LOW-FISHMEAL AND HIGH-FAT DIET SUPPLEMENT WITH SOYBEAN LECITHIN ON GROWTH, SERUM BIOCHEMICAL INDEXES AND INTESTINAL FLORA OF RICE FIELD EEL (MONOPTERUS ALBUS)

This feeding trial aimed to investigate the effects of soybean lecithin on the growth, serum biochemical indexes and intestinal flora of rice field eel (Monopterus albus) when fed a low-fishmeal and high-fat diet. This research provides a valuable insight into thedevelopment of low-fishmeal feed for M. albus. Eels with an initial body weight of (20.03±0.01) g were selected as the research object. The control group was fed a diet consisting of 42% fish meal, 22% soybean meal and 6% crude fat, while the experimental group received a diet containing 22% fish meal, 52% soybean meal and 9% crude fat to represent the low fish meal and high fat group. Additionally, 1% and 2% soybean lecithin were added to the experimental group. The feeding trial spanned 56d and was conducted in outdoor ponds using cage culture. Alligator weed were laid in the cages and provided as daily feed, comprising 3%—5% of the weight of M. albus. The results showed as follows: (1) compared with the normal fish meal group, the decreased weight gain rate of rice field eel was observed in the low fish meal and high fat group (P<0.05), coupled with the significantly increased value in the feed conversion ratio and hepatosomatic index (P<0.05). Notably, 2% soybean lecithin supplementation contributed to a higher weight gain rate and lower values in the feed conversion ratio and hepatosomatic index of rice field eel compared to the low-fishmeal and high-fat group (P<0.05). (2) Compared with the control group, the levels of serum triglyceride, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, blood ammonia, urea nitrogen, aspartate aminotransferase, alanine aminotransferase, acid phosphatase and immunoglobulin M were significantly increased in rice field eel fed low fish meal and high fat diet (P<0.05). Conversely, the levels of alkaline phosphatase were significantly decreased (P<0.05). The addition of 2% soybean lecithin significantly increased the levels of serum high density lipoprotein and alkaline phosphatase (P<0.05), while levels of serum low density lipoprotein, blood ammonia, urea nitrogen, aspartate aminotransferase, alanine aminotransferase, acid phosphatase and immunoglobulin M were significantly decreased (P<0.05); (3) Compared with the control group, the villus height and number of goblet cells in the hind-gut of the low fish meal and high fat group were significantly decreased (P<0.05), however, these parameters improved after adding 2% soybean lecithin. (4) Compared with the control group, the low fish meal and high-fat group displayed a higher relative abundance of Acinetobacter and Kocuriacould in the intestinal flora. After the addition of 2% soybean lecithin, the microbial community of the rice field eel increased significantly (P<0.05). Furthermore, the relative abundance of intestinal Rhodobacter increased significantly, while Acinetobacter and Kocuria were significantly inhibited (P<0.05). In conclusion, under the conditions of this experiment, it can be inferred that 2% soybean lecithin promote fat metabolism, improve the immune performance of the body, repair the intestinal tissue structure and maintain the homeostasis of the flora. Consequently, it alleviates the negative effects of low-fishmeal and high-fat diet on the growth of rice field eel.