四种营养物质添加对菲律宾蛤仔稚贝生长和体成分的影响
doi: 10.19663/j.issn2095-9869.20241121001
周羽佳1,2,3 , 薛素燕2,3 , 田阔1 , 庄浩楠2,3 , 焦明蕙2,3 , 邱彦国4 , 李昂2,3 , 李加琦2,3 , 毛玉泽1,2,3
1. 浙江海洋大学水产学院 浙江 舟山 316000
2. 海水养殖生物育种与可持续产出全国重点实验室 (中国水产科学研究院黄海水产研究所) 山东 青岛 266071
3. 青岛海洋科技中心海洋生态环境科学功能实验室 山东 青岛 266071
4. 山东得和明兴生物科技有限公司 山东 昌邑 261300
基金项目: 国家重点研发计划(2023YFD2400800)、中国水产科学研究院基本科研业务费(2023TD54)、中国水产科学研究院黄海水产研究所基本科研业务费(20603022023007)和山东省科技型中小企业创新能力提升工程项目(2023TSGC0768)共同资助
The Effects of Different Nutrient Supplements on the Growth and Body Composition of Juvenile Manila clams Ruditapes philippinarum
ZHOU Yujia1,2,3 , XUE Suyan2,3 , TIAN Kuo1 , ZHUANG Haonan2,3 , JIAO Minghui2,3 , QIU Yanguo4 , LI Ang2,3 , LI Jiaqi2,3 , MAO Yuze1,2,3
1. Fisheries College, Zhejiang Ocean University, Zhoushan 316000 , China
2. State Key Laboratory of Mariculture Biobreeding and Sustainable Goods, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071 , China
3. Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao 266071 , China
4. Dehe Mingxing Biotechnology Co., Ltd., Changyi 261300 , China
摘要
滩涂贝类稚贝的营养物质积累是影响其浅海增养殖成活率的关键因素。本研究采用实验生理生态学方法,探究了添加大豆肽、血浆蛋白粉、酵母和螺旋藻粉等 4 种营养物质对菲律宾蛤仔 (Ruditapes philippinarum)稚贝生长、存活和糖原、碳氮含量等体成分的影响。实验设置了有沙、无沙 2 种底质环境组和 4 种营养物质添加组(H1,大豆肽;H2,血浆蛋白粉;H3,酵母;H4,螺旋藻粉),不添加营养物质组作为对照(仅投喂微藻)。研究结果显示,H3 有底质组稚贝存活率最高 [(79.60±0.86)%],与无底质组相比差异显著(P<0.05);H4 底质组第 10 天时壳长特定生长率最大,为(1.09±0.09)%/d,H3 组第 10 天有底质时湿重特定生长率最大,为(3.11±0.62)%/d,底质有无对生长率的影响显著(P<0.05)。H4 有底质组稚贝糖原含量[(79.03±18.60) mg/g]显著高于其他各组 (P<0.05),有底质组和无底质组之间的糖原含量差异显著(P<0.05);在碳含量方面,H3 底质组稚贝的碳含量[(45.23±0.33)%]显著高于其他各组(P<0.05),H4 底质组稚贝的氮含量[(12.25±0.22)%]显著高于其他各组(P<0.05),而有底质和无底质组碳含量差异不显著(P>0.05),氮含量差异显著(P<0.05)。研究结果表明,营养物质的添加能够显著影响稚贝的生长率、存活率以及体内糖原积累和碳、氮含量,且与是否存在底质有一定关系,研究结果为菲律宾蛤仔健康苗种培育提供了参考。
Abstract

Shellfish inhabiting mudflats constitute an important component of the mariculture industry in China, with an annual output accounting for approximately one-third of shellfish breeding output. The Manila clam Ruditapes philippinarum, one of the main species of mudflat mollusks cultivated in China, is characterized by a short cultivation cycle and strong adaptability, the culture of which requires low investment and is highly profitable. Moreover, it is a suitable species for artificial high-density cultivation, with an annual output exceeding 3 million tons, accounting for more than 90% of the world's cultured production. R. philippinarum is one of the four major mollusk species traditionally cultured in China that is highly valued for its delicate taste and rich nutrition, and is particularly popular among the general public. The current domestic Manila clam aquaculture industry is based on a mainstream pattern of southern (Fujian Province) breeding and northern (Liaoning and Shandong Province) rearing of seedlings. During the entire Manila clam cultivation process, the intermediate stage of cultivation (cultivating juveniles to suitable sizes for bottom-seeding cultivation) is an important link connecting the two stages of factory-based seed production and bottom seedling cultivation. With the annually increasing market demand for Manila clams, the scale of cultivation scale has also expanded, making the intermediate cultivation stage particularly important. Currently, the southern intermediary stage of Manila clam juvenile cultivation is mainly carried out in natural marine areas, whereas the intermediate cultivation of northern Manila clam is mainly conducted in ponds. Although pond cultivation is conducive to artificial control and management, with juveniles being less affected by predators and more efficiently harvested, in northern regions this type of cultivation has the disadvantages of low temperatures in winter and insufficient food supplies. Consequently, the intermediate cultivation of juvenile shellfish is typically one of the key factors currently constraining the further development of the industry. Studies in this regard have shown that the accumulation of nutrients in juvenile shellfish plays a decisive role in the survival of juveniles for enhanced breeding success, and this requirement is accordingly gaining increasing attention from breeding enterprises and researchers, given that ensuring a sufficient food supply during the intermediate stage of juvenile cultivation is a key factor contributing to the success of the entire cultivation process.

