Abstract
In this study, the effects of different salinity levels (9, 12, 15, 18, 21, 24, 27, 30, and 33) on the growth performance, body composition, antioxidant indexes of Perinereis aibuhitensis (initial average mass, 20.4 ± 0.3 mg) and total nitrogen in the substrate were investigated. The survival rate, specific growth rate, feed coefficient, and protein efficiency ratio under different salinity levels were measured. The results showed that the survival rate of P. aibuhitensis at the salinity level of 9 was significantly lower than that of P. aibuhitensis at other salinity levels (P 0.05). On the basis of quadratic polynomial fitting of the relationship between salinity levels and the specific growth rate, feed coefficient, and protein efficiency ratio, it was concluded that 25.36 - 25.9 is the most suitable salinity range for the growth performance of P. aibuhitensis. The main body composition (moisture, crude fat, crude protein, and ash content) was measured at different salinity levels. The results indicated that, with the increase in salinity, the moisture content of P. aibuhitensis decreased gradually; in contrast, the ash content increased gradually, as the salinity level increased. However, in the salinity range of 18 to 33, the difference in ash content was not significant (P > 0.05). Salinity had a significant influence on the crude protein content (P < 0.05), while it had no significant influence on crude body fat. Crude protein showed an increasing trend with the salinity increasing from 9 to 24, and decreased with the salinity increasing from 24 to 33. Antioxidant indexes such as superoxide dismutase, catalase, glutathione, and malondialdehyde (MDA) were analyzed, showing that in vivo MDA content was as low as the antioxidant activity at the salinity level of 24; this means low in vivo contents of active oxygen free radicals and excellent growth performance. This conclusion is consistent with that for other growth indexes. The total nitrogen content of the substrate in which the P. aibuhitensis specimens were cultured for 60 days was higher than the total nitrogen in the soil. With an increase in salinity, the total nitrogen content first decreased and then increased, and the lowest value was observed at the salinity level of about 24.
Highlights
Salinity is a non-nutritional factor necessary for the survival and growth of aquatic organisms, and it has an impact on various physiological activities such as growth and metabolism [1]
The results showed that the survival rate of P. aibuhitensis at the salinity level of 9 was significantly lower than that of P. aibuhitensis at other salinity levels (P < 0.05)
A previous study has shown that the salinity levels suitable for the growth of P. aibuhitensis have a broad range [13]
Summary
Salinity is a non-nutritional factor necessary for the survival and growth of aquatic organisms, and it has an impact on various physiological activities such as growth and metabolism [1]. Salinity affects the digestion and absorption of food by changing the activity of the digestive enzymes, affecting the weight gain rate and specific growth rate of aquatic organisms. It is important to choose the most suitable salinity range for the survival and growth of aquatic organisms [2]. Body composition of aquatic organisms is composed of water, carbohydrates, proteins, fat, ash, etc. Previous studies have reported no significant differences in the effects of salinity on the body composition of fishes such as Paralichthys olivaceus [3] and Platichthys stellatus [4]. Other studies have indicated that appropriate salinity levels helped to save the osmotic pressure energy in fish, resulting in good growth performance and high protein and fat content [5]. A previous study on Sebastes schlegeli [6] showed that the activities of SOD and CAT in the blood increase gradually with the decrease trend; another study on the Nibea japonica [7] indicated that the activities of SOD and CAT in the liver, kidney, and muscle at different salinities showed no significant differences (P > 0.05), which may be related to the different salinity adaptations of different organisms
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