Effect of salinity on natural community and production of Litopenaeus vannamei (Boone), within experimental zero-water exchange culture systems

Recent efforts have been made to culture marine shrimp in systems operating under low or zero‐water exchange and with decreased water salinity. The aim of this study was to investigate the impact of various salinity levels on qualitative and quantitative characteristics of the natural community and, more particularly, ciliated protozoa, and compare this information with shrimp growth and survival. Tanks with 9‰ salinity were characterized by a higher pH, but also by a significantly higher concentration of chlorophyll a (Chl a) per weight of suspended matter (1.93 ± 0.72 µg Chl a/mg TSS) than tanks with 18‰ (1.29 ± 0.68 µg Chl a/mg TSS) or 36‰ (1.37 ± 0.61 µg Chl a/mg TSS) salinity. Concentrations of ciliates (max 6000 cells mL^?1) showed considerable fluctuations over the sampling period, reflecting the impact of water salinity, dynamic interactions between ciliates and their diverse roles within the shrimp production system. There was no significant difference between survival rates of shrimp reared at 9‰, 18‰ or 36‰, but decreasing salinity from 36‰ to 9‰ led to a significant decrease in final shrimp body weight (from 13.40 ± 0.26 g to 10.23 ± 2.72 g). Future work should address the potential of ciliates as an indicator of aquaculture water quality, as is currently being done in the wastewater industry, and the contribution of ciliates as food sources.     

Effect of Shrimp Stocking Density on Size-fractionated Phytoplankton and Ecological Groups of Ciliated Protozoa within Zero-water Exchange Shrimp Culture Systems

Zero‐water exchange shrimp culture systems are being investigated to reduce water and pathogens input and effluent output. The relative abundance and diversity of ciliates have been used as indicators of water quality and ecosystem dynamics in natural systems; however, their occurrence and role in shrimp production systems have not been investigated. The objectives of this research were to describe the succession of the ciliate community in a shrimp grow out system, to investigate the impact of increasing shrimp stocking density on the characteristics of the ciliated protozoa community, and to correlate this with shrimp performance. A growth trial with Litopenaeus vannamei was conducted outdoors with zero‐water exchange and three stocking densities (50, 75 and 100 shrimp/m²). In all treatments, free‐swimming ciliates were dominant in the early weeks, while substrate‐associated ciliates appeared later. The 100 shrimp/m² treatment exhibited a lower abundance of free‐swimming ciliates but higher abundance of hypotrichous ciliates in the second half of production and higher shrimp mortality and lower shrimp growth in the last 2 wk. These results provide a preliminary examination of the role of ciliates in shrimp culture systems and direction for future work in determining the role of protozoa as indicators of water quality.     

Determination of microbial community structures of shrimp floc cultures by biomarkers and analysis of floc amino acid profiles

Simple, rapid and reliable methods are required to monitor the microbial community change in aquatic pond for better animal performance. Four floc (suspended organic matter) samples were collected from outdoor raceways and tanks used for culturing Pacific white shrimp Litopenaeus vannamei. Twenty‐two chlorophyll (Chl) and carotenoid pigments were separated, identified and quantified using high‐performance liquid chromatography–ultraviolet/Vis‐mass spectrometry in the freeze‐dried floc samples. Algal community composition (diatoms, chlorophytes, cyanobacteria, dinoflagellates and cryptophytes) was determined by measuring concentrations of the respective taxonomic biomarkers (carotenoid fucoxanthin, lutein, zeaxanthin, peridinin and alloxanthin) as independent variables and Chl a as the dependent variable using a multiple regression model. This analysis found that the phytoplankton community of the floc samples from two groups of shrimp tanks (32 g L^?1‐salinity) were diatom‐dominated (81.7% and 84.4%); and two floc samples from shrimp raceways (5 and 18 g L^?1‐salinity) were chlorophyte‐dominated (75.4% and 82.3%). Assessment of total algal and bacterial biomass by quantification of Chl a and muramic acid, respectively, indicated that the 18 g L^?1‐salinity raceway sample was bacteria‐dominated, whereas the other three floc samples were algae‐dominated. Sample protein quality was evaluated by its essential amino acid (AA) score and index. Arginine and lysine were found to be the two most limiting AAs for all floc samples.