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    • Article

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

      ER Cruz - SEAFDEC Aquaculture Department Quarterly Research Report, 1981 - Aquaculture Department, Southeast Asian Fisheries Development Center
      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.
    • Conference paper

      Hematological and histopathological changes in Oreochromis mossambicus after exposure to the molluscicides Aquatic and Brestan 

      ER Cruz, MC de la Cruz & NA Suñaz - In RSV Pullin, T Bhukaswan, K Tonguthai & JL Maclean (Eds.), The Second International Symposium on Tilapia in Aquaculture, 16-20 March 1987, Bangkok, Thailand, 1988 - Department of Fisheries; International Center for Living Aquatic Resources Management
      Duplicate static 96-hour bioassays were conducted to determine the median lethal concentration for Oreochromis mossambicus (LC50) of two organostannous molluscicides, commonly used in fishponds: Aquatin and Brestan. O. mossambicus was more sensitive to Brestan. The acute toxicity of both Aquatin and Brestan ceased towards the end of 96 hours. The 24, 48, 72 and 96 hour LC50’s were 4.01, 3.97, 2.95 and 2.58 ppm formulated product for Aquatin and 0.35, 0.18, 0.10 and 0.09 ppm for Brestan, respectively. The computed safe concentrations for Aquatin and Brestan are 0.30 and 0.01 ppm, respectively.

      Exposure to lethal concentrations of Aquatin resulted in an immediate reduction in hemoglobin and hematocrit levels. Hemoglobin content was likewise lower in Brestan-exposed fish, whereas their hematocrit level was higher than that of the control fish.

      Histological analyses of gills, intestine, liver and kidney showed pathological changes even in sublethal levels tested. Damage became severe with increasing concentration of the pesticide. The behavior and symptoms exhibited by the fish and the physiology of hematological and histopathological changes are discussed.
    • Book

      Recommended practices for disease prevention in prawn and shrimp hatcheries 

      GD Lio-Po, RD Fernandez, ER Cruz, MCL Baticados & AT Llobrera - 1989 - Aquaculture Department, Southeast Asian Fisheries Development Center
      Series: Aquaculture extension pamphlet / SEAFDEC Aquaculture Department; No. 3
      Disease in prawn is any abnormal condition which may affect adversely the appearance, growth, and function of the animal. It may or may not result in mortalities. Disease outbreaks occur commonly in different culture systems such as hatcheries and grow-out ponds.

      Disease develops through the interaction of the prawn (the host), the causal agent (the pathogen), and the environment. In the presence of a susceptible host, a pathogen and predisposing environmental conditions (poor water quality, inadequate food, frequent handling, overstocking), disease is very likely to occur. Improved environmental conditions, healthy prawns and absence of disease agents would therefore lessen the chance of a disease outbreak.

      The causal agents may be pathogenic organisms (viruses, bacteria, fungi, protozoa, helminths, microcrustaceans) or nonpathogenic adverse environmental conditions (extreme temperatures, low oxygen levels, chemical poisons). Living disease agents cause infectious disease which generally result in gradual mortalities. Non-living disease agents cause non-infectious diseases that result in sudden mass mortalities.

      The environment determines the balance between the prawn as host and the disease agent. Microorganisms are always present in the water and some of them cause disease only when the prawn has been weakened through exposure to stressful environmental conditions.

      Hatchery personnel should realize that they themselves could transmit disease through their contaminated hands, clothing, and footwear. Equipment such as water pumps, blowers, pipes, and materials such as scoop nets, water hoses, pails, glasswares are also possible carriers of disease agents. Spawners, live natural food like diatoms, rotifers and brine shrimp, and artificial diets could also be vehicles of disease transmission.

      The prawn culturist, thus, must be able to manage the environment and make it favorable for the prawn. Hatchery management should, therefore, include operation procedures that will reduce the possibility of disease development during larval rearing. This manual recommends practices for disease prevention to prawn hatchery operators and technicians.