菲律宾蛤仔斑马蛤2号与未选育群体生理能量学对比研究
doi: 10.3969/j.issn.2095-9869.20250325001
袁明军1,2 , 蒋增杰1,3 , 姜娓娓1 , 蔺凡1 , 李伟伟1 , 郝紫冰1,4 , 张义涛5
1. 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中国水产科学研究院碳汇渔业重点实验室 山东 青岛 266071
2. 中国农业科学院研究生院 北京 100081
3. 青岛海洋科技中心海洋渔业科学与食物产出过程功能实验室 山东 青岛 266237
4. 上海海洋大学水产与生命学院 上海 201306
5. 荣成楮岛水产有限公司 山东 荣成 264312
基金项目: 国家自然科学基金面上项目(42376151;32303035)、山东省重点研发计划竞争性创新平台(2024CXPT071-3)、中国水产科学研究院基本科研业务费(2023TD54)和现代农业产业技术体系专项资金(CARS-49)共同资助
A Comparative Study of Physiological Energetics Between Zebra Clam 2 Ruditapes philippinarum and Unselected Group
YUAN Mingjun1,2 , JIANG Zengjie1,3 , JIANG Weiwei1 , LIN Fan1 , LI Weiwei1 , HAO Zibing1,4 , ZHANG Yitao5
1. State Key Laboratory of Mariculture Biobreeding and Sustainable Goods, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Key Laboratory of Carbon Sink Fisheries, Chinese Academy of Fishery Sciences, Qingdao 266071 , China
2. Graduate School of the Chinese Academy of Agricultural Sciences, Beijing 100081 , China
3. Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao Marine Science and Technology Center, Qingdao 266237 , China
4. College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306 , China
5. Rongcheng Chudao Aquaculture Corporation, Rongcheng 264312 , China
摘要
为明确菲律宾蛤仔(Ruditapes philippinarum)斑马蛤 2 号与未选育群体在能量分配方面是否存在差异,解析新品种斑马蛤 2 号生长速度快的内在机理,于 2023 年 7 月,以大、中、小 3 种规格(壳长分别为 40~45 mm、35~40 mm、30~35 mm)斑马蛤 2 号和未选育群体为实验对象,基于现场流水系统测定了摄食和代谢生理关键参数,对比分析了能量分配方式的不同。结果显示:3 种规格斑马蛤 2 号的滤水率和同化效率均高于未选育群体,但差异不显著(P>0.05);中规格斑马蛤 2 号耗氧率显著高于未选育群体(P<0.05),而小规格斑马蛤 2 号耗氧率显著低于未选育群体(P<0.05);中、小规格斑马蛤 2 号排氨率均显著高于未选育群体(P<0.05);从能量摄入角度来看,大、中、小规格的斑马蛤 2 号摄食能较未选育群体均有一定程度的提升,分别提升了 45.22%、18.60%和 21.40%。从能量分配角度来看,大、中、小规格的斑马蛤2号吸收能较未选育群体分别提升了54.90%、18.60%、 29.67%;大、中、小3种规格斑马蛤2号生长余力较未选育群体分别提升了57.65%、17.34%和31.79%。显示斑马蛤 2 号依靠较高的摄食能和略高的同化效率导致在能量分配中有更多能量用于生长,从而维持了较快的生长速度。研究结果为深化认识斑马蛤 2 号的生理学特征、进而服务新品种的养殖容量评估提供了基础数据。
Abstract

China is home to the most productive marine shellfish aquaculture industry, and aquaculture production has increased rapidly in recent decades. In 2023, production stood at 16,460,600 tons, with an aquaculture area of 1,357.53 thousand hectares. Marine shellfish farming in China has made important contribution to increasing fishermen's income, improving water transparency, alleviating water eutrophication, and actively responding to climate change. However, on the whole, the marine shellfish aquaculture industry in China is still a labor-intensive and volume-driven industry, and the improvement of aquaculture output is highly dependent on the expansion of the aquaculture area. In the past two decades, marine shellfish aquaculture in China has increased by 28.11% in terms of cultivation area and maintained a 54.19% increase in aquaculture output. With increasingly fierce competition for marine space resources from various marine industries such as coastal tourism and marine transportation, mariculture is increasingly constrained by space. In this context, it is urgent to seek scientific ways to improve the production efficiency in limited space. It is one of the effective ways to enable the industry to improve production efficiency. In many new aquatic varieties, the growth rate is usually one of the important target breeding traits.

