团头鲂两个生长阶段适宜蛋白/脂肪比的需要量

为了在相同配方体系下研究团头鲂两个生长阶段对饲料中蛋白/脂肪比的需要量,以初均重为(35.07±0.45)g(幼鱼)、(101.65±1.82)g(育成鱼)两个阶段的团头鲂为实验鱼,以秘鲁鱼粉、酪蛋白、大豆磷脂、豆油等原料配制半纯化饲料,在蛋白质26.93%~35.63%、脂肪10.24%~3.35%范围内,设置蛋白/脂肪比浓度分别为2.63、3.20、4.07、5.33、7.25和10.64共6组饲料。分别在池塘网箱养殖85和56 d,每组实验鱼设置4个平行。结果发现,随着饲料蛋白/脂肪比水平的增加,两个阶段的团头鲂体质量特定生长率(SGR)、蛋白质沉积率(PDR)、能量保留率(ERR)总体均呈现先上升后下降的趋势,均在饲料蛋白/脂肪比为5.33组达到最高;饲料系数(FCR)则呈先下降后上升的趋势,且均在饲料蛋白/脂肪比为5.33组达到最低。分别以实验鱼特定生长率(SGR)、饲料系数(FCR)、蛋白质沉积率(PDR)及能量保留率(ERR)作为评价指标,经过回归分析可知,幼鱼阶段团头鲂对饲料中蛋白/脂肪比需要量为6.09~7.58,适宜蛋白质水平为32.83%~33.98%、脂肪水平为4.48%~5.39%;在日均摄食量为5.06 g/100 g体质量的条件下,团头鲂幼鱼对饲料蛋白质每日需要量为1.66~1.72 g/100 g体质量,对饲料脂肪每日需要量为0.23~0.27 g/100 g体质量。育成鱼阶段团头鲂对饲料中蛋白/脂肪比需要量为4.03~4.34,适宜蛋白质水平为30.19%~30.72%、脂肪水平为7.07%~7.49%。在日均摄食量为3.61 g/100 g体质量的条件下,团头鲂育成鱼对饲料蛋白质每日需要量为1.09~1.11 g/100 g体质量,对饲料脂肪每日需要量为0.26~0.27 g/100 g体质量。     

饲料锌对团头鲂幼鱼生长性能、血清生化指标和抗氧化功能的影响

以酪蛋白和明胶为蛋白源,七水硫酸锌(Zn SO4·7H2O)为Zn源,分别配制成7种Zn含量(7.4 mg/kg、20.3 mg/kg、32.1 mg/kg、51.0 mg/kg、84.4 mg/kg、169.7 mg/kg、332.4 mg/kg)的半纯化饲料,投喂初始体重为(3.6±0.1)g团头鲂(Megalobrama amblycephala)12周,考察Zn对团头鲂幼鱼生长性能、血清生化指标和抗氧化功能的影响,确定团头鲂幼鱼对饲料Zn的需要量。结果表明,随着饲料Zn含量增加,团头鲂增重率、特定生长率和全鱼Zn含量呈先增加后稳定的趋势;全鱼水分含量显著降低(P0.05),粗蛋白含量显著增加。饲料Zn含量对团头鲂饲料系数无显著影响。饲料中添加Zn显著影响血清总蛋白、尿素氮、高密度脂蛋白胆固醇、总胆固醇以及甘油三酯含量,而对血清白蛋白含量和碱性磷酸酶活性无显著影响。随着饲料中Zn含量的增加,团头鲂肝丙二醛含量显著降低(P0.05),而肝过氧化氢酶和超氧化物歧化酶活性在各处理间均无显著差异。折线回归分析表明,团头鲂幼鱼(体重3.6~26.7 g)获得最佳生长时对饲料Zn需要量为32.6 mg/kg,获得最大鱼体Zn含量时Zn的需要量为47.6 mg/kg。本研究旨在确定团头鲂幼鱼对饲料中Zn的需要量,为配制团头鲂高效环保饲料提供科学依据。     

