Reduced Hypoxia Tolerance and Altered Gill Morphology at Elevated Temperatures May Limit the Survival of Tilapia (GIFT, Oreochromis niloticus) under Global Warming

Abstract

Nile tilapia (Oreochromis niloticus) is one of the most important food fishes in global aquaculture. The optimal rearing temperature for Nile tilapia is 27–30 °C; however, in some Asian breeding areas, such as south China, water temperatures in summer frequently exceed 35 °C for several days. Potential effects of long-term exposure to high temperatures on the survival and metabolism of tilapia are unclear. In this study, genetically improved farmed tilapia, age six weeks, were exposed to water temperatures of 28, 32, and 36 °C for 15 weeks. Mean survival rates and tolerance to hypoxia were significantly reduced, and respiratory rates were increased in fish reared at 36 °C, compared to the 28 and 32 °C treatments (p < 0.05). Partial temperature compensation for routine metabolic rates was observed after 15 weeks at 36 °C. Gill morphology changes in the 36 °C treatment included curling of the lamellae and hyperplasia of the filament end, which became more pronounced after acute hypoxia (0.2 mg/L O2). Transcriptomics demonstrated that expression of numerous genes related to aerobic metabolism was altered in the 36 °C treatment, including down-regulation of nine genes of the tricarboxylic acid cycle. In summary, high temperature affected tilapia gill morphology, reduced hypoxia tolerance, and inhibited aerobic metabolism, thus ultimately threatening tilapia viability and survival.

Morphometric and Enzymatic Changes in Gills of Rainbow Trout after Exposure to Elevated Temperature—Indications for Gill Remodeling

“…In the Hoven’s carp ( Leptobarbus hoevenii ), a 20-d lasting temperature increase for 4 °C over the optimum decreases the gill epithelial thickness and changes the size of the secondary lamellae [ 6 ]. In tilapia ( Oreochromis niloticus ), a 15-week long exposure to water temperatures 8 °C over the optimum decreases the width of the secondary lamellae and causes the swelling of their terminal areas [ 7 ]. In a grouper ( Epinephelus ) hybrid, gill secondary lamella thickness increases in the lower and upper suboptimal temperature range [ 8 ].…”

Genetics and Biotechnology—The Section Editor-in-Chief’s View

“…Nile tilapia Oreochromis niloticus is often produced under unfavorably high temperatures. Zhou et al [15] exposed six-week-old juveniles to water temperatures of 28, 32, and 36 • C for 15 weeks, observing that high temperatures affected tilapia gill morphology, reduced hypoxia tolerance, and inhibited aerobic metabolism, ultimately threatening viability and survival, with transcriptional data showing the metabolic pathways that mediate these outcomes. A limited supply of fish meal has driven development of feeds using soybean meal, which is not well utilized by some cultured species.…”