Effect of Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) on Growth, Survival Rate and Histopathological Changes of Pacific White Shrimp (Litopenaeus vannamei)

Abstract

The effect of Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) on the growth and survival rate of Pacific white shrimp (Litopenaeus vannamei), shrimp larvae from broodstocks raised in an earthen pond infected with IHHNV according to the results of a polymerase chain reaction (PCR) test were raised in two experimental ponds at the stocking density of 70,000 shrimps per 1,600 square meters, or 44 shrimps per square meter. The results were compared with shrimp larvae from imported specific pathogen free (SPF) broodstocks, raised in two control ponds at the stocking density of 120,000 shrimps per 1,600 square meters, or 75 shrimps per square meter. The salinity in all the ponds was ranging from 3 – 6 ppt. and the shrimps were raised with commercial pellet feed. After 30 days some of the IHHNV-infected shrimps began to show abnormalities such as bent or deformed rostrums, wrinkled walking legs, cuticular roughness, and other cuticular deformities. Most of these shrimps were also smaller than the others in the same pond. As time went on the number of shrimps with these abnormalities in the experimental ponds rose continuously. Those in the IHHNV-infected ponds that did not display clinical signs of abnormalities still grew at a slower rate than the shrimp from SPF broodstocks. The difference was quite apparent after 70 days. When the shrimp in the two IHHNV-infected ponds were harvested after120 days, the average yield was 1,882.79 kg/ha. The average survival rate was only 44.17% the feed conversion rate (FCR) was 1.75. The shrimp from SPF broodstocks were harvested after 100 days. The average yield was 7,719.38 kg/ha. The survival rate was 81.99 % and the FCR was 1.35. There was a statistically significant difference between the growth rates and survival rates of the two groups (p<0.05). Histopathological studies and in situ hybridization assays of the shrimp that displayed clinical signs revealed Cowdry type A and intranuclear inclusion bodies in the cells of the ectodermal tissues (gills, epidermis and nerve cord) as well as in the mesodermal tissues (hematopoietic organ, antennal gland and lymploid organ) and the endodermal tissues (hepatopancreas). The shrimp that came from SPF broodstocks did not have any visible abnormalities.