团头鲂对饲料中Zn的需求量

为了研究团头鲂对饲料中Zn的需要量,以平均体质量50 g的团头鲂为实验对象,采用半纯化饲料,以ZnSO4·H2O为锌源,设置Zn添加量分别为0、68、137、206、275 mg/kg(饲料中Zn总量为22.85、98.07、164.00、235.43、307.96 mg/kg)共5个Zn含量梯度,每个实验组设4个平行,在池塘网箱中养殖43 d。经过回归拟合分析,饲料中Zn添加量、饲料中Zn总量与团头鲂特定生长率、饲料系数、蛋白质沉积率、脂肪沉积率的关系,得到团头鲂对饲料中无机Zn补充量为155.86~161.25 mg/kg,对饲料总Zn需要量为184.85~190.39 mg/kg;在日均摄食量为5.12 g/100 g体质量下,团头鲂对饲料Zn日需求量为0.798~0.825 mg/100 g体质量,对饲料总Zn日需要量为0.946~0.974 mg/100 g体质量。饲料中Zn含量对团头鲂的成活率、肥满度、内脏指数、鳞片重/体质量、体质量/体长、脊椎骨重/体质量无显著影响(P0.05)。饲料中Zn含量对团头鲂的脊椎骨长/体长有显著影响(P0.05);饲料中Zn的补充,有利于团头鲂脊椎骨的生长。     

青鱼、团头鲂的低动物蛋白饲料配制及高产饲养技术

为降低饲料成本,经过多次生产性试验,采用低动物蛋白饲料饲养青鱼、团头鲂,可获得亩净产1000公斤的产量,其饲料质量控制的主要指标为:粗蛋白28～30%(青鱼),25～30%(团头鲂);粗脂肪4.5%(青鱼),4.5～6.0%(团头鲂);无氮浸出物35%(青鱼),38～33%(团头鲂);粗纤维8%(青鱼),7.5%(团头鲂);磷0.57%;钙0.68～0.64%;维生素为必需添加物,促生长剂亦有助于加速生长。此外,对饲料的配制和加工,以及饲养技术要点亦作了论述。     

饲料中脂肪的含量对团头鲂鱼种生长的影响

本文报道了团头鲂鱼种在饲料中的蛋白质、糖、维生素和无机盐等保持适宜含量的条件下,不同脂肪含量对团头鲂鱼种生长影响的试验结果,试验所用的脂肪为新鲜的豆油。结果表明,团头鲂鱼种饲料中脂肪适宜含量为 2～5％,最适含量为3.6％左右。     

团头鲂饲料中最适蛋白质含量

本文采用直线回归和抛物线回归两种方法求出最适点作为团头鲂饲料蛋白质最适需要量的范围,即21.05-30.83％。     

两种水温条件下团头鲂对7种蛋白源饲料表观消化率的比较

采用由30%待测蛋白源饲料原料和70%基础饲料组成的试验饲料,以三氧化二钇(Y_2O_3)作外源指示剂,添加量为0.05%,以平均体重(34.38±1.06)g的团头鲂(Megalobrama amblycephala)幼鱼作研究对象,在30℃和25℃两种水温条件下比较研究其对鱼粉(FM)、豆粕(SBM)、菜粕(RSM)、棉粕(CSM)、酵母浸粉(YEF)、肉骨粉(MBM)和花生粕(PNM)7种蛋白源饲料原料的干物质(DM)、粗蛋白(CP)、总能(GE)、总氨基酸(TAA)及必需氨基酸(EAA)的表观消化率。结果显示:水温30℃时,酵母浸粉的干物质、总能、粗蛋白和必需氨基酸的表观消化率最高;水温25℃时,原料干物质和总能的表观消化率最高的为鱼粉,粗蛋白、必需氨基酸和总氨基酸的表观消化率最高的为豆粕。在两个水温下,原料干物质、粗蛋白、总氨基酸和必需氨基酸的表观消化率最低的均是肉骨粉,总能的表观消化率最低的是棉粕。在30℃时团头鲂对蛋白源饲料原料各营养成分的表观消化率高于25℃时,且酵母浸粉在两个水温下各营养成分的消化率差异显著(P0.05)。在30℃时,酵母浸粉的各养分表观消化率较高,但其氨基酸平衡性较差,需适量添加蛋氨酸,满足团头鲂对氨基酸的需求;在25℃时,豆粕和鱼粉各养分表观消化率较高,可作为团头鲂饲料的优质蛋白源饲料原料。肉骨粉在两个水温下均表现出最低表观消化率,需搭配其他饲料适量使用。     

