Massive nauplii production in Litopenaeus setiferus by means of natural matings has not been reported. The main reason is the low spermatophore attachment rate that has been associated with male sterilization because of male reproductive tract degenerative and the male reproductive melanization syndromes (MRTDS and MRMS). This information indicated both syndromes could be related to the captivity and management stress that affects the immune system and the physiological state of shrimp. We used some blood metabolic variables, sperm quality, and immune response as indicators of captivity stress in adult males of L. setiferus. A comparison between freshly captured shrimp with shrimp maintained in the laboratory for 7 days at two temperatures were examined. Glucose and calcium were not different between fresh and acclimated shrimp at either temperature (P > 0.05). A reduction in triacylglycerol, proteins, and cholesterol was observed in acclimated shrimp in comparison with base line shrimp (P < 0.05). Lactate was reduced only in shrimp acclimated at the lower temperature. Sperm quality was not significantly different between base line samples and acclimated shrimp. The immune system was altered in acclimated shrimp at both temperatures. A reduction in total haemocytes, granular cells, and semigranullar cells was measured in acclimated shrimp in comparison with base-line shrimp. In contrast, a higher phenoloxidase activity (proPO) was observed in acclimated shrimp, indicating that regulatory mechanisms of immune system of those shrimp were altered by captivity conditions. The blood metabolic variables indicated that captive shrimp were affected nutritionally more than physiologically. The immune response showed the nutritional effect or another management factor reduced the cellular defenses and altered the molecular mechanisms associated with melanin production. This could be related to the melanization syndrome observed in previous studies. A new sequence to explain the appearance of the male reproductive shrimp syndromes of L. setiferus was proposed. (C) 2001 Elsevier Science B.V. All rights reserved