In this study, to address the problems of feed shortages or nutritional deficiencies during Manila clam cultivation, we sought to identify effective or alternative feed supplements by assessing the effects of the addition of four nutritionally rich and readily obtainable feed sources, namely, spirulina powder, yeast, plasma protein powder, and soybean peptides. Soybean peptides represent a high-protein source that is obtained by harnessing biological enzymatic technology to degrade large soybean protein molecules to smaller molecular fragments. This process yields a rich array of amino acids, thereby making soybean peptides not only a concentrated source of protein but also a potentially beneficial component for enhancing the growth and immune function of mollusks in aquaculture. Plasma is the liquid fraction of blood that contains a diverse range of proteins, minerals, hormones, and spectrum of essential nutrients. For the purposes of aquaculture, it can be converted to a plasma protein powder and used as a protein supplement, providing a source of essential nutrients for mollusks. Yeast is a nutrient-rich source of microbial proteins, B-vitamins, minerals, and dietary fiber, which can be used as a nutritional supplement that may contribute to enhancing the nutritional value and growth performance of young Manila clams. Spirulina is a high-quality plant-based source of nutrients that is rich in proteins, vitamins, minerals, and essential amino acids, which may have a significant influence on the fat content of Manila clams and also contributes to enhancing immunity.

To investigate the effects of soybean peptide, plasma protein powder, and yeast and spirulina powder on the growth, survival, and nutrient accumulation of R. philippinarum juveniles, in this study, we adopted a physiological ecology approach. Specifically, we compared two substrate conditions (with and without sand) for each of the following four supplemental nutrient groups: H1 (soybean peptide), H2 (plasma protein powder), H3 (yeast), and H4 (spirulina powder). As a control group, shellfish were fed solely on microalgae, without nutrient supplementation. The results revealed that among the assessed feed supplements, the survival of juveniles cultivated on a sandy substrate and receiving yeast supplementation was notably higher at (79.60±0.86)%, which was significantly higher than that of juveniles reared in the absence of a sandy substrate (P<0.05). On the tenth day of observations, a maximum shell length specific growth rate of (1.09±0.09)%/d was recorded in the H4 group cultivated with sand, whereas a maximum wet weight specific growth rate of (3.11±0.62)%/d was recorded for H3 group clams cultivated with sand. And the effect of substratum on growth rate was found to be significant (P<0.05). Furthermore, the glycogen content of H4 group R. philippinarum juveniles cultivated with sand (79.03±18.60 mg/g) was significantly higher than that in all other groups (P<0.05), with this difference between the groups with and without sand also being statistically significant (P<0.05). The carbon content of juveniles in the H3 group with sand (45.23%±0.33%) was significantly higher than that observed in the other groups (P<0.05), whereas the nitrogen content of juveniles in the H4 group with sand (12.25%±0.22%) was significantly elevated compared with that detected in the other groups (P<0.05). However, whereas with respect to carbon content, we detected no significant differences between the groups cultivated with and without a sand substratum (P>0.05), the presence of a substratum did have a significant effect on nitrogen content (P<0.05).

