A comparative assessment of the methods of control of water hyacinth infestation with regards to fish production

Water hyacinth (Eichhornia crassipes) has been subject of three control methods since its arrival into the Nigerian freshwater lagoon system in 1984 - mechanical, chemical and biological. An assessment of these three methods seems to suggest that mechanical and chemical control methods, both of which being costly, must be applied either solely or integrated to combat the present level of considerable infestation in Nigeria. The biological control methods are advisable for slow, sustained control and can only cope with low levels of infestation. It is thus concluded that the preliminary control method should be mechanical or chemical to effectively abate the nuisance plant, followed by biological control once infestation levels have been sufficiently reduced

Effects of control of C/N ratio by low-cost carbohydrate addition on water quality and pond ecology in freshwater prawn Macrobrachium rosenbergii post-larvae nursing system

An experiment was conducted to evaluate the effects of control of carbon/nitrogen ratio (C/N ratio) by addition of low cost carbohydrate to the water column on water quality and pond ecology in freshwater prawn Macrobrachium rosenbergii post-larvae nursing system. In this experiment, two level of dietary protein 20% and 35% without carbohydrate addition (‘P20' and ‘P35') and with carbohydrate addition (‘P20+CH' and ‘P35+CH') were compared in small ponds of 40 m² area stocked with 20 post-larvae (0.021 ± 0.001g) per m² . Maize flour was used as low cost carbohydrate and applied to the water column followed by the first feeding during the day. The addition of carbohydrate significantly reduced (p< 0.05) ammonia-nitrogen (NH sub(3)-N) and nitrite-nitrogen (NO sub(2) - N) of water in P20 + CH and P35 + CH treatments. It significantly increased (p< 0.05) the total heterotrophic bacteria (THB) population both in water and sediment. Fifty nine genera of plankton were identified belonging to the Bacillariophyceae (11), Chlorophyceae (21), Cyanophyceae (7), Dinophyceae (1), Rotifera (7) and Crustacea (9) without any significant difference (p>0.05) of total phytoplankton and zooplankton among the treatments. Survival rate of prawn was significantly lowest (p<0.05) in P20 and no significant difference (p>0.05) was observed between P20+CH and P35 treatments. Control of C/N ratio by the addition of low-cost carbohydrate to the pond water column benefited the freshwater prawn nursing practices in three ways (1) increased heterotrophic bacterial growth supplying bacterial protein augment the prawn post-larvae growth performances, (2) reduced demand for supplemental feed protein and subsequent reduction in feed cost and (3) reduced toxic NH sub(3)-N and NO sub(2)-N levels in pond nursing system.

Study of bacterial agents on external lesions of cultured Sturgeons in Sngar zone of Gilan Province

This study was carried out to isolate and determine bacterial agents in outer lesions of sturgeons in Shahid Dr. Beheshti sturgeon propagation and rearing center in Gilan province. Five species of sturgeons were studied from viewpoint of lesions. A number of 167 specimens of Beluga, 76 specimens of Persian sturgeon, 27 specimens of Russian sturgeon, 42 specimens of stellate and finally 23 specimens of ship had bacterial lesions in different outer parts of their bodies. After sampling and purification, bacterial cultures and biochemical tests were done. After the isolation of bacteria from lesions, Edwardsiella tarda was selected by means of PCR. To obtain molecular acceptance, a pair of E. tarda special primer, forward primer ETa2-351 and reverse primer (Edwsp-780r) were reproduced. A number of 12 E. tarda DNA sample were identified by PCR. After molecular diagnosis, Persian sturgeon challenged with E. tarda for determination of pathogenesis. Challenge method was done by means of injection of different dilutes of E. tarda into dorsal muscle. Sampling of hematopoietic organs (kidney, spleen and liver) were carried out and located in Boin's fixator to perform pathology survey. Also, in order to survey of existence and effect of E. tarda, sampling of kidney for bacterial culture was done by molecular and biochemical methods. Results showed that the most lesions in all five species belonged to abdominal surface. Skin and scutes of this part were involved in comparison with other parts. Also, It was removed some samples from lesions to pathological survey. Microscopic observations showed some levels of destruction of epidermis layers, necrosis of dermis cells and destruction of muscular layer of skin. On the other hand, invasion of inflammatory cells and haemorrhagic in dermis were clear. Based on biochemical results, Aeromonas sobria, A cavia . A. hydrophila , Acinetobacter lowffii , A.baumanni , A.cakoaceticus, Pseudomonas putida , P fluorescens , P.aeruginosa , Serratia marcescens , Escherichia coli , Enterobacter aerogenes , Edwardsiella tarda , Proteus mirabilis , kelebsiella oxytoca and Staphylococcus sp. were isolated from outer lesions. Results of PCR confirmed that E. tarda was before and after challenge in 200 bp range. LD50, 96h was determined 1.2 x 10^5 (CFU/ml). Pathological experiments showed lesions in the kidney, including hemorrhages, degeneration of glumeruli and tubular epithelia, degeneration and necrosis of interestitium tissue, accumulation of protein casts in the tubular lumen. It was observed haemorhages, engorged blood vessels, congestion of sinusoids, increased of melanine, melano macrophage centers, degeneration and necrosis of hepatocytes in the liver. In the spleen, it was recorded congestion, degeneration, necrosis changes in the white and red pulpa, blood engorged and detachment of ellipsoid wall.