池塘饲养团头鲂的研究

从饵料选择、饲养密度和池塘水面3个方面对北疆地区池塘主养团头鲂进行了研究。试验结果表明:试验所选A和B两种饲料都能很好地促进团头鲂的生长,团头鲂的平均相对增长率分别为195.70%和187.70%;团头鲂在饲养密度为325.6~597.0 kg/hm2时生长较快;在水面较大的池塘中,团头鲂呈现出较好的生长势头。     

青鱼、草鱼、团头鲂的肌肉及有关天然饲料的生化组成分析

本文主要阐述不同生长阶段的青鱼、草鱼、团头鲂的肌肉及与这三种鱼食性有关的天然饲料生化组成。分析结果表明,三种鱼的肌肉中以水分含量最高,蛋白质、脂肪、灰分、醣依次减少。三种鱼处在不同生长阶段(即夏花、一龄鱼、二龄鱼和食用鱼),其肌肉生化组成特点是:水分随鱼体生长逐渐下降,呈显著的负相关,相关系数分别为青鱼r=-0.88,草鱼r=-0.94,团头鲂r=-0.93;脂肪含量随鱼体生长逐渐增加,青鱼和团头鲂呈显著的正相关,相关系数分别为r=0.96和r=0.94,雨草鱼的相关系数r=0.47,不显著;蛋白质、鱼、灰分含量的交幅不大,趋于相对稳定。三种鱼的肌肉蛋白质氨基酸组成基本相同,必需氨基酸含量(干重计)为氨基酸总量的50％以上,以食用鱼阶段相比较,青鱼的必需氨基酸含量占51.5％,草鱼和团头鲂的必需氨基酸分别占氦基酸总量的50％和46.7％,均可称得上高质量的完全蛋白质。青鱼的天然饲料(干物汁),螺蛳的蛋白质含量为53.18％,脂肪5.0％,醣17.3％;黄蚬的蛋白质含量为48.68％,脂肪10.15％,醣31.5％;草鱼的天然饲料(干物汁),宿根黑麦草的蛋白质含量为31.62％,脂肪6.43％,醅38％;苦草的蛋白质含量为18.89％,脂肪2.79％,醣36.22％。在这些天然饲料中,必需氨基酸的组分种类齐全,含量占氨基酸总量的50％左右;饲料的能量蛋白比(C/P比),螺蛳为61.4,黄蚬为84.64％,宿根黑麦草为107.13％,苦草为129.96。实验证明,这四种天然饲料的蛋白质,脂肪,醣的含量和C/P比,与青鱼、草鱼、团头鲂的营养需求相适应,可称为优良的天然饲料。本研究为我国主要养殖鱼类的营养学研究及鱼用饲料的开发提供了基础理论依据。     

鲤鱼种豆粉饵料中 蛋氨酸的添加量

为测定豆粉基本饲料中仅添加蛋氨酸能否满足鲤鱼种的营养需要量以及增加量是否能进一步提高豆粉的营养价值，进行了6周的投饵试验。试验饵料中添加的氨基酸组成为：(1)必需氨基酸混合物中不含蛋氨酸；(2)必需氨基酸混合物中含低含量(0．25%)或高含量(0．50％)的蛋氨酸；(3)非必需氨基酸混合物；     

Dietary essential amino acids and heat increment in rainbow trout (Oncorhynchus mykiss)

Oxygen consumption attributable to apparent heat increment (AHI) was measured in relation to varying essential amino acid proportions (EAA) infused into rainbow trout,Oncorhynchus mykiss (250–450 g), induced to swim at 1 BL s^–1. Five diets, mimicking EAA concentrations in trout whole body protein, deficient in the branched chain amino acids (isoleucine, leucine and valine), containing unbalanced proportions of EAAs and supplying lysine in excessive and limiting proportions, were tested. Following infusion of the experimental diets, a significant increase in oxygen consumption was observed. Changes in plasma EAAs following infusion paralleled the time course of AHI (i.e., oxygen consumption). AHI represented the equivalent of 15–32% of the gross energy intake depending on dietary EAA composition. Diets supplying EAAs similar to trout whole body protein and limiting in lysine produced the lowest AHI values, indicating efficient utilization of dietary amino acids. Higher AHI values were associated with diets deficient in the branched chain amino acids and diets supplying lysine in excess. Duration of elevated metabolism was independent of both dietary composition and energy intake. Different proportions of EAAs in the diet can increase the energy expended as AHI. In an attempt to reduce the energy liberated as AHI, attention must be paid to the quality, quantity and balance of dietary EAAs.     

