Co-Cultivation with Eichhornia crassipes Enhances Growth and Ovarian Development of Micropterus salmoides

The growth and development of aquaculture organisms are significantly influenced by environmental variations shaped by different aquaculture systems. In this study, a 90-day controlled experiment was conducted to compare two pond culture setups for largemouth bass: with water hyacinth co-planted (FM group) and without (M group). As this experiment progressed, the FM group exhibited significantly superior water quality (p < 0.05) compared to the M group across multiple parameters, including total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH₃-N), dissolved oxygen (DO) and transparency, among which, the difference in transparency was especially evident (p < 0.001). Subsequently, by 90 days, the fish body weight, condition factor, and gonadosomatic index (GSI) were significantly higher in the FM group than in the M group, with the GSI difference being particularly pronounced (p < 0.001). While the GSI of M group fishes ranged exclusively from 0.01 to 0.02 (M1), the FM group displayed a much-expanded GSI range of 0.01–0.06, with 21.4% at 0.01–0.02 (FM1), 48.1% at 0.02–0.03 (FM2), and 30.5% at 0.03–0.06 (FM3). Accordingly, omics analyses of ovarian tissues were conducted between the control (M1) and the high-performing groups (FM2 and FM3). The analyses identified significant enrichment of the glycerophospholipid metabolic pathway and a marked upregulation of the Mettl3 gene (log2FC = 12.59) in the FM2 and FM3 than the M1 group, and both the pathway and the Mettl3 gene were actively involved in growth, reproductive processes, and oocyte maturation. Given that water transparency was the most markedly improved parameter, our results indicate that it may be a key driver in upregulating ovarian glycerophospholipid metabolism and Mettl3 expression in largemouth bass, thereby promoting better growth and ovarian development.