Microbial communities associated with Zoea-2 syndrome and White feces syndrome in P. vannamei farming

Abstract

Shrimp aquaculture is witnessing production losses due to several emerging diseases in Penaeus vannamei farming both at hatchery and grow-out stages. Diseases are caused due to multiple factors, which include biotic, abiotic and managemental factors (Alavandi et al., 2019; Millard et al., 2021) and in many cases, the etiology is unknown. One such disease commonly observed in hatcheries is zoea-2 syndrome.

Zoea-2 syndrome (ZS) reported since 1990 has become a significant challenge to shrimp larviculture. Recently in India, especially after the introduction of P. vannamei, Zoea-2 syndrome has emerged as a serious threat and severely affected the shrimp larval production. This syndrome is characterized by reduced feeding and impaired metamorphosis and causes delayed molting and mass mortality. Zoea-2 syndrome affected larvae observed to stop feeding suddenly after 36-48 hrs of zoea I stage, then exhibit clinical symptoms and mortality. The clinical signs of Zoea-2 syndrome include loss of appetite, empty gut with no fecal strands, arrested peristaltic movement of gut, inflammation in the intestinal epithelium and white balls or white spheres like structures in the gut. The loss due to zoea-2 syndrome in a 100 million nauplii stocking capacity hatchery was reported to be approximately ₹ 1.2 to 4.0 million Indian rupees in 2016 (Sathish Kumar et al., 2017). So far, incidences of zoea-2 syndrome were only associated with Vibrio harveyi and Vibrio alginolyticus (Vandenberghe et al., 1999). In our earlier study, among other vibrio isolates V. alginolyticus was found to be significantly associated and no known pathogen was found to be causally associated with this syndrome (Sathish Kumar et al., 2017). Thus, etiology and pathology of zoea 2 syndrome endure to be unresolved for almost three decades. Eventually, this syndrome results in mass mortality with a pattern of gradual, progressive manner increasing with day-by-day stocking to the maximum of 70-90%.

Another important disease of grow-out ponds that has become a concern in recent years is white feces syndrome (WFS) which affects the juvenile and adult stages of shrimp in aquaculture farms. Reduced feeding, growth retardation, white gut and loose carapace with floating white feces on the surface of the pond are the symptoms of WFS (Tang et al., 2016). The disease occurs commonly after 30-40 days of culture which may also be accompanied by mortality of animals (Sriurairatana et al., 2014). WFS occurrences were reported to be associated with aggregated transformed microvilli (ATM) structures resembling gregarine worms, vibriosis, Enterocytozoon hepatopenaei (EHP), blue-green algae, and fungi (Sathish Kumar et al., 2022). Disease manifestations are noticed even in the absence of these agents (Wang et al., 2020). Studies on intestinal bacterial communities of WFS shrimp indicated less diverse (Hou et al., 2018), more abundant V. sinaloensis and V. parahaemolyticus (Wang et al., 2020) and other potential role of pathogenic bacteria (Zeng et al., 2020).

The 16s rRNA amplicon sequencing offers to provide diversity and dynamics of both culturable and unculturable microorganisms of a habitat, which is not possible through traditional laboratory approaches (Martínez-Porchas and Vargas-Albores, 2017). In this study, 16s rRNA amplicon sequencing was carried out for ZS and WFS which affect hatcheries and grow-out ponds, respectively. This is the first report on the 16s amplicon sequencing data of zoea-2 syndrome and the recovered sample profiles of white feces Syndrome. The sequencing information generated from this study is useful for understanding microbial communities associated with two important diseases and forms basis for possible future designing of preventives and treatments.