| H. discus hannai is an economically important shellfish species in China, but culture of this species has been experiencing numerous problems as the aquaculture industry develops and expands(e.g., incomplete seed development, worsening summer mortality, drastic rise of feeding costs). In traditional Chinese aquaculture, producers often use sunshade nets in aquaculture workshops to provide a relatively dark living environment for abalones. However, in the abalone’s natural environment, the light quality and cycle are subject to the seasonal rhythm and variations in concentration of suspended particles, zooplankton, and phytoplankton.Abalonesare able to survive, grow, and reproduce in the ever changing natural environment, and light may have important regulatory effects on growth and development in this setting.1. Effect of LED light quality on the phototaxisand locomotion behavior of Haliotis discus hannaiAbalones were reared in a laboratory to determine the percentage response rate, response time, average crawling speed, and the time taken to recover an upright posture under nine light-emitting diode light quality treatments(red, orange, yellow, green, cyan, blue, purple, white, and gray) and a dark environment. Animals were placed in the center of an experimental device, and the tropism of each animal was continuously monitored by video. The highest percentage response rate(80% in dark adapted abalones, 60% in light adapted abalones) was observed in the dark environment, followed by red and orange light(27 and 30% in dark adapted abalones, respectively 22 and 24% in light adapted abalones). Two induction materials(substrate and brown algae Laminaria japonica) were used to assess the effect of lightquality on the tropism of abalones, with the highest percentage response rate(76% in the L. japonica treatment, 22% in the substrate treatment) also observed in the dark environment, followed by red and orange light(both 25% in the L. japonica treatment, and 26 and 32%, respectively, in the substrate treatment). The tropism order of the abalones under dark, red, orange, and yellow light was as follows: dark > orange > red, yellow, but fewer abalones chose to stay in blue, green, cyan, and purple light. The response time(about 700 s) in the dark environment was significantly longer than for the other light quality treatments(P<0.05). Compared with the average crawling speed in the other light quality treatments, abalones were relatively slower(about 3.8 mm/s) in red and orange light, and the dark environment. The mean time required for the recovery of an upright posture in red light and the dark environment was longer than in the other light quality treatments(P<0.05), with the average recovery time reaching a maximum of 60 s in the dark environment. The results demonstrate the phototaxis and locomotion behavior of abalones, as well as confirming the necessity of a dark, orange, or red environment for their management and aquaculture.2. Light and electron microscopic study on the eye of Haliotis discus hannai InoIn the present study, the eye tissues of Haliotis discus hannai Ino were observed under the light microscope, scanning electron microscope and transmission electron microscope to further provide the histological and cytological basis for the analysis of the physiological response mechanism of abalone to light from the perspective of molecular biology. Finding shows that the eye tissues are retinal pigment epithelium, outer nuclear layer, inner segment, inner nuclear layer, melanin granules sediments and optical fibre layer from the outside to the inside. The surfaces of eye tissues are covered with papillae and the top of every papillae has one or two clusters of ciliary rings. Loose connective tissue, smooth muscle fiber and others are main components in the tissues, collagenous fibers and others distributed between the connective tissues play a key role in maintaining the flexibility and toughness of cells.3. Effects of LED light quality on the growth, metabolism, and energy budgets of Haliotis discus discusLight is one of the key environmental factors influencing the growth, development, and survival of aquatic organisms, which have evolved to be able to change their physiology and behavior to adapt to changes in light conditions. In this study, a bioenergetics approach was used to examine the effects of different LED light qualities(red, orange, blue, green light, natural light and a dark setting) on the growth and survival of the abalone Haliotis discus discus, and its physiological response mechanism under different light qualities. The results suggest that under blue or green light, the survival rate, specific growth rat, food intake, and food conversion efficiency of H. d. discus were significantly lower than in those groups under red or orange light(P<0.05). Under red or orange light, the protein content, ash, and tissue:shell ratio of H. d. discus were significantly higher than in those groups under other light qualities(P<0.05). Under red or orange light, pepsin, amylase and cellulose activity was significantly