Abstract

As the field of commercial shrimp aquaculture develops, identification and evaluation of potential measures of disease resistance in candidate aquaculture species, or strains of those species is of increasing importance. Although the primary function(s) of humoral lectins in shrimp is not clear, it is believed that a secondary function may be opsonization of bacteria and other foreign particulates entering the hemolymph of the animals, hence they function at least in part as defense molecules. Previous studies in this laboratory using the brown shrimp (Penaeus aztecus) as a model, demonstrated a form of adaptive response in that the pattern of depression and recovery of lectin levels was different in animals challenged by injection of erythrocyte or bacterial antigen for the first time from the pattern observed in animals challenged a second time (30 days after the first challenge).¹ Specifically it was observed that after the second challenge, recovery of lectin levels to levels at or above normal levels was more rapid. It was hypothesized that ability to demonstrate this adaptive response (although it is not antigen-specific) might provide an indicator of enhanced immune defense abilities against potential pathogens, hence might be an evaluative tool for candidate shrimp strains for use in aquaculture.

Penaeus vanammei is a potentially important aquaculture species. This laboratory has for several years been involved in a consortial study of this species. Other laboratories within the consortium are engaged in selective breeding efforts to develop and evaluate strains of Penaeus vanammei which are resistant to selected pathogens. One such study has targeted Tauravirus, an important viral pathogen in Penaeus species. Colleagues at the Gulf Coast Research Laboratory kindly made available to this laboratory animals from two groups. The first group included survivors of an experiment in which animals from various broods were exposed to Tauravirus. The second group represented unchallenged animals from the same or related broods. Shrimp from each group were injected with 5 μl of sheep red blood cells (1x10⁷ cells/ml). Following injection, the shrimp were sacrificed in groups of five for up to 120 hours at set intervals of time and agglutination titers against sheep, rabbit, human (type O+), mouse, and rat erythrocytes in the extracted hemolymph was determined. The same general pattern was seen in both the Tauravirus-exposed and non-exposed P. vanamme. Upon a primary injection with sheep erythrocytes, lectin titers decreased to a minimum titer reached, on average, 16 hours post-injection; lectin titers then proceeded to increase and stabilize at normal titers, which were attained 96-120 hours post-injection. A secondary injection given 30 days after the primary injection caused a sharper, more rapid decrease in titer with a minimum titer reached at 6 hours and an increase to normal titer by 24 hours post-injection. Control P. vanamme, held for 30 days in aquaria prior to receiving the primary injection, showed a pattern similar to the animals that received the primary injection immediately after being placed in the aquaria. Although both trials showed similar patterns in lectin titers after primary and secondary injection, the non-Tauravirus-exposed P. vanamme had higher overall titers than the survivors of the Taura virus exposure.

Acknowledgements

This research was supported by a grant from the USDA.

References

1.  Middlebrooks BL, Lee Yeuk-Mui; Li Min, Ellender RD. 1994. Effects of repeated immunization and wound trauma on changes in hemolymph agglutinin levels in brown shrimp (Penaeus aztecus). Primordial Immunity: Foundations For the Vertebrate Immune System 712: 358-360.