As the single highest yield of cultured shellfish in China, Ruditapes philippinarum is distributed in the major sea areas of China's north and south, with an annual output of more than 4 million tons, accounting for 90% of the world's total output. The main new varieties of breeding are Zebra clam, white zebra clam, and Zebra clam 2. A total of 600 individuals were selected from a wild population in Shihe, Dalian, Liaoning Province, and the results showed that the shell length and total wet weight of 12 months increased by 10.6% and 19.5%, respectively, after 4 successive generations of population selection withthe aim of shell color and growth rate. At present, the research on the new R. philippinarum species Zebra clam 2 variety primarily focuses on the influence of external environmental stress on metabolism and physiology, the comparison of breeding mode, the juvenile sand diving behavior, and ammonia nitrogen tolerance, etc. There are no reports on the comparative analysis of dietary metabolism, physiology, and energy budget between the two.

In order to clarify the differences in feeding metabolic physiological processes and energy distribution strategies between Zebra clam 2 and unselected group, three sizes (shell length 40–45 mm, 35–40 mm and 30–35 mm, respectively) of Zebra clam 2 and unselected group were chosen as experimental subjects in July 2023. In Sanggou Bay, Rongcheng City, Shandong Province, the metabolic and physiological processes of food intake between the two groups were studied by the field flow method. The energy budget equation was constructed based on basic physiological parameters such as water filtration rate, ammonia discharge rate, and oxygen consumption rate, and the differences in energy distribution modes were compared and analyzed.

The experimental results showed that the filtration rate and assimilation efficiency of the three specifications of Zebra clam 2 were higher than those of the unselected group, but the differences were not significant (P>0.05). The oxygen consumption rate of medium-sized Zebra clam 2 was significantly higher than that of the unselected group (P<0.05), while that of small-sized Zebra clam 2 was significantly