Effect of Trap Space Layout on Trapped Number of Spodoptera litura in Tobacco Field

Fei DAI Xiquan LI Xingping YANG Hao QIN Rui ZUO

AbstractChinese sucker (Myxocyprinus asiatius) is a national secondary protection animal in China, as well as unique economic fish in China having extremely important scientific research value and edible value. With the aggravation of water pollution and the massive construction of water conservancy and hydropower projects, the natural spawning ground of Chinese sucker has been seriously damaged. The current number of wild resources has decreased sharply, and the decreasing trend is continuing. This paper summarized the current resource status and monitoring and assessment methods of Chinese suckers, and put forward the research prospect, so as to provide theoretical reference and technical support for resource protection and development and utilization of Chinese sucker in China.

Key wordsMyxocyprinus asiatius; Resource status; Monitoring and assessment

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Received: July 22, 2018Accepted: October 19, 2018

Supported by College Students Practice Innovation Training Program of Jiangsu Province (201312806015Y); Research Project of Jiangsu Agrianimal Husbandry Vocational College (NSFYB1408); Qing Lan Project for Talent Training in Colleges and Universities in Jiangsu Province (00000216014).

Jiansheng YE (1981-), male, P. R. China, master, associate professor, devoted to research about economic aquaculture animal ecology and nutriology.

*Corresponding author. Email: yejianshengye@sohu.com.

Chinese sucker (Myxocyprinus asiatius) belongs to Catostomidae in Cypriniformes, and is named for its cheek color which looks like rouge used by ancient Chinese women. Chinese sucker has only one genus and one variety in China, and is a kind of Chinas secondclass protected animal. It has extremely important scientific research value in fish phylogenetic classification and animal geography research, and is mainly distributed in the Yangtze River and the Minjiang River. Chinese sucker now has the largest number in the upper reaches of the Yangtze River, and almost extinct in the Minjiang River, and its spawning grounds are the upstream parts of the Yangtze River such as the Jinsha River, Minjiang River and Jialing River. In the past 40 years of the reform and opening up, with the rapid development of Chinas economy and society, environmental pollution has been aggravated, and overfishing has been continuing despite repeated prohibitions, resulting in a continuous decline in the level of biodiversity in natural waters. In addition, reasons including Yangtze River waterway construction, dam construction and hydropower station construction have seriously damaged the natural spawning ground environment of Chinese sucker, and combined with its unfavorable factors such as long development cycle and low fertility, a serious decline in the number of wild populations of Chinese suckers is resulted［1-2］. In view of the above reasons, it is urgent to protect Chinese sucker resources.

The artificial breeding and fry rearing of Chinese sucker［3-7］ succeeded in the 1990s, which provides technical support for the resource conservation and industrialization development of Chinese sucker. In recent years, most researches on Chinese sucker at home have focused on artificial breeding［8-9］ and nutritional needs［10-18］, while research on resource conservation and monitoring and evaluation of Chinese sucker has not been systematically deepened.

Current Status of Chinese Sucker Resources

Carrying out artificial discharge of Chinese sucker is the most effective way to avoid further reduction of the amount of Chinese sucker resources in natural waters and accelerate the proliferation and recovery of their resources［19］. The reason for the continuous decline in the amount of Chinese sucker resources is mainly due to its low fertility and long development time and human factors such as overfishing, water pollution, largescale water conservancy projects and excessive excavation of river sand［20］. Zhang et al.［21］ speculated that the spawning grounds of Chinese sucker are mainly located in the Hejiang-Yibin section of the upper reaches of the Yangtze River, and the Jialing River and the Minjiang River. Chinese sucker mainly lives in the upper reaches of the Yangtze River, and there is no habit of breeding migration in its life history; some individuals that live in the lower reaches of the Chuanjiang River or Chinese sucker juveniles hatched here may drift downstream to the middle and lower reaches of the Yangtze River to grow and develop, and return to the upstream and stay there when grown up, no longer returning downstream.

