| Duckweed is a small aquatic floating plant in the Lemnaceae,with fast growth and reproduction,high biomass and wide distribution.It is rich in nutrients,simple to havest,highly tolerant,and capable of absorbing nitrogen and phosphorus.It plays an important role in the fields of environment,medicine,beauty,bioenergy,livestock and poultry diet,and is a new type of nonfood cash crop.In recent years,feed protein sources have become increasingly nervous,and duckweed has the potential to become a high lysine feed protein source,and is expected to develop new duckweed feed.This study first examined the distribution of duckweed in three provinces/cities in the lower reaches of the Yangtze River,and classified the collected duckweed germplasm resources to determine their status in the classification system.Simultaneously,a duckweed strain in the genus Spirodela was used as a research material,mixed with a commonly used commercial feed in different propotions,and feed to juvenile Nile tilapia(Oreochromis niloticus)for 60 days.A new feed recipe containing duckweed was formulated in order to develop a new and healthy feed for tilapia.The main research results of this paper are as follows:(1)A total of 25 living populations of duckweeds were collected from 13 cities and counties in Jiangsu,Anhui,and Shanghai in the lower reaches of the Yangtze River.Only one community was composed of a single species,the rest consisted of two or more.A total of 90 strains were identified,sterilized and stored in the germplasm bank.According to morphological identification and molecular biology methods to build phylogenetic trees analysis found,there are 4 genera and 6 species of duckweeds in the lower reaches of the Yangtze River.They are L.aequinoctialis,L.turionifera,L.gibba,S.polyrhiza,Lan.punctata,W.globosa.Among them,Lemna is the most commonly distributed,followed by Spirodela,the least distributed genera are Landoltia and Wolffia.Duckweed germplasm in the lower reaches of the Yangtze River is rich in genetic diversity,and rpS16 is more diverse than AtpF-AtpH,of which Lemna is the most diverse genus.(2)Substitution of 0%,10%,15%,20%,25%and 30%of the traditional feed by duckweed DW4701 dried powder improved the growth of tilapia juveniles to a certain extent compared with the Tongwei feed group in terms of body mass,CF,WGR,SGR and digestive enzyme activity.When the duckweed dried powder was added by 20%,the feeding effects were the best.The weight,WGR,CF,VSI,HSI,SGR increased by 18.42%,19.61%,20.37%,17.33%,395.00%and 6.20%,respectively,compared to the Tongwei feed.Amylase activity in the stomach,intestine,liver and pancreas increased by 46.67%,81.81%and 20.19%,respectively.Protease activity increased by 35.91%,150.56%and 127.87%,respectively.Lipase activity increased by 5.02%,238.22%and 97.33%in the stomach,intestine,liver and pancreas.(3)New feed with different ratios of duckweed DW4701 dried powder have certain effects on tilapia’s body mass,CF,WGR,SGR and digestive enzyme activity.When duckweed dried powder was added by 25%,the feeding effect was the best.Body weight,WGR,CF,VSI,HSI,and SGR increased by 34.74%,36.99%,25.93,11.03%,360.00%and 10.68%,respectively,compared with the Tongwei feed group.Amylase activity in the stomach,intestine,liver and pancreas increased by 20.00%,100.00%and 40.48%,respectively.Protease activity increased by 12.85%,157.56%and 68.15%,respectively.Lipase activity increased by 43,25%,212.89%and 102.08%,respectively.Taking all indicators into account,the formula with 25%duckweed dried powder has the best feeding effects.In summary,duckweed has great application prospects as a plant protein source,and is worthy of in-depth study.It is of great significance to identify and further develop and utilize duckweed germplasm resources. |
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