Changes in metabolic and immunological variables of wild and pond-reared southern white shrimp Litopenaeus schmitti adult males during continuous reproductive activity

Abstract

Reproductive performance of male southern white shrimp Litopenaeus schmitti decreased over time possibly attaining a reproductive exhaustion that results in a lower physiological condition that includes a decreased immune response capacity. Several indicators of immune and metabolic status such as phenoloxidase activity (PO), total hemocytes count (THC), hemoagglutinating activity (HA), total proteins, and glucose concentration in the hemolymph were analyzed in wild and pond-reared adult males at 3, 30, and 60 days after introduction to a production cycle in a commercial hatchery. High PO activity, high levels of glucose, and low levels of protein in the hemolymph suggest a general stress condition at the beginning of the production cycle because of the manipulation involved when animals were transferred to the hatchery. As indicated by initial levels of glucose, wild shrimp are more susceptible to such stress. After one month, all indicators suggest optimal conditions for shrimp, which, however, deteriorated in the second month when higher PO activity and lower levels of THC, hemoagglutinating activity, glucose, and proteins were observed, compared to values at 30 days. These results indicate that after a certain period under laboratory conditions associated with high reproductive activity, males of L. schmitti have a depressed overall physiological status and should be replaced.

Reconsideration of phenoloxidase activity determination in white shrimp Litopenaeus vannamei

“…Such artificially induced PO activity in the EDTA-containing plasma obviously does not represent the actual PO activity of the organism, but has also been used in recent studies [9,13]. Therefore, it is suggested that PO activity reported in previous studies [4,5,9,13] should be reconsidered.…”

“…Although the inhibition effect of EDTA on PO activity has been reported in previous studies [12], EDTA-containing anticoagulant has still been used to separate plasma for PO activity assay in recent studies [4,5,9,13]. In this study, PO activity (35.36 AE 4.53 U ml À1 hemolymph) in the sample prepared with EDTA-containing anticoagulant, is only 6% of that in the EDTA-free sample (604.56 AE 53.12 U ml À1 hemolymph), and independent t-tests indicate that PO activity is significantly inhibited by EDTA (P < 0.05) ( Table 1).…”

“…All these factors, if not in a proper range, can affect the accurate determination of PO activity. Moreover, the inhibition effect of EDTA on PO activity [12] is most probably ignored since EDTA anticoagulant has still been used for separating plasma samples in recent studies [4,5,9,13]. Furthermore, we noticed that the assayed PO activity in the same preserved plasma could obviously change when it was assayed at different times.…”

“…The detection of PO activity in plasma sample was carried out kinetically using a spectrophotometer (in triplicate) by recording the formation of dopachrome from L-DOPA according to previous study with some modifications [5]. L-DOPA solutions (3 mg ml À1 in 0.1 M potassium phosphate buffer [PPB]) with graded levels of pH from 5.8 to 7.8, as well as those (pH 6.6) with graded final concentrations of 0.06, 0.5, 1, 1.5, 2, 2.5 and 2.95 mg ml À1 in reaction systems, were used to test for their effects on the assayed PO activities.…”

“…In general, PO activity is determined by artificially activating proPO (normally by trypsin) released by lysing the separated hemocytes and then centrifuging with high force [3]. PO activity is also assayed directly using plasma without the activation by trypsin [4,5]. In our recent studies, we noticed that PO activity in plasma is nearly 40 times higher than the artificially activated PO activity in hemocytes of Litopenaeus vannamei (unpublished data).…”