lower than that of the unselected group (P<0.05). The ammonia excretion rate of the medium and small size Zebra clam 2 was significantly higher than that of the unselected group (P<0.05). In terms of energy budget, compared with the unselected group, the intake energy of large, medium and small size Zebra clam 2 increased by 45.22%, 18.60% and 21.40%, the absorption energy increased by 54.90%, 18.60% and 29.67%, and the growth power increased by 57.65%, 17.43% and 31.79%, respectively. This indicates that Zebra clam 2 of the same size showed higher energy intake (filtration rate) and slightly higher absorption efficiency than the unselected group. Although the energy consumption (oxygen consumption and excretion energy) of Zebra clam 2 of the same size was slightly higher than that of the unselected group, the proportion was relatively small (<10%), so Zebra clam 2 showed a higher growth power and led to a faster growth rate due to its higher energy intake. The results of this study provide basic data for further understanding of the physiological characteristics of Zebra clam 2 and for evaluating the breeding capacity of this new variety.

我国是世界海水贝类养殖第一大国,近几十年来养殖产量和规模增长迅猛,2023 年,养殖产量达到 1 646.06 万 t,养殖面积达 1 357 530 hm2农业农村部渔业渔政管理局等,2024)。作为海水养殖的支柱产业,贝类养殖在促进沿海地区经济发展、拓宽渔民增收渠道、提高水体透明度、缓解水体富营养化、应对气候变化等方面做出了重要贡献(Kaspar et al,1985; Soto et al,1999; 蒋增杰等,2022; 唐启升等,2022)。但总体来看,目前我国的海水贝类养殖产业仍然属于劳动密集型和数量效益型产业,养殖产量的提升更多依赖于养殖面积的扩大。近 20 年(2004—2023 年),我国海水贝类养殖面积扩大了 28.11%,支撑了养殖产量 54.19%的增长(农业农村部渔业渔政管理局等,2024)。随着滨海旅游、海洋交通运输等多种用海产业对海洋空间资源竞争的日趋激烈,海水养殖受空间约束日趋加剧,在这样的背景下,亟需寻求提升有限空间生产效率的科学途径。良种赋能产业进而提升生产效率是有效途径之一。据全国水产原种和良种审定委员会数据显示,截至 2024 年,我国已审定的水产新品种达到 306 个,新品种的不断涌现,充分展现出我国水产种业蒸蒸日上的发展态势。在诸多的水产新品种中,生长速度快通常是重要的目标选育性状之一。
菲律宾蛤仔(Ruditapes philippinarum),属于广温、广盐性品种,分布广泛,年产量超 300 万 t,是我国养殖贝类中单种产量最高的种类。目前菲律宾蛤仔新品种主要有斑马蛤(新品种登记号 GS-01-005-2014)、白斑马蛤(新品种登记号 GS-01-009-2016)、斑马蛤 2 号(新品种登记号 GS-01-007-2021)。其中,斑马蛤 2 号以壳色和生长速度作为选育目标,基于辽宁大连石河野生群体中选出的 600 只个体,经过连续 4 代的群体选育技术培育而成。经过 12 个月养殖后,与未选育群体相比较,斑马蛤 2 号贝壳长提高了 10.6%,湿重提高了 19.5%(闫武喜等,2022)。目前对菲律宾蛤仔新品种斑马蛤 2 号的研究主要集中在外界环境胁迫对代谢生理的影响(周红等,2023)、养殖模式的对比(田园等,2021)、幼贝潜沙行为(马倩颖等,2021)、氨氮耐受性(Ma et al,2022)等方面,但对于斑马蛤 2 号与未选育群体摄食代谢生理及能量收支对比分析的研究尚未见报道。得益于生长速度快的优点,斑马蛤 2 号在缩短养殖周期、提高经济效益等方面发挥了积极作用,但展现出“生长速度快”这一优势的内在机理尚不明确。基于此,本研究采用现场流水实验方法结合生理能量学测定技术,对比分析 3 种规格斑马蛤 2 号与未选育群体摄食代谢生理以及能量分配策略的差异,深入解析斑马蛤 2 号生长更快的内在机理,研究结果可为后续科学评估新品种的养殖容量、进而充分发挥新品种的生长优势提供基础数据。