Management of Biesboch reservoirs for quality control with special reference to eutrophication

The three Biesbosch Reservoirs are pumped storage reservoirs, fed with rather polluted and highly eutrophic water from the River Meuse. Air injection at the bottom of the reservoirs prevents thermal stratification, which would otherwise result in serious water quality deterioration. Reservoir mixing also serves as an economic algal control measure; mixing over sufficient depth causes light to play the role of limiting factor and this, combined with zooplankton grazing, keeps the biomass of phytoplankton at acceptable levels. Special problems are caused by benthic, geosmin-producing Oscillatoria species growing on the inner embankment. Rooting up the bottom with a harrow is used as the method of control, based on underwater observations by biological staff trained as SCUBA-divers. With regard to pollutant behaviour the three reservoirs act as a series of fully mixed reactors. This enables the application of kinetic models to describe their behaviour and allows the use of a selective intake policy, e.g. for suspended solids with associated contaminants, ammonia and polynuclear aromatic hydrocarbons. A combination of selective intake and self- purification processes - enhanced by the compartmentalisation of the storage volume in three reservoirs - leads to a striking improvement for many water-quality parameters.

The cost of quinine Cinchona pubescens control on Santa Cruz Island, Galapagos

We analyse the cost of controlling the invasive quinine tree Cinchona pubescens Vahl in the highlands of Santa Cruz Island, Galapagos. Control costs in ten 400 m2 plots formed the basis for estimating the cost of control over the whole island. In the plots, densities were 2100–24,000 stems/ha (stems >150 cm tall) and 55,000–138,000 stems/ha (all size classes combined). Control involved uprooting small plants, and applying of a mix of metsulfuron methyl and picloram to cut stumps or to machete cuts in the bark of larger trees. These methods are presently used by Galapagos National Park field crews to control quinine. Costs (in man hours, herbicide and US$) were related to stem density; the density of stems summed across four height classes was a better predictor of costs than density of any one size class. Regressions (on all size classes combined) formed the basis for predictive models of costs. Costs ranged from $14 to $2225 per ha depending on stem density. The amount of herbicide (active ingredient/ha) that must be applied to high density stands of quinine is higher than typical rates of application in an agricultural setting. The cost of treating all existing plants once across quinine’s known range on Santa Cruz Island (c. 11,000 ha) was estimated at c. US$1.65 million. CDF Contribution Number 1013.

On control of drained weights in some fishery products

Canned and frozen prawns are subjected to compulsory pre-shipment inspection, during which compliance of the products with their declared drained weights is verified. The materials used in the processing of these products being biological in origin, the drained weights are susceptible to variation due to a number of factors. Since determination of the drained weights involves destructive and time consuming procedures, application of control chart for drained weights on the processing line is not possible. The present study has shown that gross weights of the products are significantly correlated with their drained weights and since the determination of the former does not have the disadvantages of determination of the latter, the drained weights can be controlled through the application of control chart for the gross weights.