In conclusion, our findings in this study provide evidence to indicate that nutrient supplementation can contribute to a significant alteration in the nutrient content of R. philippinarum juveniles, and that these effects are partially influenced by the presence of sand. The valuable insights gained in this study will contribute to developing systems for the efficient cultivation of healthy R. philippinarum juveniles.

滩涂贝类是我国贝类养殖的重要类群,年产量约占贝类养殖产量的 1/3(农业农村部渔业渔政管理局等,2023),菲律宾蛤仔(Ruditapes philippinarum)是我国滩涂贝类养殖的主要品种之一,年产量超过 300 万 t(任恺佳等,2024),占世界养殖产量的 90%以上,其肉嫩味美、营养丰富,广受大众喜爱。菲律宾蛤苗种主要来源于福建和广西等地,但近期出现苗种良莠不齐的现象,制约了产业的发展,而稚贝中间培育也是制约产业发展的关键因素之一(闫喜武等,2006)。研究表明,稚贝的营养物质积累对贝类增养殖的成活率具有决定性作用,得到越来越多养殖企业和研究者的重视(杨守国,2022)。
确保中间培育阶段饵料营养供应对菲律宾蛤仔稚贝养殖过程至关重要。饵料是影响双壳贝类生长的主要因素,饲喂不同饵料会产生不同的生长速率(Jung et al,2016)。菲律宾蛤仔苗种繁育和中间培育过程中受饵料影响很大,饵料的数量和质量均会影响其生长发育(何苗等,2017),投喂单一饵料往往会由于某些营养成份不足而影响稚贝的生长速度(何进金等,1984)。为了解决工厂化养殖过程中单胞藻饵料的不足,国内外研究者已开展了代用饵料或人工配合饲料的研究(敬庭森等,2021; 杨创业等,2016),但这些饵料在工厂化养殖中的效果尚未开展系统评估,且这些饵料对于贝类体成分影响的研究也较少。糖原是一种水溶性多糖,是生物体内重要的能量储备物质(陈燕园,2020),也是动物碳水化合物贮存的主要形式,常被用来评估贝类水产品口感品质,其含量变化是衡量动物性食品品质的重要指标(梅丽敏等,2023)。碳元素是构成糖类等碳源物质碳架的主要成分,氮元素主要以蛋白质的形式存在于海水贝类体内(潘兆基等,2023)。因此,评估营养物质对贝类体成分的影响对其健康状态、生物活性和营养价值等都具有重要意义。
大豆肽作为一种高蛋白源,是由大分子的大豆蛋白质经过生物酶解技术提炼成的小分子片段(Singh et al,2014),具有良好的溶解性和易消化吸收的特性,对贝类的生长、免疫有积极作用;血浆蛋白粉(晋鹏飞,2018)在水产养殖领域中可用作蛋白质补充,血浆蛋白粉是利用屠宰后动物的血液制成的,这些血液往往被视作废弃物丢弃,导致蛋白质资源的流失,通过将其制成血浆蛋白粉可以减少资源浪费和环境污染;酵母(Aslankoohi et al,2016)具有较高的生物价值,有助于改善菲律宾蛤仔稚贝的生长和存活,可以从啤酒工业的废弃物中提取,能够促进资源循环利用;螺旋藻是一种优质的植物性蛋白源,具有一定的固碳价值,对菲律宾蛤仔的肥满度、免疫力增强等有显著影响。本研究通过添加营养价值较高、易于获取的大豆肽(Tan et al,2023)、酵母(Nell et al,1996)、鸡血血浆蛋白粉(杨恒等,2019)以及螺旋藻粉(Batista et al,2013)等营养物质作为菲律宾蛤仔稚贝的饵料营养补充,旨在探讨不同营养物质添加对菲律宾蛤仔稚贝生长、存活和营养物质积累的影响,为培养滩涂贝类健康苗种提供理论依据。