1 材料与方法
1.1 实验材料
实验所用的菲律宾蛤仔新品种斑马蛤 2 号和未选育群体均取自辽宁省大连市庄河海域。采集大(L)、中(M)、小(S)3 种规格(表1)各 50 只实验用贝运送到山东省荣成市桑沟湾楮岛码头实验室,清除壳表面的污物和附着生物后,暂养 3 d,暂养期间剔除死亡和状态不好的蛤仔。暂养结束后,每种规格挑选出 9 个活力较好的个体用于后续实验。
1斑马蛤 2 号与未选育群体生物学参数
Tab.1Biological parameters of Zebra clam 2 and unselected group
注:同一列同一规格中不同字母表示组间差异显著(P<0.05),下同。
Notes: Different letters in the same column and the same size indicate significant differences between groups (P<0.05) , the same below.
1.2 实验方法
2023 年 6 月 29 日至 7 月 4 日,摄食代谢生理实验采用现场流水实验系统,搭建方法参考李伟伟等(2024),实验水源来自自然海区。实验期间,于每天 10:00、12:00、14:00、16:00 用便携式水质参数分析仪(YSI WTW,美国)测定实验所用海水的温度(T)、盐度(S)、溶解氧(DO)和 pH。实验期间,海水盐度变化范围为 30~31,pH 变化范围为 8.02~8.27,溶解氧浓度变化范围为 7.30~8.52 mg/L,海水温度变化范围为19.95~22.83℃。
1.2.1 滤水率测定
本实验共设置 12 个流水槽,实验过程中水流流速控制在 180~220 mL/min 以内。待流速稳定后,将贴好标签的 9 个实验用贝放入流水槽中适应 1 h,第 4、8、12 个流水槽不放贝,作为空白对照组。观察流水槽中实验贝类状态,以实验用贝开口(表征实验用贝正常摄食)作为实验开始的标志。实验持续 3 h,在第 1、2、3 小时分别从每个流水槽出水口接水样 100 mL,通过便携式颗粒计数器 PAMAS(测定粒径范围为 2~200 μm,S4031GO,德国)测量所取水样中的颗粒物数量。在实验的第 2 小时,从入水口取水样 1 000 mL,采用直径为 47 mm 孔径 0.7 μm 的 Whatman GF/F 玻璃纤维滤膜(在马弗炉中经 450℃灼烧 6 h 并称重 W0)抽滤,抽滤后用 0.5 mol/L 的甲酸铵冲洗。使用锡纸将抽滤之后的滤膜包裹,保存在–20℃冰箱。对于样品处理,先将滤膜在 60℃ 烘箱中烘干约 48 h 至恒重(W60),测定样品总干重(TPM)。之后置于马弗炉 450℃灼烧 6 h 后称重(W450),用于计算样品的无灰分重量(POM)。
1.2.2 耗氧率和排氨率测定
实验设置 10 个 1 L 的圆形透明密封玻璃容器作呼吸室,盖子上有 2 个进出水阀门,进水阀门连接分流管,用小水泵从滤水实验整理箱中抽水,经过分流管接到每个呼吸室内,保证呼吸室内可以形成流水状态。将贴好标签的 9 个实验用贝放入呼吸室中,为实验组;1 个呼吸室不放实验用贝,为对照组。开始实验前,打开水泵和呼吸室的进出水阀门,使呼吸室内处于流水状态,待实验用贝在流水状态下驯化至开口后关闭进水泵,拧紧呼吸室的进出水阀门,静水状态下开始耗氧实验。采用十通道实时溶氧测定仪(PreSens Precision Sensing,德国)实时监测每个呼吸室溶解氧浓度,以“呼吸室内溶解氧下降了初始溶解氧的 10%”为结束耗氧实验的标准(为避免对实验用贝造成溶氧胁迫,呼吸室内溶氧含量不能低于 5 mg/L)。实验结束后,每个呼吸室内取 100 mL 水样,用玻璃纤维滤膜(孔径为 0.45 μm,直径为 47 mm)过滤除去浮游生物,在过滤后的水样中加入 2~3 滴三氯甲烷以隔绝空气,置于–20℃冰箱保存,用于氨氮的测定。上述所采集水样按照《海洋调查规范》(GB/T12763-2007)开展样品测定。其中,亚硝酸盐使用重氮–偶氮法来测定,铵盐采用次溴酸钠氧化法进行测定。
1.2.3 粪便收集
在滤水实验完成后,保持流水系统的流水状态直至流水槽中有贝类粪便产生,用巴氏吸管吸取流水槽中粪便(黑色、颗粒状固体)至聚乙烯瓶中,抽滤到预先灼烧并称重(W0)的 Whatman GF/F 玻璃纤维滤膜(直径为 47 mm,孔径为 0.7 μm)上,用 0.5 mol/L 的甲酸铵冲洗,过滤后的滤膜使用锡纸包裹,置于–20℃冰箱保存。后续粪便样品先置于 60℃ 烘箱烘干 48 h 至恒重(W60),测定样品总干重(TPM)。之后置于马弗炉 450℃煅烧 6 h 后称重(W450),用于计算样品的无灰分重量(POM)。
