Aim: to serve as a general guide to the prevention and treatment of diseases encountered during larval rearing (supplemental to the specific problems referred to the section on Larval rearing).

• All diseases can be considered the end result of an imbalance in the relationship between the shrimp, the environment and the disease agent.
• The primary goal should be to minimize stress and reduce prevalence of disease agents by maintaining the environmental quality in the hatchery.
• Proper attention to water quality control and exchange, siphoning, aeration, feeding control, the use of probiotics and general environmental management should help prevent most diseases from occurring and should be the first line of defence in treating them.
• However, some diseases will occur and there are remedies for some of them.
• Although viruses do not typically cause many losses during the larval rearing phases (except perhaps BMNV), most viruses cannot be treated once they occur, and will reduce the quality of PL produced and stocked into the farms.
• Viral screening (through PCR or other methods) is therefore required to ensure that broodstock and nauplii, and ultimately the PL produced by the hatcheries are virus free. Although, the current lack of facilities and demand is hampering this goal, this project aims to help establish and operate such facilities.
• Meanwhile, viral presence can be reduced by stress-reduction techniques, including proper disinfection of the inlet water, the eggs/nauplii stocked and the feeds used; enhanced water exchange and addition of immunostimulants (i.e. probiotics, ß-glucans and nucleotides) in the diet. Chemical additives that can be used directly in the larval rearing tanks to help control viral presence include Virkon-S or Sanocare PUR at 0.3–1 ppm, povidone-iodine at 5 ppm or formalin at 5–30 ppm.
• Bacteria originate from the same sources as viruses and can be controlled through similar stress-reducing techniques. Some nonantibiotic chemicals such as Sanocare Pur or Virkon-S at 0.3–1 ppm, EDTA at 5–30 ppm, chloramine-T at 2–5 ppm and povidone-iodine at 5 ppm may assist in reducing bacterial numbers.
• Filamentous bacteria such as Leucothrix can be controlled by adding copper sulphate (0.1–1 ppm for 1 h) or Cutrine plus (0.5 ppm) or 0.5–1 ppm (benzalkonium chloride (BKC).



• Bacteriology laboratories are required, either under the Bangladeshi DOF or the SHAB, or even within the individual hatcheries, so that the sources of bacteria coming into the hatchery can be identified and useful methods for their control implemented.
• Fungi such as Lagenidium and Fusarium can be controlled using regular applications of 0.05–0.1 ppm of Treflan, 0.3 ppm of Sanocare PUR or 5 ppm of Microcide (and steam cleaning the tanks).



• Protozoans such as Vorticella and Epistylis can be controlled using baths of formalin (10–30 ppm for 1 h) or copper sulphate (0.1–1 ppm for 1 h), or additions of Cutrine plus (0.5 ppm) or Proto-D at 5–10 ppm.