1 材料与方法
1.1 实验材料
本实验用的菲律宾蛤仔稚贝来自山东得和明兴生物科技有限公司。实验前将稚贝在实验室循环水养殖系统中暂养 7 d,早、中、晚各投喂一次微藻饵料(角毛藻 Chaetoceros spp.和小球藻 Chlorella vulgaris),按天为单位交替投喂,二者比例大致为 1∶1,投喂后水体藻浓度达到 1×105 cells/mL。实验期间水温为(20±2)℃,海水盐度为 28±1,pH 值为 8.0±0.2,溶解氧为(7.0±0.5)mg/L。
1.2 实验设计
实验在中国水产研究院黄海水产研究所琅琊基地进行,选取活力强、无损伤的健康个体[(壳长 10.14± 2.01)mm]进行实验。稚贝养殖在循环水系统的玻璃缸(20 cm×40 cm×40 cm)中,考虑设施化中间培育需求,实验设置有底质和无底质组,分别添加 4 种不同的营养物质,不添加营养物质的为对照组,共 10 个处理组(表1),每个处理组 3 个重复,每个重复放置 250 个稚贝( 约 48.75 g)。实验期间,投喂微藻密度为 1×105 cells/mL,营养物质添加量为稚贝湿重的 3%(1.46 g),将营养物质用海水浸泡混匀,用 400 目筛网过滤后每天早、中、晚各投喂一次饵料,根据残饵和稚贝体湿重变化,适时调整日投饵量。实验时间为 60 d。
1.3 生长率和存活率测定
实验前,随机取 50 只蛤仔稚贝,用吸水纸吸干稚贝体表的水分,使用游标卡尺测量稚贝的壳长、壳高和壳宽(精度为 0.01 mm),用电子天平称量稚贝的体湿重(精度为 0.01 g)。每隔 10 d 从每个处理组随机取 30 个稚贝,测定壳长、壳宽、壳高和体湿重,计算壳长和湿重特定生长率(SGR),实验结束时计算稚贝的存活率。
SGR(%/d)=100×lnX2-X1t2-t1
(1)
式中,t1t2 分别为实验的起始时间和结束时间,X1X2 分别为实验的起始测量值(壳长、体湿重)和结束测量值。
存活率 (%)= 终末稚贝数量/初始稚贝数量 ×100%
(2)
实验结束后,每个处理组分别取 20 只稚贝活体解剖,为减少个体误差,将软组织取出后混合,其中一部分软组织冻干研磨,采用微量蒽酮法测定糖原含量; 另一部分软组织烘干、研磨备用,测其碳含量与氮含量。
1不同处理营养物质添加情况
Tab.1Nutrient supplementation in different treatments
注:单胞藻种类包括扁藻(Tetraselmis subcordiformis)、金藻(Isochrysis galbana)、小球藻和硅藻(Phaeodactylum tricornutum)。YC:有底质时对照组;YH:有底质时不同处理组;NC:无底质时对照组;NH:无底质时不同处理组。
Note: Unicellular algae include Tetraselmis subcordiformis, Isochrysis galbana, Chlorella vulgaris and Phaeodactylum tricornutum. YC: Control group with substrate; YH: Treatment groups with substrate; NC: Control group without substrate; NH: Treatment groups without substrate.