higher than those in any other light quality group(P<0.05), whereas lipase activity exhibited no significant difference among the light quality groups(P>0.05). Under blue or green light, hexokinase and pyruvate kinase activity was higher than in other groups(P<0.05). Under red or orange light, or in dark setting, succinate dehydrogenase activity was significantly higher than in any other group(P<0.05), indicating that enhanced aerobic metabolism that was conductive to the continuous crawling of H. d. discus. Under blue or green light, lactate dehydrogenase activity and lactic acid content were higher(P<0.05), suggesting enhanced anaerobic metabolism. Under blue or green light, H. d. discus lost more energy via excretion, feces and respiration than was acquired from its food; as a consequence, there was no energy available for its growth. Under red or orange light, H. d. discus acquired more energy from its food and lost less energy via excretion and feces; as a result, its assimilation efficiency(K1) and net growth efficiency(K2) were significantly higher than those of any other group(P<0.05). Therefore, we suggest that red or orange light should be used as a light source for the aquaculture of H. d. discus to reduce costs, increase the yield per water body, and improve the welfare culture of this and other species of abalone.4. Effects of light quality and intensity on the growth, survival, and metamorphosis of Haliotis discus hannai Ino larvaeThis study examined the effects of different light qualities(red, orange, white, blue, and green light) and intensities(5 μmol/m2/s, 15 μmol/m2/s, and 40 μmol/m2/s) on the hatching and metamorphosis of larva of Haliotis discus hannai Ino and the growth and survival of juveniles. It was found that under blue and green light, the hatching success rate and metamorphosis of larva were significantly higher than for any other light quality(P<0.05), and there was a decreasing trend with an increase in light intensity. Under red and orange light, the abnormality rate of trochophores in each light intensity treatment and the time required for the metamorphosis of larva were significantly higher than for any other light group(P<0.05). Both the abnormality and metamorphosis rates significantly increased with light intensity. Under white light, at an intensity of 40 μmol/m2/s, the settlement and size of larva at metamorphosis were significantly smaller than for any other light intensity(P<0.05). Under red and orange light, the SGR of juvenile abalone in each light intensity treatment was significantly lower than in any other light group(P<0.05), but no significant difference was identified(P>0.05). Therefore, by selecting blue and green light and controlling the light intensity to 5–15 μmol/m2/s during fingerling reproduction of abalone should increase the hatching success rate of larva and the yield per water body.5. Physiological metabolism of Haliotis discus hannai Ino under different light qualities and cyclesThe goal of this experiment was to examine the effects of different light qualities(red, white, blue) and cycles(12L:12D, 8L:16D, 4L:20D, 0L:24D, 16L:8D) on the survival, growth, metabolism, and antioxidant defense system of Haliotis discus hannai Ino.Under red and white light at 4L:20D, the body weight specific growth rate of abalones was significantly higher than that of the 0L:24D group(P<0.05), which was due primarily to the higher food conversion efficiency. Under red and white light at both 4L:20D and 8L:16D, the crude protein, ash, and fat contents of abalones were significantly higher than those of the blue light group(P<0.05). Under red and white light, the activities of amylase, cellulase, and pepsase increased significantly(P<0.05) with increased duration of light exposure. At 16L:8D, succinate dehydrogenase activity decreased and lactate dehydrogenase and alanine aminotransferase activity and the lactic acid content significantly rose(P<0.05) in the red and white light groups. Under blue light, reactive oxygen species and malondialdehyde content for each light cycle were significantly higher than those of the red and white groups(P<0.05), but no significant difference in content was detected between the red and white light groups(P>0.05). Under blue, white, and red light, total antioxidant capacity(T-AOC), superoxide dismutase(SOD) activity, glutathione peroxidase(GPX) activity, and reduced glutathione(GSH) content gradually rose with increased duration of light exposure. Under red light, significant differencesin these parameters were detected between the 4L:20D and 16L:8D groups(P<0.05). Under blue and white light at 16L:8D, values of T-AOC, SOD, GPX activity, and GSH content were significantly lower than those of the 12L:12D group(P<0.05). Overall, these results indicate that red light at light cycles of 4L:20D and 8L:16D is optimal for the culture and production of H. discus hannai, as these conditions promoted food intake, growth, and health maintenance as well as normal physiological metabolism of the organism. |
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