With the rapid development of industry and agriculture along the Yangtze River in China, the pollution situation in the waters is also intensifying, and various organic poisons, heavy metals, toxic microorganisms and hypoxia in the water all have an impact on the metabolism and physiological functions of the fish. When the water has salinity <3 and nitrogen and phosphorus concentration better than water quality standard grade III, Chinese sucker has relatively stable physiological response and a survival rate of 100%. When the nitrogen and phosphorus concentration falls into water quality grade V, Chinese sucker begins to die［22］. Pan et al.［23］ showed through toxicological tests that organic poisons and heavy metals have a stress effect on Chinese sucker, and it is speculated that low dissolved oxygen and toxic microorganisms are key ecological factors that determine the survival of Chinese sucker. Yan et al.［24］ showed that juvenile Chinese sucker had low tolerance to Pb in water, and under chronic exposure to water Pb, the activity glutathione Stransferase (GST) in liver, kidney and gill increased with the increase of Pb concentration, and the resting metabolic rate and the mitochondrial metabolic rate of the liver also increased with the increase of Pb concentration; and glycogen content in the liver decreased with the increase of Pb exposure concentration, and the specific growth rate gradually decreased with the Pb exposure concentration increasing. Chen et al.［25］ showed that Cd2+ can induce apoptosis of blood cells in Chinese suckers. Blood cells of Chinese sucker showed typical apoptosis characteristics of cell rounding, nuclear rounding, nuclear marginalization, and formation of apoptotic bodies. And after 1 h of stress with 0.01 mmol/L Cd2+, apoptosisinducing effect was observed, and the apoptosis rate increased with the increase of Cd2+ concentration and the prolongation of action time.

In order to prevent and control diseases in aquaculture production, the application rates of pesticides such as copper sulfate, pyrethroids and triazophos are increasing, which often causes poisoning of farmed fish due to improper use of drugs and pesticide residues. Chen et al.［26］ showed that the safe concentrations of copper sulfate, formaldehyde, fenvalerate, triazophos and trichlorfon were 0.57, 27.2, 0.009, 0.013 and 6.9 mg/L, respectively. Scientific research provides a theoretical basis for breeding and adult fish production.

In addition, as the urbanization along the Yangtze River continues to accelerate, port construction, waterway construction, bridge construction, ship navigation and sand mining on the Yangtze River are becoming more frequent, and the resulting noise pollution is increasing. Hearing ability is an important survival skill for fish. Underwater noise can not only cause hearing loss in fish, but also a temporary threshold shift, or even a permanent threshold shift［27］. The highintensity noise generated by underwater blasting and piling in hydraulic engineering can directly cause damage to tissues and organs of fish, and even directly cause death［28］; and on the other hand, it will cause other nonhearing effects of fish, for example, noise exposure can lead to increased stress levels［29］, changes in fish behavior and even fish reproduction failure［30］. Liu et al.［31］ studied the auditory threshold of Chinese sucker, and used the auditory brainstem response to record brief tone auditory evoked potential with an electrode inserted under the skin of Chinese sucker. The results showed that the audiogram of Chinese sucker showed a "U" shape, with higher threshold in the high frequency and low frequency regions and lower IF threshold, belonging to a typical animal hearing curve. Chinese sucker has an audible frequency range of 100-5 000 Hz and a high sensitivity to 100-2 000 Hz. Its most sensitive frequency is 800 Hz and the hearing threshold is approximately 69.8 dB. Therefore, the auditory threshold of Chinese sucker has important research significance for the protection of Chinese sucker resources and can be used to evaluate the impact of noise on Chinese sucker.

