Acute toxicity of un-ionized ammonia to milkfish (Chanos chanos) fingerlings

The acute toxicity of un-ionized ammonia to milkfish (Chanos chanos) fingerlings was determined using a static bioassay system. Median lethal concentrations found show that milkfish fingerlings have a high tolerance to ammonia and it is unlikely that levels as high as those employed for the acute exposure would be found to occur under natural conditions. Although the threat of acute toxicological effects induced by ammonia are remote, such conditions might be encountered in stressed natural environments or in heavily loaded aquaculture systems.

Acute toxicity of unionized ammonia to milkfish (Chanos chanos Forsskal) fry

The study was conducted to determine the effects of varying concentrations of ammonia to milkfish fry. Two runs of static 96h bioassays were conducted to determine the median lethal concentration (LC 50) of unionized ammonia (NH₃) to milkfish fry. Test concentrations were based on exploratory 24h and 48h bioassays and were made in three replicates. Reagent grade ammonium chloride (NH₄Cl) was used to adjust the level of unionized ammonia. The 96h median lethal concentration, determined by the Reed Muench method was calculated at 28.029 ppm NH₃ 29.69 ppm. Even at high concentrations of unionized ammonia, most of the fry mortality occurred after 48 to 96 hours exposure. Severe gill damage occurs only at concentrations above 20 ppm, especially above the LC 50. The high LC 50 value obtain shows that milkfish fry has great tolerance to ammonia, that even fry with severely-damaged gills can still recover days after it is returned to favorable culture condition. The result suggest that observed mortalities of milkfish fry under culture conditions are not due to ammonia toxicity.

Year-round and rotational freshwater prawn, Macrobrachium rosenbergii and paddy farming: soil quality, production and economics

A study was carried out at five upazillas (Dumuria, Fakirhat, Pirojpur sadar, Gopalgonj sadar and Kalia) of five southern districts of Khulna, Bagerhat, Pirojpur, Gopalgonj and Narail to understand the comparative production performance and any effect on soil quality in case of year-round golda (Macrobrachium rosenbergii), alternate prawn-paddy and year-round paddy farming. A direct interview of 55 farmers was taken, using pretested questionnaire, and soil samples were taken from selected farms before and after each crop. Among the five upazillas, farmers in Gopalgonj sadar and Kalia are not practicing year-round golda. Rotational golda-paddy farming has been recorded to result in maximum profit, with the highest of Tk. 310,912/ha/year in 2003 at Dumuria. Only paddy farming is less profitable than other two cropping patterns, irrespective of study sites. The nutrient status of soil in rotational golda and paddy farming has been found improved, compared to that of only golda or paddy farming.

Toxicity test: Sponge toxin on tilapia fry

The research was conducted to determine the toxicity of extracts from five Philippine species of marine sponges on tilapia Oreochromis niloticus fry. It was found out that the most potent was the methanol extract of Dysidea herbacea, it kills with the least toxin and at the shortest time.

The toxicity of four insecticides and a herbicide under tropical conditions

The toxicities of four insecticides and a herbicide to Tilapia macrochir were tested in the laboratory. The 24 hour LC50's were estimated as follows: Endrin 20% ,0.008 ppm; Lindane 5% granules, 4.6 ppmm; Synexa 50 (HCH) 50%), 5.6 ppm; Synex 25 (HCH 25%), 14.8 ppm; TOK herbicide (Nitrofen), 100% survival for 24 hours at 100 ppm. These estimates agree with results obtained by other workers elsewhere in the world. The laboratory determination of toxicity is important in estimating the direct effects of poisonous substances on fish, but other indirect effects may result from their use. These should be investigated in the field.