Effect of LED light quality on respiratory metabolism and activities of related enzymes of Haliotis discus hannai

Abstract

Oxygen consumption and ammonia excretion rates of abalone (Haliotis discus hannai) of differing sizes (wet weight 63.74±8.49g, 17.49±3.20g, and 3.52±0.94g) were evaluated under five different light emitting diode (LED) conditions (red, orange, purple, green, and blue light) and in dark and natural light environments. The weight-specific oxygen consumption/ammonia excretion rates decreased significantly with increasing body weight, and these relationships could be expressed by the exponential equations R=aWb and E=aWb (P<0.05), respectively. The oxygen consumption/ammonia excretion rates of abalone in the red light, orange light, and dark environment treatments were lower than those in the green, blue, natural, and purple light treatments, and the highest rates (3.27mgg−1 h−1/187μgg −1 h −1) occurred in the purple light treatment (P<0.05). The O/N ratio exceeded 10 in all light quality groups, indicating that the energy requirements were met by carbohydrate and fat. In another experiment, the effects of different light qualities on the activities of hexokinase (HK), pyruvate kinase (PK), superoxide dismutase (SOD), and catalase (CAT) in juvenile abalone (wet weight 17.49±3.20g) were investigated at 0.5, 1, 3, 6, 12, 24, and 72h of light exposure. HK and PK activities in the green, purple, blue, and natural light groups were significantly higher than those in the red light, orange light, and dark environment (P<0.05). SOD activity increased immediately when the abalones were placed in green, purple, blue, and natural light, then decreased gradually and returned to its original level. CAT activity did not increase until 12h and was higher in the green, purple, blue, and natural light groups than in the red light, orange light, and dark environment (P<0.05). These results suggest that more carbohydrates were provided and utilized by the glycolytic cycle when the abalones were exposed to adverse light conditions. Therefore, the selection of appropriate light conditions (red and orange light) and the control of metabolic waste ammonia will have a significant impact on high-intensity aquaculture in recirculating cultivation systems. Statement of relevanceThe disk abalone Haliotis discus hannai is an economically important shellfish in China, with demand growing for this high-protein and low-fat seafood. In 2012, 90 694t of H. d. hannai were harvested from aquacultural sources, but supply cannot currently meet consumer demand. In recent years, the natural habitat of H. d. hannai has declined as a result of overfishing, marine reclamation, water pollution, among others, leading to a sharp decrease in the numbers of H. d. hannai in the wild. Thus, the development of an aquacultural system for farming H. d. hannai, as well as for its protection in the wild, are a focus of current research.Light, including photoperiod, quality and intensity, is one of the key environmental factors influencing the growth, culture and survival of aquatic organisms. Over evolutionary time, organisms have evolved both physiological and behavioral mechanisms that enable them to adapt to diurnal fluctuations in light. This is particularly relevant to coastal aquatic environments, where various phytoplanktonic species and dissolved organic matter in the water can absorb or scatter blue light, converting the light quality of transmitted light from blue-green to green-orange. Blue light (470nm) has the strongest penetrability in clean seawater, whereas red light and ultraviolet (UV) are quickly absorbed in clean seawater. In its natural environment, H. d. hannai is mostly distributed in shallow inshore waters at a depth of less than 10m. Such waters are also inhabited by dense populations of phytoplankton and contain high levels of dissolved organic matter, which both diminish the transmission capacity of light, particularly of blue light, and this can result in an extended range of red and orange light, rather than blue light, in the water.In Chinese traditional abalone aquaculture, a sunshade net is usually used because of the photophobic nature of abalone. In particular, the aquaculturist usually provides a darkened setting for adult abalones to increase their food intake rate, facilitate their growth and promote gonadal development. For abalones in their natural environment, the light quality in the water area is relatively stable, suggesting that there is a key regulative effect of light quality on their growth and development.The aim of the present study was to evaluate the effects of different LED light qualities on the respiratory metabolism and physiological response of abalones by measuring oxygen consumption rate, ammonia excretion rate, glycolytic enzyme activity, and antioxidant defense. Our results may be used to optimize the light conditions for optimal growth and survival of abalones and to provide basic theory for regulation and control of light conditions in closed recirculating aquaculture systems in general.