurokura-1, kurokura-2, 0.9% NaCl and modified fish ringer (MFR) solution. Cryoprotectants used were the same as those of C. carpio. Milt was diluted with the cryodiluent at a ratio of 1:4 for egg-yolk citrate and urea-egg-yolk, 1:5 for kurokura-1 and 1:9 for 0.9% NaCl, MFR and kurokura-2. The cryoprotectant concentration was maintained at 10% of the extender (v/v) in all the cases. Among the extenders, egg-yolk citrate and urea-egg-yolk mixed with 10% DMSO, methanol and ethanol produced 50% post-thaw spermatozoan motility, whereas DMA and glycerol provided only 10% motility. Trials on milt dilution ratio and cryoprotectant concentration are being conducted. Fertilization trials are also underway.

Breeding biology and monosex male seed production of Genetically Improved Farmed Tilapia (GIFT) strain of Oreochromis niloticus L. in Bangladesh

A study on the breeding biology of the GIFT strain of Nile tilapia, Oreochromis niloticus, was conducted for a period of five months. The sex ratio of the parent individuals was optimized for performance in spawn production, where the best results were obtained with a sex ratio of female to male of 4:1 compared to those of 3:1 and 2:1. The diameter of eggs obtained from the GIFT stock had major and minor axes of 2.19±0.09 and 1.72±0.07 mm, respectively, with no significant differences between the treatments. The average number of eggs produced was 392±22 per female, with fertilization and hatching rates ranging between 94-96% and 85-88%, respectively. No significant variation was observed between the treatments. Breeding frequencies per female in the three treatment groups ranged between 10-40 days and the highest value was obtained at a female to male sex ratio of 4: l. In an other experiment, l7 aMethyltestosterone (MT) was applied orally to the fry at their first feeding stage with treatments- 1, 2, 3 and 4 at the dosage of 100, 80, 60 and 40 mg/kg feed respectively, for the period of 28 days. The mean percentage of males obtained in treatments, 1, 2, 3 and 4 were 98, 97, 95 and 68, respectively. Treatments-1, 2 and 3 did not differ significantly (P>0.05) from each other but treatment 4 showed significant variation (P<0.05) from other treatments. The results showed that MT-100, 80 and 60 mg/kg feed administered for 28 days produced close to cent percent male population of the GIFT strains in aquaria.

Status of fish broodstock management and seed production in Bangladesh

The study was conducted with the broad objectives to assess the existing situation of broodstock management and fish seed production in private fish seed farms in Bangladesh. The data were collected from 100 private hatcheries and 40 nurseries in seven upazilas under four districts. There was no shed in forty hatcheries and the owners faced many problems. Brood fish ponds were found suitable for rearing brood fish. About 66% of the hatchery owners collected brood fish from their own ponds and ponds of neighboring areas. Activities like pond preparation; manuring and supplementary feeding were done properly but stocking density of brood fish in 76% of the hatcheries was 3,000-7,000 kg/ha. Infection of argulosis was found in brood fish of 87% of the hatcheries. About 67% of the hatchery owners practiced inter-species crossing. Major problems faced by the hatchery owners were argulosis of brood fish, unavailability of pure brood stock, inadequate brood fish pond. The hatchery owners were found interested to find out the preventive measures of argulosis, develop pure brood stock of indigenous carp and import pure strain of exotic carp. According to the nursery operators, they cultivated hybrid fry because of high demand, rapid growth and good taste. Problems of using hatchery spawn as mentioned by the nursery operators were inbreeding, under sized and aged brood stock, stunted growth, physical deformities and high mortality of spawn due to unknown causes.

Investment in fish seed multiplication farms in Bangladesh: Evidences of an attractive business

This study mainly evaluated the profitability of Fish Seed Multiplication Farms (FSMFs) having hatchery, nursery and hatchery-cum-nursery located in the districts of Jessore, Jhenidah and Narail in Bangladesh. The general findings of the study were that the investment in FSMFs with hatchery, nursery and hatchery-cum-nursery was highly profitable business. The results clearly indicated that the investment on hatchery was the most profitable than those of nursery and hatchery-cum-nursery operations from the viewpoints of individual investors. The results of sensitivity analysis suggested that the investment in nursery farm was a risky business with 20 per cent increase in operation and management as well was production costs or 20 per cent reduction in benefits if other things remaining the same. It was also evident from the study that the investors of FSMFs had currently been facing some crucial problems, which among others are: problems of inbreeding, shortage of brood fish, incidence of diseases, unavailability of certain inputs and lack of credit.