1.4 数据处理与分析
对数据进行正态性检验和方差齐性检验,采用单因素方差分析(one-way ANOVA)检验各组间差异性,采用双因素方差分析(two-way ANOVA)检验主效应及其交互效应,采用 Turkey HSD 法进行组间的差异性比较,以 P<0.05 作为不同处理组间差异显著标准。以上数据处理均使用软件 R 3.6.2 完成,使用 Origin2021 软件进行图形的绘制。
2 结果
2.1 存活与生长
2.1.1 菲律宾蛤仔稚贝的存活率
不同处理组菲律宾蛤仔稚贝的存活率如图1所示,经单因素方差分析,有底质组蛤仔稚贝存活率高于无底质组,除 YH2 组显著高于 NH2 组外,其余各处理组有无底质差异均不显著(P>0.05)。其中,YH3 组稚贝存活率最高(79.60±0.86)%,NH1 组稚贝存活率最低(46.67±3.30)%。
2.1.2 特定生长率
(1)壳长特定生长率
不同处理组菲律宾蛤仔稚贝的壳长特定生长率如图2所示,经双因素方差分析,有无底质和不同营养物质的主效应和交互作用对稚贝壳长特定生长率均影响显著(P<0.05),多重比较分析,NH3 组和 YH3 组稚贝壳长特定生长率差异显著(P<0.05)。无底质组中,实验开始 10 d 时,NH1 和 NH2 组稚贝的壳长特定生长率均显著高于对照组(P<0.05),分别为(0.97±0.14)%/d 和(0.96±0.09)%/d。实验开始后第 20 天时,NH2 组稚贝的壳长特定生长率显著高于对照组(P<0.05),为(0.86±0.24)%/d。实验开始后第 60 天时, NH3 组稚贝的壳长特定生长率最低,为(0.24± 0.03)%/d。有底质组中,实验开始后第 10 天时,YH3 组和 YH4 组稚贝壳长特定生长率显著高于对照组,分别为(1.08±0.25)%/d 和(1.09±0.09)%/d。
1不同处理组菲律宾蛤仔稚贝的存活率
Fig.1Survival rate of R. philippinarum juveniles in different treatment groups
NC:无底质对照组;NH1:无底质,投喂微藻和大豆肽; NH2:无底质,投喂微藻和血浆蛋白粉;NH3:无底质,投喂微藻和酵母;NH4:无底质,投喂微藻和螺旋藻粉; YC:有底质对照组;YH1:有底质,投喂微藻和大豆肽; YH2:有底质,投喂微藻和血浆蛋白粉;YH3:有底质,投喂微藻和血浆;YH4:有底质,投喂微藻和螺旋藻粉。不同字母表示组间差异显著(P<0.05)。下同。
NC: No substrate and with algae; NH1: No substrate, with algae and soybean peptide; NH2: No substrate, with algae and plasma protein powder; NH3: No substrate, with algae and yeast; NH4: No substrate, with algae and spirulina powder; YC: With substrate and with algae; YH1: With substrate, with algae and sybean peptide; YH2: With substrate, with algae and plasma protein powder; YH3: With substrate, with algae and yeast; YH4: With substrate, with algae and spirulina powder. Different letters indicate significant differences between groups (P<0.05) . The same below.
(2)湿重特定生长率
不同处理组菲律宾蛤仔稚贝的湿重特定生长率如图3所示,经双因素方差分析,有无底质和不同营养物质的主效应和交互作用对稚贝湿重特定生长率均影响显著(P<0.05)。多重比较分析发现,无底质时 NH3 组稚贝湿重特定生长率与 NC 组差异显著(P<0.05)。无底质组中,NC 组稚贝的湿重特定生长率在养殖 10 d 时最大,为(2.40±0.49)%/d,NH3 组稚贝的湿重特定生长率在养殖 60 d 时最小,为(0.60± 0.09)%/d。有底质组中,YH1 在实验开始第 10 天和第 40 天均显著低于对照组(P<0.05)。YH3 组蛤仔稚贝的湿重特定生长率在养殖 10 d 时最大,为(3.11± 0.62)%/d,YH1 组蛤仔稚贝的湿重特定生长率在养殖 60 d 时最小,为(0.65±0.12)%/d。
2.2 体成分
2.2.1 糖原含量
不同处理组菲律宾蛤仔稚贝软组织的糖原含量如图4所示,经双因素方差分析,有无底质和不同营养物质的主效应和交互作用对稚贝软组织糖原含量均影响显著(P<0.05)。多重比较可知,有底质组中 YH4 组糖原含量显著高于其他各组(P<0.05)。H4 组有无底质时稚贝糖原含量差异显著(P<0.05)。无底质组中,NC 组糖原含量显著高于其他各组(P<0.05),为(63.52±9.89)mg/g。NH2 组糖原含量最低,为(40.90±5.52)mg/g。有底质组中,YH4 糖原含量显著高于其他各组(P<0.05),为(79.03± 18.60)mg/g,YH2 糖原含量最低,为(51.19±14.42)mg/g。
2.2.2 碳、氮含量
不同处理组菲律宾蛤仔稚贝软组织的碳含量如图5所示,经双因素方差分析,有无底质和不同营养物质的交互作用对稚贝软组织碳含量影响不显著(P>0.05)。单因素方差分析显示,各处理组稚贝碳含量差异显著(P<0.05),有无底质差异不显著(P>0.05)。H3 和 H4 碳含量均显著高于对照组(P<0.05),H1 和 H2 稚贝碳含量除 YH2 组外均显著低于对照组(P<0.05)。无底质时,NH3 组稚贝软组织碳含量最高,为(45.23±0.49)%;NH1 组稚贝软组织碳含量最低,为(33.34±0.74)%。有底质组中,YH3 组稚贝软组织碳含量高,为(45.23±0.33)%;YH1 组稚贝软组织碳含量最低,为(32.44±0.01)%。
2不同处理组菲律宾蛤仔稚贝壳长特定生长率
Fig.2Specific growth rate of juveniles length of R. philippinarum in different treatment groups
a:无底质;b:有底质。*表示各处理组在不同天数组内差异显著(P<0.05),下同。
a: No substrate; b: With substrate. *indicate significant differences among groups within individual days (P<0.05) . The same below.