Changes in proximate and amino acid composition during early development of two Australian Percichthyid fish, Macquarie perch, Macquaria australasica Cuvier, and trout cod, Maccullochella macquarensis (Cuvier)

In the present paper, the results of a study on changes in the proximate and amino acid composition of the eggs and larvae of two Australian native Percichthyid fish, Macquarie perch, Macquaria australasica Cuvier, and trout cod, Maccullochella macquarensis (Cuvier), are presented. The stages of development studied were unfertilized and fertilized eggs, newly hatched larvae, and post-yolk-sac larvae (in Macquarie perch only). In Macquarie perch, significant changes in moisture content occurred throughout development, but this was not so in trout cod. The protein content (per cent dry weight) in Macquarie perch larvae only decreased significantly after hatching (P < 0.05). On the other hand, the total lipid (by dry weight) increased significantly during this transformation (P < 0.05), and decreased significantly in yolk-sac-resorbed larvae. In trout cod, the protein and lipid content did not change significantly up to hatching. The ash content increased significantly in newly hatched and yolk-sac-resorbed larvae of both species. The total amino acid contents of unfertilized eggs, fertilized eggs, newly hatched larvae and yolk-sac-resorbed larvae of Macquarie perch and trout cod were 5752, 4652, 3696 and 2723 μmol g^?1 (dry weight), and 4688. 3448 and 2329 μmol g^?1, respectively. In the amino acid pool in Macquarie perch, the essential amino acids (EAAs) leucine, isoleucine and valine, and the non-essential amino acids (NEAAs) alanine, aspargine and glutamate occurred in the greatest quantities in non-fertilized eggs, and the cysteine content was the smallest. In Macquarie perch, five out of nine EAAs (i.e. isoleucine, leucine, lysine, threonine and valine) and six out of eight NEAAs (i.e. alanine, asparagine, glutamate, glycine, proline and serine) decreased significantly (P < 0.05) from one developmental stage to the other. In trout cod, all the EAAs, barring lysine and all the NEAAs decreased significantly with development.     

Optimization of the supplemental essential amino acids to a fish meal-free diet based on fermented soybean meal for rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

To minimize the supplemental essential amino acids (EAAs) to a fish meal-free diet for rainbow trout Oncorhynchus mykiss, four types of fish meal-free diets and a control fish meal-based diet were fed to triplicate groups of trout (initial BW, 16 g) for 10 weeks. Two fish meal-free diets based on a fermented and an unfermented soybean meal were unsupplemented with EAAs (diet FSBM and SBM), and two fish meal-free diets based on the fermented soybean meal were supplemented with a combination of lysine and methionine (diet F + ML) and all EAAs (diet F + All), the EAA contents of which were lower than those of the control diet (diet FM). Although physiological conditions such as the biliary bile acid status and morphological features of fish fed diet FSBM were improved and similar to those of fish fed diet FM, the growth performance was not significantly different (P > 0.05) from fish fed diet SBM. The growth performances and whole body protein contents of fish fed F + ML and F + All diets were similarly improved compared to fish fed diet FSBM. These findings indicate that supplementation of lysine and methionine to a fermented soybean meal-based fish meal-free diet is enough to maximize the amino acid utilization of the diet.     

Effect of fish meal replacement with Carinata Brassica carinata in low animal protein diets of rainbow trout Oncorhynchus mykiss (Walbaum) on trypsin activity,protein and amino acid digestibility and bioavailability

