Congqiang Luo

The yellowfin seabream (Acanthopagrus latus) is an economically important commercial mariculture fish in China and Southeast Asia. Only a few simple sequence repeats (SSRs) of A. latus have been isolated and reported, which has hindered breeding progress. A total of 318,862 SSRs were isolated and characterized from the A. latus genome in this study. All SSRs were 9,069,670 bp in length, accounting for 1.32% of the genome. The density and frequency of SSRs were 468.40 loci/Mb and 13,323.19 bp/Mb, respectively. The major SSRs were dinucleotides (accounting for 76.92%), followed by trinucleotides (15.75%). The most abundant SSR motif was (AC)n (168,390, accounting for 53%), with the highest frequency (245.78 loci/Mb) and density (7304.18 bp/Mb). Most SSRs were located in non-coding regions, such as intergenic regions (34.54%) and introns (56.91%). SSR-containing exons were distributed into 51 gene ontology (GO) terms and significantly enriched in immunity- and growth-related pathways. A total of 217,791 SSR markers were successfully designed. Nine SSR markers were amplified in 29 A. latus individuals, and eight of them possess high polymorphism. The cross-species transferability of 33 out of the 37 tested loci were successfully amplified in Acanthopagrus schlegelii. These results lay the foundation for the molecular marker-assisted breeding and genetic information assessment of A. latus.

This experiment aimed to study the effects on liver tissue structure and immune performance of grass carp Ctenopharyngodon idellus when the common reed Phragmites australis is in its diet, instead of wheat Triticum aestivum L. Seventy-two healthy grass carps (145.52 ± 2.56 g) were randomly divided into three groups according to their body weight. Fishes in each group were fed an essential diet with 0% (control group), 50% and 100% (test group) common reed, instead of wheat, respectively. After feeding for 41 days, the changes of serum biochemical indices, liver tissue structure and immune related indices of grass carp were detected. The results showed that, compared with the control group, the activities of serum alanine transaminase (ALT) and aspartate transaminase (AST) in the substitution groups were significantly increased (p < 0.05), but still at a normal level. The contents of total protein, albumin and globulin did not change significantly (p > 0.05). Compared with the control group, the liver cells of grass carp in the substitution groups had clear boundaries, tight arrangement and less vacuolation. The contents of serum interleukin-1 (IL-1) and complement 3 (C3) in the 100% substitution group were significantly higher than those in the control group (p < 0.05), and the contents of liver IL-1 and total complement (CH50) in the 100% substitution group were significantly higher than those in the control group (p < 0.05). The contents of IL-1, C3 in serum and IL-1, CH50 in liver in the 50% substitution group were significantly higher than those in the control group (p < 0.05). The mRNA relative expression levels of C3, IL-1, MHC-I and interferon (IFN) in the head-kidney, kidney, liver and spleen of grass carp were significantly affected by feeding the grass carp with different common reed substitution ratios (p < 0.05). In summary, common reed, instead of wheat, in feed can improve the liver tissue structure, and increase the non-specific immune response level, of grass carp.

Freshwater cyanobacterial blooms (e.g., Microcystis blooms) constitute a major global environmental problem because of their risks to public health and aquatic ecological systems. Current physicochemical treatments of toxic cyanobacteria cause the significant release of cyanotoxin microcystins from damaged cells. Biological control is a promising eco-friendly technology to manage harmful cyanobacteria and cyanotoxins. Here, we demonstrated an efficient biological control strategy at the laboratory scale to simultaneously remove Microcystis and microcystins via the combined use of the algicidal bacterial filtrate and the microcystin-degrading enzymatic agent. The algicidal indigenous bacterium Paenibacillus sp. SJ-73 was isolated from the sediment of northern Lake Taihu, China, and the microcystin-degrading enzymatic agent (MlrA) was prepared via the heterologous expression of the mlrA gene in the indigenous microcystin-degrading bacterium Sphingopyxis sp. HW isolated from Lake Taihu. The single use of a fermentation filtrate (5%, v/v) of Paenibacillus sp. SJ-73 for seven days removed the unicellular Microcystis aeruginosa PCC 7806 and the native colonial Microcystis strain TH1701 in Lake Taihu by 84% and 92%, respectively, whereas the single use of MlrA removed 85% of microcystins. Used in combination, the fermentation filtrate and MlrA removed Microcystis TH1701 and microcystins by 92% and 79%, respectively. The present biological control thus provides an important technical basis for the further development of safe, efficient, and effective measures to manage Microcystis blooms and microcystins in natural waterbodies.