海洋生态与环境科学重点实验室知识库

血卵涡鞭虫（Hematodinium）是一类危害海水甲壳动物的寄生甲藻，在全球范围内多种经济甲壳动物中造成流行性病害，给渔业生产造成重大经济损失。血卵涡鞭虫流行病频繁在我国沿海地区爆发，已经成为危害我国海水甲壳类养殖业可持续发展的新兴致病性病原。目前，对于血卵涡鞭虫的研究主要集中在物种鉴定、检测技术、病原互作机制、生活史及其流行病学特征等方面，缺乏对于其传播途径和流行病发生模式的系统研究。血卵涡鞭虫流行病发生过程的相关研究主要集中于经济甲壳动物的野生群体，而我国沿海经济甲壳动物养殖普遍采用池塘内混合养殖模式，对于血卵涡鞭虫如何在其中传播，进而引发流行病的生态学过程，以及与流行病发生相关的生物、环境驱动因子无相关研究。因此，本论文从血卵涡鞭虫的荟萃分析入手，梳理血卵涡鞭虫宿主的种类和分布，归纳宿主的分类地位结构特征，解析血卵涡鞭虫流行病的发生模式，筛选影响流行病发生的关键因子；在我国近海典型三疣梭子蟹养殖区开展系统调查，揭示该区域血卵涡鞭虫宿主多样性，确定易感宿主种类和感染特征，辩析三疣梭子蟹养殖区与血卵涡鞭虫流行病发生过程相关的关键环境因子和主要生物因子；通过实验室控制实验及养殖池内模拟实验，明确血卵涡鞭虫的传播途径并验证其在养殖池内传播的有效性。主要研究发现如下：

1. 基于荟萃分析，发现血卵涡鞭虫在全球分布广泛，主要分布在北半球；目前，已报道发现70余种血卵涡鞭虫的宿主，分属于2目、34科、49属。在美国、欧洲以及我国沿海等不同区域，血卵涡鞭虫流行病发生模式之间存在差异；在不同宿主中，血卵涡鞭虫流行病发生模式存在差异，其中温度和盐度是影响血卵涡鞭虫流行病发生的关键环境因子。

2. 流行于我国山东沿海三疣梭子蟹养殖区的血卵涡鞭虫属于Hematodinium perezi genotype II型，在养殖区发现5种野生甲壳宿主，包括天津厚蟹（Helice tientsinensis）、伍氏拟厚蟹（Helice wuana）、弧边管招潮蟹（Uca arcuate）等。天津厚蟹中存在较高的感染率（30.1 %）和易感性（75 %），是当地血卵涡鞭虫的主要野生宿主。天津厚蟹中存在血卵涡鞭虫的持续感染（4-10月），是当地血卵涡鞭虫的重要越冬或保虫宿主，在流行病的发生中起着重要作用。

3. 三疣梭子蟹养殖池内的“哨兵”实验证明了水体传播是血卵涡鞭虫在养殖群体中有效的传播途径（感染率60.8-63.6 %）。室内水体传播控制实验进一步证明了经由孢子的水体传播是血卵涡鞭虫的有效传播途径，其中共栖实验中的感染率为15.4-40.7 %，暴露实验中的感染率为57.9-60.5 %，而同类残食不是有效的传播途径。天津厚蟹中的血卵涡鞭虫可经水体传播感染三疣梭子蟹，养殖区域天津厚蟹中的血卵涡鞭虫感染早于且持续存在于整个三疣梭子蟹养殖季，是病原的重要来源。

4. 天津厚蟹和弧边管招潮蟹等野生宿主的感染率与三疣梭子蟹的感染率呈显著正相关，宿主多样性与养殖区血卵涡鞭虫流行病发生密切相关。温度和盐度是影响血卵涡鞭虫流行病发生的关键环境因子，流行病的发生与温度呈正相关，而与盐度呈负相关。养殖区环境水体中存在多种与血卵涡鞭虫显著相关的真核微生物，包括拟裸口虫属（Pseudoholophrya）、硅鞭藻属（Dictyocha）等，真核微生物可能对宿主易感性变化、血卵涡鞭虫生活史转化等流行病发生的关键环节有着潜在的影响。

