Effects of Two Farming Models on the Biochemical Composition and Response to Low Temperature Stress of Haliotis discus hannai

Abstract

The Pacific abalone (Haliotis discus hannai) is naturally distributed in the Bohai Sea and Yellow Sea. In China, the Pacific abalone is an important living marine resource. Over the past 40 years, the abalone industry has gradually developed from wild harvesting to aquaculture. Currently, the main cultivation method is long-line culture, especially north-south relay aquaculture. The north-south relay involves transporting abalone cultivated in the East China Sea to the Yellow Sea and Bohai Sea over summer, to avoid extreme temperature stress. Due to the consistent favorable temperatures, this method achieves high survival with a shortened cultivation cycle. The rapid development of this efficient cultivation model has supported a substantial increase in domestic abalone production, exceeding 200 000 tons in 2020. However, the north-south relay aquaculture has several deficiencies, such as a large influx of abalone being supplied to the market over a very limited period with a homogenized flavor. This has led to a sharp decline in price. Abalone grow slowly in the bottom-sowing model in northern waters, however, the quality exceeds that of north-south relay cultured abalone. The optimum growing temperature of Pacific abalone is 10~22 ℃. Bottom-sowing cultivation in the northern waters has a lower seawater temperature, occasionally below 0 ℃. In addition, in long-term north-south relay cultivation, abalone are always in a suitable water temperature environment, reducing the low temperature tolerance of abalone. The increasing investment in recent years in marine ecological protection (such as marine pastures, habitat restoration and abalone habitat creation) and the technological breakthroughs in the cultivation of low-temperature resistant seedlings has enabled the optimization of bottom-sowing culture, reducing many issues, such as high mortality while overwintering, which has been partially solved. However, the impact of both cultivation methods on the nutrient contents and the physiological index of abalone is rarely reported. In this study, the north-south relay and the northern bottom-sowing abalone cultures were investigated. The total sugar, protein, total organic matter, and amino acid content characterized the nutritional value of individuals from both culture methods. The oxygen consumption rate and heart rate identified their low temperature tolerance. We explore the differences in body composition and physiological mechanisms in response to low temperature stress using specimens from both farming methods. The results showed that the total sugar content of the bottom-sowing culture individuals was (3.20±0.00)%, the total organic matter was (27.60±3.70)%, and the essential amino acid content was (4.19±0.09)%, which were significantly higher than those in the individuals from the north-south relay culture (P 0.05). At 24 ℃, the heart rates of bottom-sown and relay-cultured abalone did not vary significantly, with (45.05±6.79) and (46.95±5.01) BPM, respectively (P > 0.05). In low temperature, the heart rate of the bottom-sown abalone was (12.82±1.72) BPM, and the heart rate of the relay-cultured abalone was (18.11±2.79) BPM, statistically differing significantly (P < 0.05). The results indicate variation in the abalone responses to external low temperature stress between individuals from the different farming models. The low heart rate level in low temperature conditions indicates a low metabolic level, which can reduce energy consumption, improving survival in the low temperature stress of a northern winter. Studies have revealed different farming models can significantly affect the nutritional value of abalone and the physiological responses to low temperature stress. Abalone cultured by bottom-sowing have higher nutritional value and a low temperature tolerance. In addition, abalone heart rate is a highly sensitive indicator for studying physiological responses to low temperature stress in abalone and other shellfish.

Keywords

• haliotis discus hannai
• low temperature stress
• heart rate
• nutrients
• bottom sowing farming