Comparative Study of the Gut Contents of Penaeus japonicus Bate 1888 (Decapoda: Penaeidae) In Semi-Intensive Culture and In Brackish Water Wild Environment

Abstract

The trophic adaptability of a species may influence its dispersion potential and the ability to invade foreign territories. Understanding the factors that facilitate trophic adaptability may help the provision of forecasts about the potential dispersion of allocthonous species, even in a warmer and acidified world, according to the current trends of global changes. Various studies demonstrated the adaptability of Penaeus japonicus Bate to variable feeding regimes under natural conditions. To optimize artificial diets for the aquaculture of Penaeid shrimps, gut content data of specimens cultured in ponds were compared to contents from shrimps fed on natural macro benthic communities in a brackish-water lagoon. In addition, the feeding adaptability of this shrimp to scarcely diversified benthic associations was tested in aquaculture ponds. Our comparative analyses confirm that P. japonicus feeding pattern may be largely adapted to variations in the available benthic organisms, in different management conditions. Keywords: Penaeus japonicus; Food; Brackish water; Culture; Adaptability; Marsupenaeus japonicus Material and MethodsFive ponds were set in Cammarata (Lesina, Southern Italy) (Figure 1). The first 4 ponds (100 m 2 each one) were managed in semi-extensive conditions, at density of 2.5; 1.5; 2.5; 1.5 post larvae (PL22) per square meter, respectively; the fifth one (200 m 2 ) was managed in extensive conditions, at a density of 12 postlarvae (PL22) per square meter. Water was partially changed daily, by pumping from the adjacent lagoon, in order to promote correct environmental conditions for the grow-out of the shrimps [17] and the development of benthic fauna and flora driven by larvae and various organisms present in the lagoon. The finest rate of changes was determined by measuring selected chemical and physical parameters, i.e., temperature, salinity, pH, dissolved oxygen, dissolved nutrients. In particular, changes were performed to assure consistence of the above-mentioned parameters in comparison to the natural ones, measured in the lagoon [18]. To perform the gut content analyses, three collections of shrimp were obtained in the early night from each pond, to obtain individuals containing undigested prey. The first sample refers to shrimps aged 6 weeks, the second one refers to shrimps aged 12 weeks, and the last one refers to adults sampled a few days before the end of the experiment.Samples were immediately transferred in the laboratory and deep-frozen. Each specimen was measured (total length), weighed, and finally sacrificed, fixed and dissected for the analysis of the gut contents. A presence-absence matrix was compiled, taking into account each specimen sampled and each food item identified in its stomach, according to Zupo et al. [2]. Data were managed by means of a MS-Excel spreadsheet and compared with those obtained by previous authors [9,11,16] In order to obtain quantitative information about the trophic needs of shrimp of different ages, the feeding index "FI" [19] was also cal...