Mannan oligosaccharide (MOS), a prebiotic derived from yeast cell walls, has been shown to enhance growth performance and health status in various aquatic species. As an exogenous antigen adjuvant, MOS modulates T-cell-mediated immune responses, thereby improving immune function and suppressing excessive inflammatory reactions. This study aimed to evaluate the effects of dietary MOS supplementation on growth performance, serum biochemical parameters, muscle composition, digestive enzyme activity, antioxidant and immune status, and the mTOR signaling pathway in juvenile GIFT tilapia (Oreochromis niloticus). Juveniles (initial body weight: 16.17 ± 1.32 g) were randomly assigned to six treatment groups (three replicate tanks per group) and fed diets supplemented with MOS at 0, 0.2%, 0.4%, 0.6%, 0.8%, and 1% (equivalent to 0, 2, 4, 6, 8, and 10 g/kg of diet, respectively) for 60 days. Compared with the control group, fish fed MOS-supplemented diets exhibited significantly higher (p < 0.05) weight gain rates, specific growth rates, and protein efficiency ratios, along with a significantly lower (p < 0.05) feed conversion ratio. Serum albumin, high-density lipoprotein, and lysozyme levels were significantly increased (p < 0.05), whereas triglycerides, low-density lipoprotein, aspartate aminotransferase, and alanine aminotransferase levels were significantly decreased (p < 0.05). In the liver, head kidney, and spleen, the expression of pro-inflammatory genes (tumor necrosis factor α, interleukin 1β, interleukin 6, interleukin 8, and interferon γ) was significantly downregulated (p < 0.05), while the expression of antioxidant and protective genes (superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, nuclear factor erythroid 2-related factor 2, lysozyme, alkaline phosphatase, interleukin-10, transforming growth factor β, and heat shock protein 70) as well as mTOR signaling pathway-related genes (mammalian target of rapamycin, akt protein kinase B, phosphatidylinositol 3 kinase, and ribosomal protein S6 kinase polypeptide 1) was significantly upregulated (p < 0.05). Overall, MOS positively affects tilapia’s growth, health, and immunity, with 0.60% identified as the optimal dietary level based on growth performance.

Trilobites exhibiting injuries are ideal palaeontological archives for Palaeozoic predator-prey interactions. However, the current methods for diagnosing trilobite injuries primarily depend on the various morphological features at the edges of the injured exoskeleton, without evaluating the process and timing of morphological changes. Here we performed an amputation experiment utilizing the extant horseshoe crab as a proxy of trilobites to study the morphological changes after injury. The results show that: the wound closure was accomplished by forming hemolymph clotting on the wound surface in a short time. And then, a thin cuticle layer was growing on the inner side of wounded exoskeleton, with the retention of a sharp outline of the wound. Particularly, the newly-formed exoskeleton only regenerates and modifies the shape of the wound subsequent to moulting. After rechecking 409 abnormal trilobites documented in the published literature, we recognized that the injuries with sharp exoskeleton edge are very rare in the fossil record, and 95% of injured trilobites with clearly identifiable scars had undergone at least one subsequent ecdysis. This indicates that the majority of the injuries were not identified, as the sharp wounds were indistinguishable from post-mortem breakage. These unidentified injuries may encompass successful predation events, lethal injuries, and damage incurred during the adult stage, none of which exhibit signs of moulting. Although we are currently unable to deal with this recognition bias, through injury experiments on living arthropods, our understanding of the damage types and repair processes of trilobites will be further enriched.