Unit 15 Lesson 19

Unit 15 Lesson 19 Hatchery Systems of Penaeid Shrimp

Ovaries roots-blower, Boiler nauplius, Phytoplankton zoea

Aeration stainless steel heating tubes spawner mysis zooplankton

B. The Japanese Hatchery Process Nauplii and phytoplankton

When nauplii are found swimming, usually in the afternoon of the second day, potassium nitrate (KNO3) at 2 ppm and potassium phosphate ( K2 HPO4) at 0.2 ppm (total volume ) are applied to accelerate phytoplankton production. This application rate is maintained daily through PL10 (10-day-old postlarvae). With substantial sunlight, plankton growth begins to produce a brownish color in the water as early as late afternoon of the first day of application of the fertilizers. Brown turbidity, gradually increasing day by day, is an indication of normal plankton growth.

B. The Japanese Hatchery ProcessNauplii and phytoplankton Sometimes normal phytoplankton growth is inhibited by lack of sunlight or unknown factors in the water. In the latter case, introduction of mall amounts of fresh seawater may result in immediate resumption(恢复) of the bloom. In the former, the clear polyethylene sheets normally employed to cover the tanks to prevent heat loss and exclude airborne detritus may be removed to admit more intense insolation (暴晒, 日光浴). Removal of the sheets is acceptable so long as the water can be maintained at 28 ℃.

B. The Japanese Hatchery Process Zoea and Nutrition The zoeal stage of P. japonicus goes through three molts

and lasts 4 - 5 days. As long as the plankton bloomcontinues healthy, tank water is maintained as is and no additives other than the chemical fertilizers already mentioned are introduced. The zoea swim constantly forward by action of the swimming legs and drag behind them a threadlike feces.

B. The Japanese Hatchery ProcessZoea and Nutrition

Should the bloom fail, the Japanese introduce shrimp formula feed crumbled into 100-mesh particles. The input rate is 1.5g/10,000 zoea /day on a quantitative basis. Qualitatively, feed can be added at a rate which results in water color (turbidity) similar to that resulting from normal plankton growth. Hirata has achieved good results also with soybean cake which is a byproduct of the brewing (酿造)of soy sauce and a good deal cheaper (in Japan ) than the formula feed.

B. The Japanese Hatchery Process

Mysis and Nutrition The mysis stage lasts three days if conditions are normal; it entails (使必需) three molts. Mysis larvae continue to feed on phytoplankton and will take microzooplankton such as rotifers and oyster eggs and larvae as well.

B. The Japanese Hatchery Process Mysis and Nutrition At the time of appearance of the mysis, new seawater is added to the tank at a rate which increases the depth by 15 cm/day. By PL5 (postlarvae-fifth day), the depth of the water reaches 2 m where it is maintained. The planktonic bloom, if it maintains its proper composition, gr

adually turns the water dark coffee brown. The appearance of “green water” instead indicates a flagellate bloom; if such a

B. The Japanese Hatchery Process Mysis and Nutrition In tanks showing acceptable larval development, the phytoplankton forms noted in order of their relative abundance are Melosira, Nitzschia, Skeletonema, Rhizoselenia and Chaetoceras. Water pH during all phases of larval and postlarval hatchery development remains between 7.5 and 8.5 without any active control being mentioned by Shihueno. Should the plankton bloom fail entirely, soybean cake or formula feed is substituted in the same fashion as that described for zoea (water color approach). Larval development rates on soybean cake may be retarded (延迟) by as much as two days; survival is unaffected.

B. The Japanese Hatchery Process Postlarvae and Nutrition Postlarvae of P. Japonicus gradually shift from an omnivorous diet to a carnivorous one and prefer a pure animal diet by PL5~.6 according to Shigueno. By the PL3~4 stage, planktonic copepods at a density of 6011 along with lower densities of veliger, trocophore, balanus larvae, noctiluca (夜光虫) and polychaete(多毛类) larvae as well as some flagellates occur. These naturally occurring forms are augmented with Artemia saline nauplii and as many as 46-84 nauplii per day may be consumed by shrimp fry in the late mysis and early PL stages. It is important that only the nanplii of Anemia be introduced (no eggs or shells) and that large nauplii not be fed to mysis and early PL shrimp.

B. The Japanese Hatchery Process Postlarvae and Nutrition At PL5~6 minced clam or formula feed replaces Artemia nauplii as the basic feed. Clam meat is expensive and of limited nutritional value after the necessary washing; Shigueno suggests that eventually formula feed my be expected to replace it entirely. During rearing from early PL to PL20-30, the tank water is exchanged at the rate of 20 - 40 % per day. there is no set formula; the rate is varied according to objective and subjective evaluations of water quality. New water is filtered through 60-mesh cloth as it is introduced.

B. The Japanese Hatchery Process Nutrition and Disease Mass kills of cultured larvae in Japan are entirely too common. The disease orgamsm is thought to be Vibrio sp. However, Shigueno feels that it is likely that such epizootics occur primarily as a result of poor nutrition.

B. The Japanese Hatchery Process Nutrition and Disease At present, the Japanese do not practice pure phytoplankton culture and so species compositions in the tank-reared phytoplankton community vary widely and indigestible forms such as Navicula and Coscinodiscus may become dominant; this results in poor larval nutrition. Setaguchi et al have undertaken formula feed experiments to counteract the problem with considerable success.

Also, the Japanese are now reevaluating pure culture phytoplankton approaches using C …… 此处隐藏：6749字，全部文档内容请下载后查看。喜欢就下载吧 ……