1.2.4 生物学参数测定
实验结束后,测量所用实验贝类生物学参数。用游标卡尺测量实验用贝壳长、壳宽、壳高;用电子天平称量总湿重、软组织湿重,随后将所称壳与软组织放置于 60℃烘箱中,烘干约 72 h 至恒重,称量壳干重和软组织干重。
1.3 实验指标的测定与计算
滤水率 (CR,L/h)=FR×C0-C1/C0
(1)
式中,FR 为流水槽的流速(L/h),C0C1 分别为对照组和实验组水体中颗粒物浓度;
耗氧率 OR,mgO2/h=DO0-DOt×V/t
(2)
式中,DO0 和 DOt 分别为实验结束时对照组和实验组水中溶解氧浓度(mg/L);V 为密封槽的体积(L);t 为实验持续时间(h);
排氨率 (RE,mgN/h)=Nt-N0×V/t
(3)
式中,N0Nt 分别为实验结束时对照组和实验组水中的氨氮浓度(mg/L);V 为密封槽的体积(L);t 为实验持续时间(h);
同化效率 (AE,%)=(F-E)/[(1-E)×F]( Conover,1966 )
(4)
式中,F 为颗粒物无灰分干重/食物总干重;E 为粪便无灰分干重/粪便总干重。
组织干重标准化:
Ys=Ws/Web×Ye( Wang et al, 2015 )
(5)
式中,Ys 为生物软组织干重标准化后的生理参数; Ws 为标准重量(1 g);We 为测得的动物组织干重(g); Ye 为未标准化的生理参数;b 为 0.67。
生长余力(SFG,P)计算公式如下:
P=A-(R+U)
(6)
A=C×AE
(7)
C=CR[L/(hg)]×POM(mg/L)×23(J/mg)
(8)
式中,C 为摄食能(ingested energy);A 为吸收能(absorbed energy);R 为耗氧能(respired energy),其中 1 mgO2=14.25 J;U 为排泄能(excreted energy),其中 1 mgNH4+-N=24.93 J(Slobodkin et al,1961; Widdows et al,1979; Gnaiger,1983)。
1.4 数据分析
实验数据分析使用 SPSS 26 软件。通过单因素方差分析法(one-way ANOVA)对实验数据进行方差分析,并进行 Duncan 多重比较和方差齐性检验,以 P<0.05 作为差异显著水平。描述性统计值采用平均值±标准差(Mean±SD)表示。使用 GraphPad Prism 7.0 软件作图。
2 结果与分析
2.1 斑马蛤 2 号和未选育群体滤水率与吸收效率对比
斑马蛤 2 号与未选育群体单位干重滤水率和同化效率如图1所示,大、中、小 3 种规格斑马蛤 2 号的滤水率均高于未选育群体,分别提高了 10.59%、 4.29%和 8.71%,但差异不显著(P>0.05);与未选育群体相比,大、中、小 3 种规格斑马蛤 2 号的同化效率均有不同程度的提升,提升幅度分别为 6.07%、0.16% 和 5.07%,但差异不显著(P>0.05)。
2.2 斑马蛤 2 号和未选育群体耗氧率与排氨率对比
斑马蛤 2 号与未选育群体单位干重耗氧率和排氨率如图2所示,大、中规格斑马蛤 2 号的耗氧率均高于未选育群体,分别提高了 22.20%和 40.00%,其中,中规格差异显著(P<0.05),小规格斑马蛤 2 号耗氧率较未选育群体降低了 25.53%,差异不显著(P>0.05);与未选育群体相比,大、中、小 3 种规格斑马蛤 2 号的排氨率均有不同程度提升,提升幅度分别为 6.89%、44.83%和 63.79%,其中在中、小规格中差异显著(P<0.05)。
2.3 斑马蛤 2 号和未选育群体能量收支对比
斑马蛤 2 号和未选育群体能量收支结果见表2。从能量摄入角度来看,大、中、小规格的斑马蛤 2 号摄食能较未选育群体均有一定程度的提升,分别提升了 45.22%、18.60%和 21.40%,吸收能分别提升了 54.90%、18.60%和 29.67%;从能量消耗角度来看,大、中规格斑马蛤 2 号耗氧能较未选育群体分别提高了 25.00%和 41.88%,而小规格降低了 26.78%;大、中、小 3 种规格斑马蛤 2 号的排泄能较未选育群体分别提高了 6.02%、44.97%和 62.48%;二者生长余力在大、中、小 3 种规格下均显示出显著差异,斑马蛤 2 号较未选育群体分别提升了 57.65%、17.34%和 31.79%。
1斑马蛤 2 号与未选育群体单位干重滤水率(A)和同化效率(B)对比
Fig.1Comparison of clearance rate (A) and absorption efficiency (B) per unit dry weight between Zebra clam 2 and unselected population
图中标有相同字母的数据表示 2 个群体之间差异不显著(P>0.05),下同。
Data with the same letter mean no significant differences between two groups (P>0.05) , the same below.