Mornitoring and Assessment

Morphological assessment

In order to protect and restore Chinese sucker resources, national and local provinces and cities along the Yangtze River have adopted protective measures such as artificial proliferation and release. Due to inbreeding, bait abundance and composition, drastic changes in habitats, etc., traits may decline in farmed populations, resulting in morphological differences between farmed and wild populations［22-33］. In order to scientifically evaluate the effects of artificial proliferation and release measures on the recovery of Chinese sucker resources, it is first necessary to accurately distinguish between wild and artificial released groups. Wu et al.［34］ performed morphological difference analysis on three artificiallybred Chinese sucker populations from Sichuan Fisheries Research Institute (SCC), Yibin Rare Aquatic Animal Research Institute (YBC) and Chongqing Wanzhou Fisheries Research Institute (WZC) and three wild populations from the ranges of Luzhou (LZW), Mudong (MDW) and Wanzhou (WZW). Among them, WZC and YBC were similar in morphology, and were distinct from SCC in terms of dorsal fin length/body length, lobe length of caudal fin/body length, and eye diameter/body length; WZW was similar to MDW in morphology, and was distinct from LZW in tail height behind anal fin base/body length, snout length/body length, head length/body length, head length behind eyes/body length and height of head/body length; and WZW sample was morphologically similar with SCC sample, while MDW was morphologically similar with WZC and YBC samples. In conclusion, no obvious morphological differences were found between the hatcherybreeding and wildcaught aggregates of Chinese sucker, which might be related to the fact that most individuals are not tagged when artificially released, which makes distinguishing cultured populations from wild populations difficult.

Therefore, in order to accurately distinguish released Chinese sucker population, it is necessary to strengthen the research of tagging release technology and combine it with molecular biological methods such as genetic markers.

Molecular biology assessment

Artificial proliferation of Chinese sucker by releasing should not only increase the population, but also should ensure that the genetic characteristics of the wild germplasm resources are not interfered and should not affect the natural ecosystem of waters where Chinese sucker is to be released. Therefore, it is necessary to do a good job of monitoring and evaluation of artificial discharge and discharge management. Yang et al.［35］ believed that establishment of a highly polymorphic microsatellite DNA enrichment library for Chinese sucker and systematic development of microsatellite primers unique to Chinese sucker have a guiding significance to the monitoring of artificial release. Intact genomic DNA was extracted from alcoholsoaked fins of the first filial generation of Chinese sucker released artificially in Wuhan City, Hubei Province and Yibin City, Sichuan Province, and a microsatellite enrichment library of Chinese sucker was constructed by FIASCO (fast isolation by AFLP of sequences containing repeats) magnetic bead enrichment method using synthesized biotinlabeled (AAAG)7 probe. Eighteen pairs of Chinese sucker microsatellite primers were designed and synthesized. After the validity test, they can be applied to further study on the genetic diversity and population genetic structure of Chinese sucker and the evaluation of enhancement effect. Yang et al.［36］ used microsatellite molecular markers to analyze the genetic diversity and population genetic structure of 80 individuals of the first filial generation of Chinese sucker artificially released in the middle and upper reaches of the Yangtze River. The results showed that 5 pairs of primers showed polymorphism, and the number of alleles was 2-8; the polymorphic information content was 0.295 7-0.803 8; the Shannon diversity index was 0.546 6-1.884 0; the observed heterozygosity was 0.305 6-0.722 2; the expected heterozygosity was 0.365 8-0.838 1; and the HardWeinberg genetic deviation Index (D) was 0.181 8-0. 428 7. The results reflected that the first filial generation of the artificiallyreleased Chinese sucker had higher polymorphic level and abundant genetic diversity, but its population structure and germplasm resources were seriously interfered by human factors, resulting in a decrease in the maintenance ability of population genetic diversity. The fragmentation and blocking of habitats formed by the construction of largescale water conservancy projects such as the Three Gorges Dam and Gezhouba cause genetic exchange and genetic differentiation between the upstream and downstream Chinese sucker populations, and combined with interference factors including change of hydrological conditions, overfishing and water pollution, the population structure and sex ratio are also severely affected.

