Artificial substrata increase pond farming density of grass carp (Ctenopharyngodon idella) by increasing the bacteria that participate in nitrogen and phosphorus cycles in pond water.

Zhifei Li,Kai Zhang,Deguang Yu,Ermeng Yu,Guangjun Wang,Jun Xie,Wangbao Gong

doi:10.7717/peerj.7906

Abstract

Aquaculture has become a primary method to produce various aquatic products, and intensive aquaculture technologies have become commercially important. To improve the efficiency of intensive aquaculture per unit area without reducing the growth rate of cultured fish, the present study explored the potential of artificial substrata in ponds. Our results showed that the concentrations of total nitrogen (TN) and total phosphorous (TP) in the ponds with different stocking densities of grass carp were lower than those in the control group in most cases. Further, the feed conversion rate of grass carp was significantly reduced by introducing these artificial substrata, and the culture density could be significantly increased without reducing the growth rates of these fish. Artificial substrata also significantly enriched specific bacteria and changed the structure of the microbiota in pond water. The relative abundance of Proteobacteria was significantly increased, and bacteria closely related to N and P cycles, such as Hyphomicrobium, Chitinimonas, Legionella, Shewanella, Roseiflexus, and Planktothrix were significantly enhanced. These results showed that the artificial substratum could increase TN and TP removal in aquaculture pond water by enriching N and P cycle-related bacteria, thus significantly increasing the specific growth rate of grass carp and significantly reducing their feed conversion rate. Finally, the stocking density of grass carp and the yield per unit area of pond could be increased without reducing the growth rate.

Highlights

Subjects Aquaculture, Fisheries and Fish Science, Bioinformatics, Ecology, Microbiology, Freshwater Biology Keywords Artificial substratum, Grass carp, Aquaculture, Nitrogen and phosphorus cycles, Microbiota
To further increase the yield of grass carp per unit pond area without affecting the growth rate and to analyse the potential role of microbial flora that are enriched by the artificial substratum, the present study used grass carp farming density as a variable to determine whether this artificial substratum could effectively alleviate the deterioration in aquaculture water quality caused by the increased culture density
We further demonstrated that the presence of an artificial substratum could effectively increase the culture density while maintaining the growth rate of grass carp (Fig. 2C), increasing the yield per unit pond area

Summary

Introduction

Subjects Aquaculture, Fisheries and Fish Science, Bioinformatics, Ecology, Microbiology, Freshwater Biology Keywords Artificial substratum, Grass carp, Aquaculture, Nitrogen and phosphorus cycles, Microbiota. Introducing artificial substrata that improve microbial attachment can significantly promote the growth of aquaculture species while restoring water properties in situ (Bo et al, 2010; Audelo-Naranjo, Martínez-Córdova & Voltolina, 2010; Schveitzer et al, 2013; Kumar et al, 2015; Li et al, 2017). The main ways that artificial substrata promote fish growth include the following: reducing ammonia and nitrite concentrations in farming water through the assimilation and dissimilation of microorganisms that adhere to the surface of artificial substrata (Arndt et al, 2002; Zhang et al, 2019); providing natural feed to farming organisms through the presence of adherent microorganisms on the surface of artificial substrata, such as bacteria, fungi, algae, protozoa, and zooplankton (Azim et al, 2002); reducing energy consumption caused by stress reactions through the physical shelter provided by these structures (Huang et al, 2013; Pandey, Bharti & Kumar, 2014). To further increase the yield of grass carp per unit pond area without affecting the growth rate and to analyse the potential role of microbial flora that are enriched by the artificial substratum, the present study used grass carp farming density as a variable to determine whether this artificial substratum could effectively alleviate the deterioration in aquaculture water quality caused by the increased culture density

Methods

Results

Conclusion