Intercohort cannibalism and post-partum behaviour of juvenile swordtail Xiphophorus helleri Heckel (Pisces: Poeciliidae)

Newborn (i.e. neonate) swordtail Xiphophorus helleri Heckel attempted to escape cannibalization attempts in a downward direction more frequently than in any other direction. The downward escape response is likely to be anti‐predator behaviour. In addition, neonates were often able to escape cannibalization at the time of birth, despite no previous exposure to predators, which suggests that this anti‐predator behaviour is innate. However, neonates at the time of birth were more vulnerable to cannibalism than older juveniles, which supports the hypothesis that anti‐predator behaviour is, at least in part, further developed as a result of previous experience (i.e. learning).     

Biology and invasive potential of the introduced swordtail Xiphophorus hellerii Heckel (Poeciliidae) in Western Australia

• 1. The swordtail Xiphophorus hellerii is a popular ornamental freshwater fish that occurs as an introduced species in the aquatic habitats of at least 31 countries. Although introduced populations are found in other Australian states, the only known Western Australian population occurs in the Irwin River (29°15′S).
• 2. The biology of X. hellerii in the Irwin River in south‐western Australia is described from four seasonal samples, collected by seine net, between spring 2002 and winter 2003.
• 3. Pregnant females were collected in all seasonal samples, though juveniles were absent in spring, implying that juvenile mortality during late winter is high. Although mean length of pregnant females (38.7 mm) and mean gonadosomatic index (GSI) (14.7) were similar to reported data for X. hellerii populations in Queensland, mean fecundity was markedly lower in Western Australia, i.e. 34.1, cf. 60.15.
• 4. Logistic analysis of the percentage of female and male X. hellerii with developing and mature gonads predicted that the length at which 50% of the sexes mature was 30.8 and 31.5 mm SL, respectively. The sex ratios of females to males did not differ statistically from a ratio of 2:1.
• 5. The diet of all X. hellerii size classes was omnivorous (primarily vegetal matter/algae), although a significant difference was observed between the diet of juveniles and that of the two larger size classes (i.e. juveniles consumed greater quantities of aquatic invertebrates).
• 6. A melanic polymorphism (i.e. pigmented caudal peduncle and fin) was observed in approximately 5% of X. hellerii collected.
• 7. If released, the range of X. hellerii is likely to expand in anthropogenically modified habitats in tropical and temperate latitudes of Western Australia. Potential ecological impacts on indigenous fishes may be magnified owing to the depauperate nature of the endemic ichthyofauna including a lack of predators. Copyright © 2011 John Wiley & Sons, Ltd.

     

Effect of varying dietary lipid and protein levels on growth and reproductive performance of female swordtails Xiphophorus helleri (Poeciliidae)

We conducted a study to determine the effect of dietary protein and lipid levels on the growth and reproductive performance of a freshwater ornamental species, the swordtail (Xiphophorus helleri). Two protein levels (20% and 30%) with four lipid levels (8%, 12%, 16%, 20%) within each protein levels were tested through formulation of practical diets labelled as 20P8L, 20P12L, 20P16L, 20P20L, 30P8L, 30P12L, 30P16L and 30P20L respectively. Results showed that dietary protein level significantly influenced final weight, weight gain and specific growth rate, while dietary lipid did not influence any of these growth parameters. More specifically, increasing dietary lipid levels from 8% to 12–16% in both 20% and 30% protein levels significantly improved swordtail growth performance. Dietary protein levels positively influenced gonadosomatic and hepatosomatic indexes. Both dietary protein and lipid significantly influenced female muscle protein content. Significantly highest fry production was obtained from diets 30P12L and 30P16L, respectively, while diet 20P8L resulted in the lowest fry production. This present study indicates the dietary protein and lipid requirements for female swordtails for optimized growth and reproductive performances to be at 30% and 12% respectively.     