Replacement of >25% of fish meal (FM) with aerobically converted carinata meal (ACCM) in low (200g/kg) animal protein (reference = 200g/kg FM) diets of rainbow trout Oncorhynchus mykiss resulted in reduced growth, partly due to reduced feed consumption and protein utilization. In this study, we determined the effect of FM replacement with ACCM on trypsin activity, apparent digestibility coefficients (ADCs) of protein, and essential amino acid (EAA) or conditionally essential amino acid (CEAA) ADCs and bioavailability. Replacement of FM did not alter protein ADCs or trypsin activity. Replacement of >25% FM reduced all EAA and CEAA ADCs except for arginine and leucine which were only reduced by 75% FM replacement. Only serum free lysine and muscle free histidine were reduced by >25% FM replacement. Muscle free lysine was only reduced by 75% FM replacement. Replacement of FM reduced EAA peak concentrations and resulted in slower release of EAAs in serum. Cumulative total EAAs in serum and muscle decreased with FM replacement. Ratios of EAAs to lysine showed that tryptophan was the most limiting EAA. However, isoleucine, leucine, methionine and phenylalanine were also inadequate for muscle synthesis for the first 9–12 hr following force‐feeding. Optimal time for protein synthesis was ≥36 hr. Although any level of FM replacement did not reduce protein ADCs and trypsin activity, replacement of ≥25% FM reduced EAA ADCs and bioavailability of lysine and histidine, which partly contributed to the observed differences in growth.     

达氏鲟仔鱼消化系统的发育及摄食初期食性的初步观察

本文描述了达氏鲟仔鱼消化系统的发育过程及仔鱼的食性．将仔鱼消化系统的发育过程归纳为三个阶段，即初期发育阶段、消化道分化完成阶段、发育完善阶段。这三个阶段与仔鱼的垂直游泳、水平游泳和进入底层生活三个生态阶段相对应．观察了仔鱼在池塘培育和室内饲养条件下摄食的种类、开始摄食时的长度及消化道内卵黄物质吸收的情况。根据仔鱼具有口腔齿及消化道结构的特点，认为仔鱼属底层肉食性鱼类的食性类型。其摄食对象主要是水蚯蚓和摇蚊幼虫等底栖无脊椎动物，其次是在池壁和水底活动的枝角类和桡足类。仔鱼的混合营养阶段不是发生在水平游泳阶段而是发生在进入底层生活之后，与其他的鲟科鱼类仔鱼不同。     

Use of supplemental amino acids on the success of reducing dietary protein levels for Jian carp (Cyprinus carpio var. Jian)

A feeding trial was conducted to investigate the effects of essential amino acids (EAA) supplementation on the success of dietary protein reduction for Jian carp (Cyprinus carpio var. Jian). Five diets were formulated including a positive control (Diet 1, 378.4 g/kg protein), a negative control (Diet 5, 289.8 g/kg protein) and three test diets (Diet 2‐Diet 4, 340.4–299.0 g/kg protein supplemented with EAA). No significant decline of growth performance in fish fed decreased dietary protein with EAA supplementation, which were significantly higher than the negative control. The apparent digestibility coefficients (ADC) of protein and most EAAs were not significantly affected by the dietary treatments. Dietary treatments did not affect whole‐body composition, but influenced protein and EAAs retentions. Total ammonia nitrogen (TAN) excretion decreased with the decreasing dietary protein, and the highest plasma ammonia content was observed in fish fed Diet 5. Plasma glucose concentration increased with the decreasing dietary protein reduction, while other plasma parameters were not affected by dietary treatments. These results indicated that low‐protein diets (299.0 g/kg) supplemented with EAA can maintain protein, EAA digestibility and retention in Jian carp, and also has benefit in the reduction of TAN excretion.     

Assessment of the ideal ratios of digestible essential amino acids for pacu,Piaractus mesopotamicus,juveniles by the amino acid deletion method

The present study aimed to determine the ideal ratios of digestible essential amino acids (EAAs) for pacu (Piaractus mesopotamicus) juveniles by the amino acid (AA) deletion method. A completely randomized design which consisted of 11 treatments and three replicates each was used. The treatments included a control diet (CD) containing 55% of nonpurified natural ingredients and 45% of purified synthetic amino acids and ingredients, and other ten isonitrogenous and isoenergetic EAA limiting diets (LDs), each being deficient in 44.4 ± 0.02% of the respective EAA. Pacu juveniles with initial average body weight of 6.22 ± 0.09 g were distributed among 33 fiber glass tanks. Fish were fed with semipurified and extruded diets for 113 days two times a day until apparent satiation. The ideal ratio of each dietary EAA was calculated on the basis of the relationship between body N retention and amount of EAA deleted from the respective EAA LD. Based on the AA deletion method, the ideal ratios of digestible EAAs for pacu juveniles, relative to lysine requirement of 100% were estimated as: methionine 14.6%, threonine 35.0%, tryptophan 6.6%, arginine 62.8%, histidine 13.6%, isoleucine 26.3%, leucine 43.7%, phenylalanine 27.2%, and valine 35.8%.     