本研究首次完成了对已发表血卵涡鞭虫文献和数据的荟萃分析，对血卵涡鞭虫的分布以及宿主多样性进行了全面的总结，解析了血卵涡鞭虫流行病发生模式并筛选出影响流行病发生的关键因子。基于对我国近海典型三疣梭子蟹养殖区的系统研究，明确了当地血卵涡鞭虫传播途径以及关键环境因子和主要生物因子，提出了当地血卵涡鞭虫流行病的发生模式。本研究将有助于丰富和完善对海洋寄生甲藻血卵涡鞭虫的科学认知，弥补在血卵涡鞭虫传播途径及流行病发生模式等研究方面的不足，为预防和控制血卵涡鞭虫流行病提供理论依据。

Hematodinium was a type of parasitic dinoflagellate infecting marine crustaceans, resulting in significant economic loss to the fishery of several commercially valuable marine crustacea around the world. Hematodinium epizootics had expanded along China coast and became an emerging infectious pathogen impacting the sustainable development of mariculture. The current studies of Hematodinium were focused on hosts identification, parasite detection, host-parasite interactions, parasite life cycles and epizoology, while there were few synthetic studies on epizootic processes and transmission patterns. Most research on Hematodinium epizootic processes were concentrated on wild crustaceans. Polyculture pond was general culture mode for crustacean industries along China coast. However, there were few studies on Hematodinium transmission pathway and epizootic pattern, as well as the biological and environmental driving factors related to the epizootics. Thus, this dissertation started with meta-analyses for inducing Hematodinium hosts species, distributions and taxonomy, revealing epizootics patterns and its key driving factors. Based on systematic surveys and experiments in the typical Portunus trituberculatus aquaculture area, this dissertation was trying to find Hematodinium hosts diversity and infection characteristics along China coast, to confirm the transmission pathway, to reveal the key driving factors as well as outbreak mechanism of Hematodinium epizootics. The major findings were listed as following:

1. Based on meta-analyses, Hematodinium had wide distribution around the world and its records were concentrated in the northern hemisphere. There were more than 70 different species of Hematodinium hosts, belonging to 2 orders, 34 families and 49 genera. Hematodinium epizootic patterns had spatial heterogeneity in different regions. The epizootic patterns in different hosts showed different characteristics, and temperature and salinity were the key driving factors.

2. The Hematodinium isolated from P. trituberculatus aquaculture area in Shandong province belonged to genotype II of Hematodinium perezi. In the local area, there were five wild crustacean hosts, including Helice tientsinensis, H. wuana and Uca arcuate, etc. The mudflat crab H. tientsinensis has a higher prevalence (30.1 %) and susceptibility (75 %), indicating it was the dominant wild host of Hematodinium in the local area. The mudflat crab H. tientsinensis had instant Hematodinium infection (April-Octorber), suggesting it may be the overwintering and reservoir host and played important role in the local Hematodinium epizootics.

3. The sentinel experiments in the P. trituberculatus polyculture ponds certificated that waterborne transmission was the effective pathway for Hematodinium in the cultured population (with prevalence 60.8-63.6 %). The cohabitation and exposure experiments indicated that waterborne transmission via dinospores was effective with prevalence 15.4-40.7 % and 57.9-60.5 %, respectively. While cannibalism was not the effective pathway. Hematodinium was transmittable from H. tientsinensis to P. trituberculatus and had the early infection in H. tientsinensis indicated that H. tientsinensis might be the source of Hematodinium during the intensive culture of P. trituberculatus.

4. Hematodinium prevalence in H. tientsinensis and U. arcuate had significantly positive correlation with P. trituberculatus, suggesting host biodiversity played important role in the epizootic in the local area. Water temperature and salinity were the key driving factors. The temperature had the positive correlation with epizootic processes, while salinity had the negative correlation. There were several genera had significant correlation with Hematodinium, including Pseudoholophrya, Dictyocha, etc., and might have potential influence on important epizootic processes such as host susceptibility, development of Hematodinium life cycles.

This dissertation carried out the first meta-analyses of Hematodnium hosts diversity and distribution and finished the systematic analyses of Hematodinium epizootic patterns as well as its driving factors. Based on the systematic field investigation and experiments in P. trituberculatus farms, this dissertation confirmed the transmission pathway of Hematodinium, and summarized its epizootic pattern in the local area. The major finding will contribute to a better understanding transmission pathway and epizootic pattern of Hematodinium and provide theoretical bases for the prevention of epizootics in aquaculture of the economic crustaceans.