Proliferation by releasing is an effective way to restore the wild population resources of Chinese sucker. Cheng et al.［37］ used 11 pairs of published Chinese sucker polymorphic microsatellite markers to evaluate the enhancement effect of Chinese sucker in the middle and upper reaches of the Yangtze River. Among the 65 samples collected, 11 samples were determined to have parentchild relationship with the breeding parents in the farm, and the contribution of the released Chinese sucker to the wild population in the middle and upper reaches of the Yangtze River was 16.92%. Hu et al.［38］ used 13 microsatellite markers to study the genetic diversity and genetic structure of the first filial generation populations of three Chinese sucker breeding bases (Chongqing, and Yongfeng and Xingan of Jiangxi Province). There was genetic differentiation among the three cultured populations, among which there was significant genetic differentiation in the cultured Chinese sucker population from Xingan of Jiangxi Province, and the genetic structure analysis of the five Chinese sucker individuals collected from the Ganjiang River showed that they might be from the first filial generation populations of Yongfeng and Xingan Chinese sucker breeding bases.

Comparison of nutritional components

In the nature, Chinese sucker prefers to eat benthic organisms such as oligochaete worms and water earthworms. In the case of artificial breeding, feed is mainly used. Due to differences in growth environments and baits, differences might be caused in muscle nutritional components between the wild population and the cultured population of Chinese sucker. Lin et al.［39］ compared the muscle nutritional components in wildcaught and artificiallycultured Chinese sucker, which had a body weight of (447.5±20.5) g and (484.3±19.6) g, respectively, and found that wildcaught Chinese sucker had water, crude ash and crude protein contents in muscles significantly higher than cultured Chinese sucker, while its meat content and crude fat content were significantly lower than cultured Chinese sucker. Therefore, the differences in nutritional components between wildcaught and cultured Chinese suckers can also be used as a supplement means to the monitoring and evaluation of Chinese sucker resources.

Jiansheng YE et al. Study on Resource Conservation of Chinese Sucker (Myxocyprinus asiaticus)

Research Prospect

As Chinas fishery administration, water conservancy and other relevant authorities pay more and more attention to the resource conservation of Chinese sucker, although many research institutes and colleges have done a lot of research work on resource conservation of Chinese sucker, it is unlikely that the resources can naturally proliferate and restore in a short period of time depending on wild environment because Chinese sucker has the characteristics of late sexual maturation, low reproductive rate, long development time and low survival rate. Therefore, it is necessary to strengthen following aspects in the resource protection of Chinese sucker:

(i) Increasing intensity of artificial release should be continued. Artificial release is the most effective way to protect and restore Chinese sucker resources in the Yangtze River. At present, there has been great progress in artificial breeding and larval rearing techniques of Chinese sucker, Chinese sucker fingerlings have been produced in large scale, and the fingerlings can ingested commercial feed under domestication conditions. It is recommended to strengthen the artificial release of Chinese sucker, to release Chinese sucker fry in the upper and lower reaches of the Yangtze River in the area suitable for the growth of Chinese sucker, and to release some largesized (500 g of oneyearold fish) individuals in the most suitable area for Chinese sucker, so as to increase survival rate and enhancement effect, and tagging release could be performed for the assessment and monitoring of the enhancement effect of artificial release.

(ii) Strengthening environmental protection should be continued. The provinces, counties, cities and counties of the upper, middle and lower reaches of the Yangtze River have established very wellestablished institutions for fishery management and resource protection, and the phenomenon that industrial and agricultural wastes and construction wastes arbitrarily discharged along the Yangtze River seriously destroy Chinese sucker resources and pollute water environment, has been basically curbed. With the promulgation and implementation of various national environmental protection policies and regulations, it is necessary to increase the awareness of environmental protection, and fundamentally improve the pollution along the river waters as soon as possible, which will have a positive and beneficial impact on the resource protection and restoration of Chinese sucker.

(iii) In addition, Chinese sucker nature reserves should be established in suitable waters with good water quality and abundant aquatic plant and animal resources, and the national fishery ban policy should be strictly enforced in the nature reserves. At the same time, in the process of protecting Chinese sucker resources, there are still many problems that need to be systematically studied and solved, such as how to improve the enhancement effect of artificial release on Chinese sucker, how to improve the survival rate of artificiallybred fingerlings in wild environments and how to promote natural reproduction of released Chinese sucker.

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