Modelling the effects of dietary methionine level and form on postprandial plasma essential amino acid profiles in rainbow trout (Oncorhynchus mykiss)

Aquafeed formulation is susceptible to affect amino acid (AA) availability for metabolic functions. Statistical models were applied to quantify the effect of dietary methionine level (from 6.01 to 16.17 g kg^?1 dry matter) and form (free, coated or bound) on postprandial concentrations of plasma essential amino acid (EAA) in rainbow trout. Twelve diets were formulated with pea and soya protein concentrate or fish meal as the main protein ingredients and were supplemented or not with increasing amount of either crystalline or agar‐coated methionine. Fish were acclimatized to one of the 12 diets for 6 weeks before postprandial plasma sampling (six sampling points up to 36 h, seven fish each time), further analysed for EAA content. Using generalized additive models, we show that (i) dietary methionine level and form explained 74% postprandial methionine plasma variations and that (ii) the methionine dietary form and plasma concentrations significantly affected the plasma concentrations of the other EAAs. Finally, linear model revealed a positive relationship (R² > 0.9) between plasma concentrations of the three branched‐chain AAs under the present experimental conditions. The results obtained add new information on the dietary effects on EAAs in the plasma availability and the interactions between them.     

河鳗人工繁殖的初步研究

本文报道了自1973年以来河鳗人工繁殖研究的基本情况，包括亲鳗催熟、催产以及胚胎发育和培育等试验内容。试验结果表明，在人工催熟和水温逐渐升高的条件下，大部分亲鳗在4月上旬至5月中旬性腺成熟。从1974年至1978年总的产卵受精率为8．4％(其中流卵和产死卵者不计在内)。亲鳗自然产卵的时间一般在凌晨4时至6时20分之间，水温在18．5—24．5℃范围。产卵行为较特殊，产卵前发情时，雄鳗和雌鳗先后由池底阴暗处游至水表，沿池边环游追逐，最后在较小范围内急游产卵授精，产毕又回至池底。海水盐度在23—29．8‰范围，均能产卵受精，并孵出鳗苗。孵出后头两天的仔鳗悬于水表；第3天的仔鳗，卵黄囊大部分吸收，消化道全通，在肠内开始发现食物团，肠道内有强烈的纤毛运动，鱼体开始悬于水中，有极缓慢的下沉和上升；第4天眼球出现黑色素，晶体透明，上、下颌能启闭，有四对牙齿；第5天，肠道有蠕动波，出现肝脏原基，静止时侧卧水底；第14天，仔鳗在微流水中能不断游动，在静水中常处于水底。仔鳗养至第19天，存活434小时。     

Nutrient Compositions and Properties of Antarctic Krill (Euphausia superba) Muscle and Processing By-Products

ABSTRACT

This study investigated the morphometrics, proximate chemical compositions, pH, total amino acid (TAA), fatty acid profile, and minerals of the processing by-products of Antarctic krill (Euphausia superba). The nutrient compositions and properties of the by-products were revealed by being compared to those of Antarctic krill muscle and the economically important species of freshwater prawns (Macrobrachium nipponense) and penaeid shrimps (Metapenaeus ensis). The by-products are worthy of utilization because of the high ratio to the total weight (65.7%). The crude protein contents in the muscle and by-products of krill are 17.4 and 11.7%, respectively. The krill proteins have higher contents of essential amino acids (EAAs). The EAAs constitute 42 and 37% of the TAAs in muscle and by-products, respectively. The krill processing by-products contain high levels of total lipid (3.3%), and polyunsaturated fatty acids constitute 34% of fatty acids with high levels of eicosapentaenoic acid (EPA; 19.08%) and docosahexaenoic acid (DHA; 10.02%). Krill meat provides considerable iron, zinc, calcium, selenium, and copper. It is imperative to lower the fluoride level (70.1 mg/kg, wet basis) in krill muscle. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) reveals that myosin heavy chain (MHC) and actin are the major proteins in muscle, and their contents vary between species.