{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,26]],"date-time":"2026-06-26T17:33:56Z","timestamp":1782495236370,"version":"3.54.5"},"reference-count":37,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2023,2,2]],"date-time":"2023-02-02T00:00:00Z","timestamp":1675296000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"Introduction<\/jats:title>Temporal elevation of water temperature positively affects immune activity and disease resistance in poikilothermic teleost fish. The ayu, Plecoglossus altivelis<\/jats:italic>, an important fish species for Japanese freshwater fisheries, is usually produced under higher water temperatures than the natural conditions to facilitate rapid growth. However, it has been reported that rearing fish at higher water temperatures inhibits the development of the thymus, suggesting that resistance to infectious diseases is reduced in ayu reared at higher water temperatures. Here, we show that decreased resistance to bacterial cold-water disease and excessive inflammatory responses occurred in ayu reared at 22\u00b0C compared with those reared at lower temperatures.<\/jats:p><\/jats:sec>Methods<\/jats:title>Ayu larvae were reared at 12\u00b0C, 15\u00b0C and 22\u00b0C for 77 days and fed 3% of their body weight. Thymus index and condition factor was calculated after the fish rearing. Then, ayu reared at the different temperatures were challenged with Flavobacterium psychrophilum and the fish were sampled for histopathology and gene expression analyses. Further, the fish were vaccinated with formalin-killed F. psychrophilum and continuously reared at the three different water temperatures. Serum antibody titer was determined by ELISA and cumulative mortality in each group was recorded after the bacterial challenge.<\/jats:p><\/jats:sec>Results<\/jats:title>Ayu reared at 22\u00b0C showed a significantly lower thymus index and higher condition factor than those reared at lower temperatures. Infiltrated leukocytes and many melanin pigments were frequently observed in the adipose tissues and spleens of ayu reared at 22\u00b0C, respectively, but not in those reared at 12\u00b0C. The gene expression levels of inflammatory cytokines such as IL-1\u03b2, IL-8 and TNF\u03b1 in the spleen were significantly higher in the 22\u00b0C group than in the 12\u00b0C group. The cumulative survival rate after challenge with Flavobacterium psychrophilum<\/jats:italic> was 51.7%, 40.0% and 13.3% in the 12\u00b0C, 15\u00b0C and 22\u00b0C groups, respectively. The relative percent survival values of vaccinated fish reared at 15\u00b0C and 22\u00b0C groups were lower than those reared at 12\u00b0C. Moreover, the specific antibody titer of the vaccinated fish was the lowest in the 22\u00b0C group and the highest in the 12\u00b0C group. <\/jats:p><\/jats:sec>Discussion<\/jats:title>These results suggest that rearing the fish under high water temperature causes excessive inflammatory responses similar to metabolic inflammation in human obesity, resulting in a decrease of disease resistance. In addition, thymic involution induced by higher water temperature probably leads the poor response to vaccination. The present study provides insights into the physiological and immunological changes of fish under global warming.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fimmu.2023.1101491","type":"journal-article","created":{"date-parts":[[2023,2,2]],"date-time":"2023-02-02T05:20:08Z","timestamp":1675315208000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":9,"title":["Decreased resistance to bacterial cold-water disease and excessive inflammatory response in ayu (Plecoglossus altivelis) reared at high water temperature"],"prefix":"10.3389","volume":"14","author":[{"given":"Goshi","family":"Kato","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hayato","family":"Nakajima","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kyuma","family":"Suzuki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuhei","family":"Kanzawa","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chihaya","family":"Nakayasu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kosei","family":"Taguchi","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Osamu","family":"Kurata","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Motohiko","family":"Sano","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2023,2,2]]},"reference":[{"key":"B1","article-title":"Elevation 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