Poecilia reticulata is an important species in the global ornamental fish trade, known for its environmental adaptability and bright adult coloration. However, research on sex-dependent background color choice in this species remains limited, constraining the understanding of visual-environment requirements across sexes. In this study, we used a circular six-color maze (red, yellow, blue, green, black, and white) to independently test male and female P. reticulata at first sexual maturity. The results showed that both sexes spent proportionally more time in blue and green zones and less time in red zones, with no sex differences observed. This indicates a convergent pattern of immediate color choice between sexes at this stage. This cross-sex convergent choice pattern may reflect similar short-term visual-environment requirements between sexes. This study provides descriptive baseline data on immediate color choice, which can serve as a reference for subsequent investigations into long-term stable color preferences in this species. The sex-separated testing approach also offers a methodological reference for similar studies in other species.

Pine wilt disease is a devastating forest disease caused by Bursaphelenchus xylophilus infection. The associated bacterium Pseudomonas fluorescens and its flagellin protein have been implicated in this process, but the role of the flagellin-encoding gene fliC in pathogenesis remains unclear. Current gene knockout strategies in P. fluorescens are limited by low transformation efficiency and cumbersome procedures, which constrain functional studies of this gene. To address this methodological gap, we established a fliC knockout method based on the pT18sacB-sacB counterselection system. Short homologous arms were constructed by splice overlap extension PCR, and the knockout mutant ΔfliC was obtained through S17-1 λpir-mediated conjugation and sucrose counterselection. The mutant was verified by junction PCR, internal PCR, and sequencing. Using Pinus massoniana callus as the experimental material, we preliminarily compared the wild-type strain and the ΔfliC mutant in individual pathogenicity and in promoting complex infection by B. xylophilus. The ΔfliC mutant showed delayed symptom onset and lower disease severity than the wild type, and its ability to promote complex infection also appeared reduced. These results provide preliminary evidence that fliC contributes to symptom development in this callus assay. The established fliC knockout technique provides a methodological basis for further investigating the role of associated bacteria in pine wilt disease.

The freshwater sleeper (Odontobutis potamophilus) is a high-value freshwater fish endemic to China, farmed mainly in rice–crayfish–Odontobutis potamophilus integrated culture (RCO) and recirculating aquaculture systems (RAS). How these models differ in growth, physiological status, and feeding remains unclear. The same batch of fry was reared for three months (92 days) in six paddy fields (RCO, 3 individuals/m², no artificial feed, with access to natural food organisms and stocked crayfish) and six RAS tanks (6 individuals/m², fed Cirrhinus molitorella and pellet feed twice daily). Growth indicators were calculated from individual data of the sampled fish (n = 138 per model). Per group, 150 fish were sampled for stomach contents, 138 for morphometrics, and six for serum alanine aminotransferase (ALT), glutamic–oxaloacetic transaminase (AST), and glucose (GLU) assays; muscle nutritional composition was also determined. Relative weight gain rate (RWG) and specific growth rate in wet weight (SGRw) were significantly higher in RAS, with positive allometric growth in both models. Muscle crude protein was higher in RCO, whereas crude fat and serum ALT, AST, and GLU levels were higher in RAS, suggesting a heavier metabolic burden on the liver in RAS, which awaits confirmation with a broader panel of liver function markers. RCO stomachs contained nine food categories but had a 38% vacuity rate, whereas RAS fish consumed only C. molitorella (86% occurrence, 14% vacuity). Because stocking density and feeding regimen differed simultaneously between the two models, the observed differences reflect the overall effects of each culture model rather than the effect of the rearing system alone. These findings reveal a growth-metabolism trade-off between the two culture models as currently practiced: RAS produced faster growth accompanied by higher serum transaminase levels and body fat, whereas RCO maintained lower metabolic markers with slower growth. Moderate supplementary feeding in RCO and dietary diversification in RAS may reconcile yield and fish health.