剑尾鱼卵黄蛋白原基因片段克隆、表达及蛋白检测方法的建立

本研究通过对剑尾鱼(Xiphophorus helleri)卵黄蛋白原基因片段的克隆和表达,建立了剑尾鱼卵黄蛋白原蛋白检测方法.根据已发表的底鳉(Fundulus heteroclitus)卵黄蛋白原mRNA序列设计引物,利用RT-PCR法扩增出1段1 118 bp的剑尾鱼卵黄蛋白原cDNA片段,序列分析表明该片段与其他鱼类卵黄蛋白原基因序列相似性较高,其中与底鳉和食蚊鱼(Gambusia affinis)的同源性分别达87.4%和96.7%.在对该片段所编码氨基酸序列可能抗原位点分析的基础上,进行PCR改造构建原核表达载体,预期得到258个氨基酸的表达蛋白.表达载体转入大肠杆菌DH5α,经热诱导后,SDS-PAGE分析有29 kD的表达蛋白产生,与预期相符.以重组蛋白免疫新西兰大白兔,获得抗血清.雌激素(β-雌二醇)对剑尾鱼诱导后,用重组蛋白抗血清作一抗,进行Westernblot分析.结果表明,该抗血清能与剑尾鱼卵黄蛋白原特异结合,可应用于剑尾鱼卵黄蛋白原的检测.卵黄蛋白原是环境雌激素研究中较为特异、灵敏的生物标志物,剑尾鱼卵黄蛋白原检测方法的建立,为剑尾鱼环境监测应用提供良好基础.     

7种观赏性剑尾鱼品种间杂交子代的体色及鳍形研究

7种观赏性剑尾鱼的自交、杂交,对其子代的体色(包括眼睛色彩)及鳍形等性状进行统计分析。试验结果表明,黑眼为显性基因控制,红眼为隐性基因控制,体色与眼睛颜色有一定的连锁关系;推测剑尾鱼体色遗传由数量性状基因参与控制;尾鳍燕尾相对于正常尾为显性,而且雄性尾鳍的燕尾和长臀鳍具有连锁性;高背鳍由显性基因控制,正常背鳍由隐性基因控制,拥有正常背鳍的个体,其基因型是隐性纯合,拥有高背鳍的个体,其基因型为杂合,初步推断显性纯合为致死基因型。     

剑尾鱼RW-H近交系20个微卫星位点的遗传结构

为了对水生实验动物剑尾鱼(Xiphophorus helleri)RW-H系近交15代的遗传结构进行研究,寻找该近交系的标志基因位点,选择20个在野生剑尾鱼群体具多态性的微卫星位点,对剑尾鱼RW-H系(红眼白体)30尾个体进行分析。结果表明,其中有17个位点为单态,有可能作为该近交系的标志基因位点;另外3个位点Msa012、Msa033和Msc036具有多态性,多态信息含量值分别为0.3047、0.3457和0.3648。通过Pop-gene 3.2软件分析得知全部基因位点的纯合率达到了95.83%,个体间平均遗传距离为0.0482(0.000 0~0.1625),遗传相似系数为0.9518(0.8500~1.0000),说明剑尾鱼RW-H系已经具有很高的近交程度。几个多态性位点的发现,可以指导近交选育,加快选育进度。本研究方法不仅检测出剑尾鱼RW-H系具较低的遗传多样性,而且可为中国建立分子水平的实验动物监测标准提供基础数据。     

Intra-cohort cannibalism among larval stages of perch (Perca fluviatilis)

Cohorts of perch larvae, hatched within 24 h, developed into a bimodal body size distribution as early as 6 days after commencement of external food uptake. At this development stage, intra-cohort cannibalism occurred among larval perch individuals of larval stage V (body size: 10.5±0.26 mm, 95% c. l.) on smaller siblings. In experimental trials the consumption rate (C: no. of prey/predator·hour) increased exponentially with size of predatory perch (L: mm) and at 21°C was expressed by the relationship log C=3.406·log L-3.848 (n=10, r²=0.98, P<0.001). For predatory perch in larval stage V, consumption rate was reduced when Daphnia pulex were added, while not in later stages. Perch larvae experimentally forced to live as true piscivores without additional food items developed from stage V to stage IX (15.8±1.34 mm) within the same time as those fed on Daphnia alone, but with increased mortality.     