Institutional support for freshwater aquaculture development: a study of Mirzapur district of Uttar Pradesh, India

The aquaculture sector has been playing an increasingly dominating role in Indian fisheries scenario since the last two and half decades. Introduction of induced breeding and composite fish culture (CFC) technologies has changed the freshwater aquaculture sector in India. Institutional support has been one of the most crucial aspects in all fisheries development programs, more so in the Indian context where most of fish farmers are socially and economically weak. The innovation of CFC technology in freshwater aquaculture sector in the early seventies generated the need for adequate and effective institutional support to farmers. Under the freshwater aquaculture development program, the Fish Farmers Development Agencies (FFDA) have been established at district level to provide technical and extension support to the farming community besides arranging ponds on lease and supply of seeds. In addition to above, FFDAs are also expected to arrange loans from banks and provide subsidies. Thus, FFDAs are meant to provide institutional support to fish farming community in the country. In view of the above, an effort was made to study the adequacy and effectiveness of institutional support provided by the FFDA, Mirzapur for the development of aquaculture in Mirzapur district of Uttar Pradesh {U.P.), India. Study reveals that leasing of ponds for fish farming has been favourable to economically weaker sections of societies while bank loan accessibility is more for those having relatively higher economic status. Though the FFDA, Mirzapur performed well in providing training to potential fish farmers and creating awareness about fish farming, its effectiveness could not be equally seen in seed supply.

Seed production and culture techniques of Genetically Improved Farmed Tilapia (GIFT) in brackishwater environment

Effects of different levels of salinity on survival, growth and gonadal development of Genetically Improved Farmed Tilapia (GIFT) were studied under laboratory conditions in glass aquarium, for a period of ten weeks. The initial individual size of the GIFT was 20.23±4.45 and the salinity levels tested were 0, 5, 10, 15 and 20 ppt. The highest survival of 87.5% was found in 0 ppt and the lowest 60.5% in 20 ppt. Though the survival decreased progressively with increased salinity, there were no significant differences (P>0.05) among 0, 5, and 10 ppt. Similar to what has been observed in survival, the specific growth rate (SGR %/day) also decreased as of 1.30, 1.24, 1.08, 0.90 and 0.71, respectively, with the increased salinity of 0, 5, 10, 15 and 20 ppt. The gonadal development was highest in 0 ppt with a GSI value of 3.75 and lowest of 2.01 in 20 ppt. In the second experiment, gonadal development and seed production performance of GIFT in brackishwater condition were investigated for a period of three months. Each of the three fine meshed hapas of 20 square meters made from nylon net was placed in a freshwater (0 ppt) and in a brackish water (10-15 ppt) pond of the Brackishwater Station (BS). GIFT of 65 g average weight from a single cohort were stocked into three hapas at a rate of 2 per m. The male vs female ratio was 1:3. The development of gonad was faster with the higher gonadosomatic index (GSI %) of 3.85 % in freshwater condition than that of 2.73 % in brackish water. Within three months of the study period, a total of 70,510 and 44,250 GIFT fry were produced respectively, in freshwater and brackishwater conditions. Finally under third experiment, a participatory on-farm trial was carried out to evaluate the production performance of GIFT in monoculture and in polyculture with silver barb in coastal freshwater pond conditions. Nine ponds were selected for three treatment combinations of GIFT monoculture (T1), GIFT and silver barb polyculture (T2), and silver barb monoculture (T3). The ponds have been stocked in April, 05 at a density of 25,000 fry per ha. Fishes were fed with rice bran at the rate of 6% bw per day. In one month culture period, GIFT attained an average weight of 16.27 g in monoculture and 17.23 g in polyculture, against an average stocking weight of 0.37 g. Silver barb reached an average weight of 16.62 g in polyculture with GIFT and 10.01 g in monoculture, against an average stocking weight of 3.79 g.