No abstract

Shrimp production has been affected by disease outbreaks caused by Vibrio sp. bacteria. Using a polyculture system has been proposed as preventive management, but until now, the mode of action by which the organisms in polyculture obtain some benefits was unknown. Some studies indicate that these benefits are related to the immune system in the skin mucus. The present study aimed to determine the antibacterial potential of skin mucus in two tilapia varieties, Oreochromis sp. (marine adapted) and O. niloticus (freshwater), against Vibrio bacteria that affect the shrimp Penaeus vannamei. Skin mucus extracts were obtained from both varieties of tilapia during spring and winter. The extracts were: acidic, aqueous and two organics. In total, 16 extracts were obtained. During the winter season, no antibacterial activity was detected; however, in the spring, the acidic extract from the marine-adapted tilapia inhibited V. parahaemolyticus. Additionally, V. harveyi was inhibited by the acidic and organic extracts from both varieties. The aim of this study was confirmed: tilapia skin mucus has antibacterial activity against Vibrio bacteria, which depends on the tilapia variety, bacterial strain, season and the concentration of colony forming units. SDS-PAGE revealed a protease of 96 kD present in all extracts, even in those without antibacterial activity.

Trypsin from Pacific white shrimp Litopenaeus vannamei is a polymorphic protein composed of three alleles (A, B, and C). The C allele is monomorphic for the first region, while A and B are allelic variations for the second region that are segregated according to Mendelian rules. These three alleles give rise to three individual trypsin phenotypes displayed in sodium dodecyl sulfate polyacrylamide gel electrophoresis: CBA, CB, and CA. The expected frequencies from mating CBA males and females resulted in offspring that consisted of 25% CB, 25% CA, and 50% CBA trypsin phenotypes. To define a management protocol for studying shrimp performance associated with the trypsin phenotype, the goal of this study was to determine if the expected proportions of the three trypsin phenotypes are represented in the population structure at breeding age in 11 hatcheries. Here, we hypothesized that the population structure of the trypsin phenotypes is represented by frequencies that are subject to selection, and it is possible to establish a management protocol to study shrimp performance. A total of 2,828 breeding shrimp from 11 hatcheries were analyzed to describe their population structure. The results showed a high frequency of CBA breeders and a near absence of the CA phenotype in the population structure. To discard the possibility that man‐made selection is the cause of the trypsin phenotype frequency, the offspring of CBA breeders were cultured in nine commercial ponds, and the phenotype frequencies were monitored during 75 d. Interestingly, the CA phenotype was only present during the early stages of culture, which suggests that the population structure is not due to human selection of CBA shrimp in the hatcheries. In this condition, poslarvae production could be directed to make trials that contribute to describe the difference between the culture performance between phenotypes, but not to support the commercial production of larvae with the highest culture performance trypsin phenotype.

No abstract

Correct management of the feeding regime in shrimp aquaculture has been beneficial. Still, when looking for improvement in shrimp performance, the results have been contradictory, and the limits between better growth and independent growth as a function of the feeding regime are not clear. In this study, trypsin and α-amylase activity, as well as an interpretation of the energy utilized for enzyme production, were evaluated in shrimp weighing 1 g. Four feeding groups were set to feed one, two, four, or eight times per day over a month, after which trypsin and α-amylase activities were evaluated during 29 h. Results indicated that the group fed once per day ingested 90% of the feed, whereas the other groups ingested 100%. The α-amylase was not consumed during the daytime in all groups, unlike trypsin. Total trypsin activity was not significantly different between feeding groups, but α-amylase was significantly different. Shrimp fed eight times had an elevated α-amylase activity level that was 2.6 times greater than those fed only once, and 0.8 and 0.5 times greater than those fed four and twice per day, respectively. Feeding more frequently generates a higher use of energy that may or may not be reflected in growth but could be essential for all the energy-dependent metabolic processes required by shrimp.