2斑马蛤 2 号与未选育群体单位干重耗氧率(A)和排氨率(B)对比
Fig.2Comparison of oxygen consumption rate (A) and ammonia excretion rate (B) per unit dry weight between Zebra clam 2 and unselected population
2斑马蛤 2 号与未选育群体能量收支/[J/(h·g)]
Tab.2Energy budget of Zebra Clam 2 and unselected group/[J/ (h·g) ]
3 讨论
在相同的环境条件下,生物主要通过 3 种不同的机制提高其生长速度,对应着 3 种不同的模型加以解释:第 1 种模型是增加获取模型(increased acquisition model),该模型强调个体具有更快的摄食速度,可以增加单位时间的食物摄入量。这种行为会导致在吸收效率相近的情况下可以获得更多的能量,强调了能量获取过程。第 2 种模型是修正后的分配模型(modified allocation model),它表明更快的生长可能是分配给生长的能量比例更大的结果,但这也是以牺牲其他能量需求过程为代价的,例如身体维护,该模型强调了能量分配过程。第 3 种模型是代谢效率模型(metabolic efficiency model),它强调生长速度快可能是因为生长效率的提高或者是生长的新陈代谢成本降低,从而提高了生长速度(Bayne et al,1999b)。这 3 种模型主要从个体生理性状(摄食率、相关代谢成本、生长成本)解释了导致生长速率差异的不同原因。这不仅适用于双壳软体动物(Hawkins et al,1996; Bayne et al,1999a),对其他类群也同样适用(Present et al,1992; Rist et al,1997)。
从能量摄入方面来看,本研究中,3 种规格的斑马蛤 2 号滤水率均大于未选育群体,且不同规格之间的提升也存在差异。目前研究表明,滤食性贝类的摄食机制主要依赖于 2 种方式:粘液纤毛机制与水动力学机制。无论贝类通过哪种摄食机制进行摄食,鳃及其上着生的纤毛类型和唇瓣都会对滤水率产生影响。例如,已有研究发现,不同品种牡蛎生长速度与鳃和唇瓣的比例有关,拥有更大滤水率和生长速度的品种也具有更大的鳃与唇瓣比(Honkoop et al,2003)。对于单位软组织干重而言,斑马蛤 2 号与未选育群体 3 种规格个体的滤水率均呈随着规格增大而减小的趋势,这与匡世焕等(1996)高露姣等(2006)黄洋等(2014) 对不同规格栉孔扇贝(Azumapecten farreri)、巨牡蛎(Crassostrea sp.)、尖紫蛤(Sanguinolaria acuta)的滤水率测定结果一致。已有研究表明,较小个体滤水率大于较大个体,是由于代谢需求的提高(Sylvester et al,2005),以及小个体鳃具有更高的颗粒物收集效率(Mardones et al,2024)。而不同规格斑马蛤 2 号与未选育群体滤水率对比的差异性,例如大规格斑马蛤 2 号滤水率较未选育群体提升 10.59%、中规格提升 4.29%、小规格提升 8.71%。推测这和鳃与唇瓣比会随着贝生长月龄的增加而改变有关。但仍需后续实验加以验证。同化效率表征了动物对营养物质的消化吸收能力,是贝类能量学研究中的重要参数之一,在个体生长发育过程中起到决定性作用。在本研究中,3 种不同规格的斑马蛤 2 号与未选育群体分别对比来看,斑马蛤 2 号的同化效率均高于同规格未选育群体。其高低除了与周围环境中食物种类和浓度有关(Hawkins et al,1984; Bayne et al,1987)外,最主要由消化酶活性所控制(MacDonald et al,1998)。已有的研究结果显示,具有较高消化酶活性的群体一般具有较高的生长速度(邓岳文等,2008; 王庆恒等,2010)。另外,也有研究表明,高摄食率会导致贝类胃容量的增加,使得食物在胃中停留时间增加,从而使同化效率增加(Navarro et al,1992),这与本研究中摄食率的结果一致。王俊等(2000)研究表明,同化效率受贝类个体大小的影响并不明显。本研究结果中,斑马蛤 2 号和未选育群体 3 种规格的同化效率在 37%~47%之间,同化效率变化与实验贝规格大小关系并不明显,这与上述研究结果一致。