3不同处理组菲律宾蛤仔稚贝湿重特定生长率
Fig.3Specific growth rate of juveniles wet-weight of R. philippinarum in different treatment groups
a:无底质;b:有底质。
a: No substrate; b: With substrate.
4不同处理组菲律宾蛤仔稚贝糖原含量
Fig.4Glycogen content of R. philippinarum juveniles in different treatment groups
*表示不同处理组间差异显著(P<0.05),不同字母表示组内差异显著(P<0.05)。下同。
* indicate significant differences between groups, and different letters indicate significant differences between treatments. The same below.
5不同处理组菲律宾蛤仔稚贝软组织碳含量
Fig.5Soft tissue carbon content of R. philippinarum juveniles in different treatment groups
不同处理组菲律宾蛤仔稚贝软组织的氮含量如图6所示,经双因素方差分析,有无底质和不同营养物质的主效应和交互作用对稚贝软组织氮含量均影响显著(P<0.05),通过事后多重比较可知,无底质组中 NH3 和 NH4 组软组织氮含量显著高于其他各组(P<0.05),有底质组中 YH4 组软组织氮含量显著高于其他各组(P<0.05)。无底质组中,NH4 稚贝软组织氮含量最高,为(12.06±0.07)%;NH2 稚贝软组织氮含量最低,为(8.58±0.17)%。有底质时,YH4 稚贝软组织氮含量最高,为(12.25±0.22)%;YH1 稚贝软组织氮含量最低,为(7.51±0.20)%。
不同处理组菲律宾蛤仔稚贝软组织的 C/N 如图7所示,经双因素方差分析显示,有无底质和不同营养物质的交互作用对稚贝软组织 C/N 影响显著(P<0.05)。单因素方差分析可知,H2 组有无底质时稚贝软组织 C/N 差异显著。无底质组中,各处理组蛤仔稚贝软组织 C/N 均高于对照组,但差异不显著(P>0.05)。NH1 组蛤仔稚贝软组织 C/N 最高,为 3.92±0.01,NC 组蛤仔稚贝软组织 C/N 最低,为 3.83±0.04。YH1 和 YH2 均低于 YC,YH3 和 YH4 高于 YC,但无显著性差异(P>0.05)。有底质组中,YH4 组蛤仔稚贝软组织 C/N最高,为 3.85±0.06,YH2 组蛤仔稚贝软组织 C/N 最低,为 3.68±0.04。
6不同处理组菲律宾蛤仔稚贝软组织氮含量
Fig.6Soft tissue nitrogen content of R. philippinarum juveniles in different treatment groups
7不同处理组菲律宾蛤仔稚贝软组织 C/N
Fig.7Soft tissue C/N of R. philippinarum juveniles in different treatment groups
表2所示,4 种营养物质的碳含量有显著差异(P<0.05),其中,酵母碳含量最高,为(38.63±0.26)%,血浆蛋白粉碳含量最低,为(14.80±0.40)%。4 种营养物质所含氮含量有显著差异(P<0.05),其中,酵母氮含量最低,为(6.07±0.04)%,血浆蛋白粉氮含量最高,为(9.97±0.09)%。同样,C/N 也具有显著差异(P<0.05),其中,血浆蛋白粉 C/N 最低,为 1.49±0.05,酵母 C/N 最高,为 6.37±0.09。
24 种营养物质碳氮含量及 C/N(平均值±标准误)
Tab.2Carbon content, nitrogen content and C/N of four substitute diets (Mean±SE)
注:不同字母表示不同营养物质碳氮含量及 C/N 差异显著(P<0.05)。
Notes: Different letters represent different nutrients with significant differences in carbon content, nitrogen content and C/N (P<0.05) .