从能量消耗角度来看,呼吸和排泄是贝类主要的消耗能量途径。已有研究证实,双壳贝类种间和种内基础代谢率的差异与膜磷脂不饱和性有关,且不同双壳贝代谢与膜磷脂的不饱和性呈正相关(Pernet et al,2006、2007)。本研究中,除了小规格的两个品种的耗氧率外,同种规格斑马蛤 2 号的排氨率和耗氧率均大于未选育群体,这说明同种规格斑马蛤 2 号均较未选育群体具有较高的代谢,这表明斑马蛤 2 号较后者具有更高的膜磷脂不饱和性。由于基础代谢的很大一部分与膜连接过程有关,线粒体质子泄露、Na+ 和 Ca2+ 循环加在一起约占标准代谢率的一半(Rolfe,1997), Hulbert 等(1999、2000)研究发现,膜作为代谢的起搏器,膜磷脂可能通过影响膜结合酶的分子活性在确定不同物种间代谢率方面发挥作用。同一群体 3 种不同规格的单位体重耗氧率均随规格增大而减小,这与对不同规格其他双壳贝类耗氧率的研究结果一致(王芳等,1997; 赵文等,2011)。姜祖辉等(1999)指出,这种现象可能与水生生物在生长过程中组织和器官的比例变化有关。维持生命的关键组织和器官(如肾脏、肝脏等)代谢率高于非关键组织和器官(如肌肉、脂肪等)。随着生物生长的过程,关键器官的比例下降,而肌肉和脂肪的比例逐渐增加,这将会导致个体单位软体干重的耗氧率随体型增大而降低。与耗氧率相同,滤食性贝类排氨率同样受多种因素的影响。在本研究结果中,大、中、小 3 种规格的未选育群体和斑马蛤 2 号排氨率分别为 0.043、0.029、0.058 mg/(h·g)和 0.046、0.042、0.095 mg/(h·g),可以看出,二者单位体重排氨率都随着规格增大而先减小后增大,这与对不同规格栉孔扇贝、菲律宾蛤仔、中国蛤蜊(Mactra chinensis Philippi)排氨率的研究结果并不一致(王芳等,1997; 赵文等,2011)。但本研究中,2 种蛤排氨率介于 0.029~0.095 mg/(h·g)之间,这与姜祖辉等(1999) 对菲律宾蛤仔的研究结果[0.055~0.127 mg/(h·g)]和柴雪良等(2005)对美国硬壳蛤(Mercenaria mercenaria)的研究结果[(33.908±4.686)μg/(g·h)]相近。不同规格斑马蛤 2 号与未选育群体间代谢率的提升也存在一定差异,包括小规格斑马蛤 2 号耗氧率甚至低于未选育群体。推测不同物种间膜磷脂不饱和性很有可能与物种生长月龄也存在一定相关性,需要后续的研究来证明。
生长余力是动物摄食的食物能量与其利用消耗及损失的能量之差,是可以反映贝类生长的生理能量的指标(Newell,1980)。本研究中,同种规格的斑马蛤2 号生长余力均显著高于未选育群体(P<0.05),大、中、小规格分别提升了 57.65%、17.34%和 31.79%。在能量收支方面,同种规格斑马蛤 2 号较未选育群体表现出较高的能量摄入(滤水率)和略高的吸收效率。虽然同种规格的斑马蛤 2 号能量消耗(耗氧能+排泄能)均略高于未选育群体,但占比较小(<10%),所以斑马蛤 2 号较未选育群体具有较高的能量摄入,表现出了较高的生长余力。不同规格的斑马蛤 2 号和未选育群体对比结果显示,二者生长余力均随着规格增大而减小,这说明小规格个体明显比大规格个体长得更快。这与常亚青等(1998) 对皱纹盘鲍(Haliotis discus Hannai)的研究结果一致。但 3 种规格的蛤生长余力均占比较高,这说明实验贝类均处于快速生长阶段,将吸收的大部分能量用于个体生长和繁殖。
本研究基于现场流水系统,结合便携式颗粒计数器和连续氧气监测技术,从个体生理能量学层面对不同规格斑马蛤 2 号和未选育群体进行对比研究。结果表明,与未选育群体相比,斑马蛤 2 号呈现较高生长速度的原因是更多的食物摄入导致其具有更高的能量摄入,属于上述提及的第 1 种类型——增加获取型。已有研究表明,双壳动物鳃纤毛活动依赖于纤毛兴奋性,神经递质(GABA、血清素)与纤毛的兴奋性有关联(Aiello,1970; Jiang et al,2019)。这可能是斑马蛤 2 号较未选育群体滤水率提高的原因之一,尚需进一步结合代谢组学等系统生物学技术深入研究内在机制。
1斑马蛤 2 号与未选育群体单位干重滤水率(A)和同化效率(B)对比
Fig.1Comparison of clearance rate (A) and absorption efficiency (B) per unit dry weight between Zebra clam 2 and unselected population
2斑马蛤 2 号与未选育群体单位干重耗氧率(A)和排氨率(B)对比
Fig.2Comparison of oxygen consumption rate (A) and ammonia excretion rate (B) per unit dry weight between Zebra clam 2 and unselected population
1斑马蛤 2 号与未选育群体生物学参数
Tab.1Biological parameters of Zebra clam 2 and unselected group
2斑马蛤 2 号与未选育群体能量收支/[J/(h·g)]
Tab.2Energy budget of Zebra Clam 2 and unselected group/[J/ (h·g) ]
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