3 讨论
3.1 不同营养物质添加对菲律宾蛤仔稚贝生长和存活的影响
有学者认为菲律宾蛤仔倾向于摄食 3~20 μm 大小的食物颗粒(Defossez et al,1997),且对于高有机物含量的食物颗粒有更高的选择性(董波等,2000)。螺旋藻粉和酵母作为贝苗饵料,不但颗粒大小适口,而且营养成分丰富,尤其是蛋白质含量都较高,螺旋藻的蛋白质含量可达干重的 60%~72%。酵母蛋白质含量达 47%~56%(黄玲,1992)。已有实验证明,蛋白质含量与蛤蜊生长速率显著相关(Wikfors et al,1992)。此外,螺旋藻细胞壁纤维相比其他藻类少,所以壁内营养物质更易被机体吸收。这可能与实验初期 YH3 组、YH4 组壳长特定生长率较高有关。YH3 组特定生长率高于 NH3 组的原因可能是底质组稚贝除了可以滤食附着在微藻上的营养物质颗粒外,还可滤食沉积到底泥中的部分有机颗粒。有实验研究了虾片、黑粒、螺旋藻粉 3 种人工饵料单独投喂及与虾元和 B.P.(博尚牌 B.P.)饵料添加剂混合投喂 14 d 后对方斑东风螺(Babylonia areolata)幼虫生长及存活的影响(姚高友等,2018),结果表明,人工饵料与添加剂混合投喂时,幼虫的存活率、壳长及特定生长率高于均单一投喂实验组,与本实验结果相似。营养物质的添加一定程度补充了中间培育过程中菲律宾蛤仔稚贝所需的蛋白质等营养成分,促进其快速生长。
此外,营养物质也会对微藻的生长和色素含量产生一定的影响。有研究者基于转录组测序技术分别对蛋白核小球藻(Chlorella pyrenoidosa)和粘红酵母(Rhodotorula glutinis TISTR 5159)共培养前期的基因转录水平进行了全局性监测。结果显示,蛋白核小球藻响应共培养环境,可引起叶绿素代谢相关酶的调控基因显著上调,这表明酵母的存在可能通过影响微藻的基因表达来影响叶绿素 a 的含量(刘鹭,2019)。罗龙皂等(2019)探究了藻–菌初始接种比例和废水有机负荷对系统中微藻生长的影响,发现微藻生物量随菌–藻接种比例的增大而增加,当菌–藻接种比例为 100∶1 时,系统中微藻生物量最大,这表明在适宜的接种比例下,酵母的存在对微藻生长有积极的影响,从而间接促进贝类的生长。本实验中的不同营养物质对微藻生长和色素含量可能也存在一定影响,其详细机制有待后续深入探索。
3.2 不同营养物质添加对菲律宾蛤仔稚贝糖原及碳氮含量的影响
有研究发现,糖原对贝类的死亡率有一定的影响,在不利的环境中,糖原含量高的贝类抵御外界环境能力强,能够减少细胞损伤、降低死亡率(Ren et al,2003)。与上述结论相似,本研究中 YH4 稚贝的糖原含量较高,相应地,其死亡率也较低;NH1 和 NH2 稚贝的糖原含量较低,其死亡率则较高。另外,大豆肽中糖类含量低于 10%(吴昊怡等,2024),鸡血血浆蛋白粉中糖类和脂肪含量较少(杨恒等,2019),这可能是造成 NH1 和 NH2 组糖原含量较低的原因之一。酵母和螺旋藻粉中蛋白质含量较高,而蛋白质的代谢产物氨基酸可在脱氨基后生成相应的 α-酮酸,后转变为葡萄糖并结合为糖原,故 H3 和 H4 组稚贝糖原含量较高。
在本实验中,无底质时饵料的碳含量与菲律宾蛤仔软组织糖原含量成正相关,说明饵料中的碳可以被菲律宾蛤仔稚贝吸收并且用于合成自身组分,满足生长所需。菲律宾蛤仔稚贝软组织 C/N 较高的组,如 H2 组,其碳含量较低,这与饵料本身碳含量较低有关。稚贝在不同的生长阶段对碳氮的需求不同。例如,在快速生长期,稚贝可能需要更多的氮来合成蛋白质和其他含氮化合物。高质量的饵料(即有机物含量高的饵料)更容易被稚贝消化吸收,从而更有效地促进生长和碳氮的积累。
有研究表明,贻贝(Mytilus edulis)主要由高达 66% 的脂质、25%的蛋白质和 6%的碳水化合物组成(Ibarrola et al,2000)。营养供给会影响贝类摄食和消化平衡速率,这与贝类自身组成无关(Arranz et al,2022)。贝类对低碳氮比的微藻和高碳氮比的沉积有机颗粒有较高的选择性,进食后也会有类似的选择机制。对于氮含量较低的饵料,贝类会优先摄入蛋白氮来补偿其营养缺陷(Navarro et al,2016)。本研究中,酵母和螺旋藻粉氮含量较低,稚贝软组织中氮含量反而较高,这是由于在氮输入较少的情况下,蛋白质分解和合成的比例会增加,蛋白质合成的转氨化反应为氮库提供充足的燃料(Hawkins,1985),从而积累较多蛋白氮。有研究表明,喂食低氮饵料的贻贝比喂食高氮饵料的贻贝摄食率也有所增加(Bayne et al,2017)。本研究中,大豆肽和血浆蛋白粉含氮量较高,而 H1 和 H2 组稚贝软组织氮含量不高的原因是饵料中氮含量较高时,贝类会通过增加氮排泄的方式来维持自身质量平衡(Anderson et al,2005),因而排出部分蛋白氮。此外,H1 和 H2 组稚贝软组织营养物质含量和特定生长率均不高,可能是由于大豆肽和血浆蛋白粉中氨基酸种类不均衡。有研究表明,在军曹鱼(Rachycentron canadum)幼鱼的鱼粉中添加一定量的蛋白替代饲料,导致饲料产生了营养缺陷,幼鱼生长率下降(李聪等,2018)。H3 和 H4 组的稚贝软组织碳、氮含量高于其他各组,说明酵母和螺旋藻粉作为营养物质可以有效补充稚贝生长过程中所需的蛋白质和糖类等营养物质。
综上所述,螺旋藻粉和微藻混合投喂时,稚贝软组织氮含量最高,有底质时其糖原含量最高;酵母和微藻混合投喂时,稚贝软组织碳含量最高。螺旋藻粉和酵母均能作为营养物质与微藻混合投喂有效补充中间培育阶段菲律宾蛤仔稚贝的营养需求。
1不同处理组菲律宾蛤仔稚贝的存活率
Fig.1Survival rate of R. philippinarum juveniles in different treatment groups
2不同处理组菲律宾蛤仔稚贝壳长特定生长率
Fig.2Specific growth rate of juveniles length of R. philippinarum in different treatment groups
3不同处理组菲律宾蛤仔稚贝湿重特定生长率
Fig.3Specific growth rate of juveniles wet-weight of R. philippinarum in different treatment groups
4不同处理组菲律宾蛤仔稚贝糖原含量
Fig.4Glycogen content of R. philippinarum juveniles in different treatment groups
5不同处理组菲律宾蛤仔稚贝软组织碳含量
Fig.5Soft tissue carbon content of R. philippinarum juveniles in different treatment groups
6不同处理组菲律宾蛤仔稚贝软组织氮含量
Fig.6Soft tissue nitrogen content of R. philippinarum juveniles in different treatment groups
7不同处理组菲律宾蛤仔稚贝软组织 C/N
Fig.7Soft tissue C/N of R. philippinarum juveniles in different treatment groups
1不同处理营养物质添加情况
Tab.1Nutrient supplementation in different treatments
24 种营养物质碳氮含量及 C/N(平均值±标准误)
Tab.2Carbon content, nitrogen content and C/N of four substitute diets (Mean±SE)
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