A comparison of growth, survival rate, and number of marketable fish produced of swordtails, Xiphophorus helleri Heckel (Family Poeciliidae), between two types of culture systems

To test the effect of stocking density on growth, survival rates and size distribution of juvenile swordtails, Xiphophorus helleri Heckel, under different environmental conditions, fish were stocked at rates of 1, 3 and 6 fish I^?1. Growth was monitored over a 14-week period. Fish were weighed in six groups of 20 fish per tank. Size variation was determined at the end of the growth period by measuring the total length of each fish to the nearest mm. Fish were stocked in two different systems at three stocking densities (1, 3, and 6 fish I^?1) in replicate. The systems were an indoor aquarium system and a tunnel system under semicommercial conditions. In each system, increasing stocking rates resulted in a significant reduction of growth rates. In the aquarium system, survival rate was not related to stocking density, whereas in the tunnel system, fish at the highest stocking density had a lower survival rate than those kept at the two lower stocking densities. The number of marketable fish above a set size limit of 40 mm total length was not higher in fish stocked at 6 fish I^?1 than at 3 fish I^?1 at the end of the study. Therefore, a stocking rate of 3 fish I^?1 would be optimal. At the end of the study, fish were categorized into males, females and immature fish. Fish with a clearly visible gonopodium were classified as males, those with typical female characteristics as females, and small fish that were not yet differentiated as immature fish. The ratio of females to males was highly skewed in both systems, favouring a higher percentage of females. As stocking density increased, the female:male ratio was significantly reduced, which would result in a greater number of saleable pairs at increased stocking density. The implications of these results for the management of intensive production of swordtails are discussed.     

The Influence of Livefeed Supplementation on Growth and Reproductive Performance of Swordtail (Xiphophorus helleri Heckel 1848) Broodstock

The influence of supplementation of drum-dried flake feed with various levels of Daphnia sp. on the growth and fecundity of broodstock Xiphophorus helleri was evaluated. Weekly supplementation showed no measurable advantage over flake feed only. A direct correlation was demonstrated between fecundity and size of female fish when fed a formulated flake feed only. Fish fed a daily Daphnia supplement had a mean final weight of 5.97 g, feed conversion ratio of 1.33 and mean fecundity of 190 embryos per female, which was significantly higher than the yield from the non-supplemented or weekly supplemented treatments. Despite these differences, the number of young harvested during the experiment did not differ (P > 0.05) between treatments and this discrepancy was ascribed to parental cannibalism of new born juveniles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Bioenergetics of cannibalism in juvenile barramundi Lates calcarifer (Bloch): exploring growth advantage of fish fed live prey and formulated diet

The present study investigated the growth performance of juvenile barramundi Lates calcarifer (Bloch) fed conspecific prey (CP), formulated diet (FD) and a mix of both (MIX) using a bioenergetics approach. Fish in the MIX treatment ingested significantly more CP than FD by dry mass. However, prey mass ingestion and cannibalism rate in the MIX treatment were significantly lower than in the CP treatment. This indicates that the provision of alternative food does not complete mitigate cannibalism, but it can significantly reduce cannibalism in barramundi. Fish in the FD treatment showed a significantly higher daily food intake than fish in the CP or MIX treatments. However, fish fed conspecifics showed significantly better feed conversion efficiencies, apparent digestibility rates and growth performances. Exclusive cannibalistic barramundi assimilated significantly more energy consumed, with 1.5% of energy lost in faeces comparing with 7.3% of siblings feeding exclusively on FD. Consequently, exclusive cannibals channelized more energy consumption into growth (57.1%) than those fed solely on FD (43.9%). Therefore, high energy allocation into growth promoted better feed conversion efficiency and growth performance of cannibalistic barramundi than siblings fed solely on FDs. This study implies that fast‐growing cannibals may continuously prey on slow‐growing conspecifics due to growth advantage through cannibalism. Therefore, size heterogeneity should be reduced at initial stocking and controlled as fish grow to avoid the emergence of new cannibals.     

Effects of feeding conditions and size differences on aggressive behaviour and cannibalism in the Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel) larvae

We examined the effects of feeding conditions and size differences on the aggressive behaviour and cannibalism in Pacific bluefin tuna (PBT) Thunnus orientalis larvae. In a 24 h experiment, restricted feeding alone was found to remarkably increase the frequency of aggressive behaviour, which was further elevated by differences in fish size. In a 4‐day rearing experiment, while aggressive behaviour was increased by restricted feeding alone, the frequency of cannibalism did not change significantly. Although the frequency of aggressive behaviour did not increase with difference in size factor, small fish in this group gradually tended to die over 4‐day period. In the restricted feeding and size difference group, large fish were observed to bite the small fish, and almost all the small fish died on the day after the start of the experiment. These results suggest that the aggressive behaviour of PBT larvae is chiefly increased by the shortage of live food; however, deaths related to cannibalism mainly occurred in small larvae and rapidly increased with food restriction and differences in fish size.     

剑尾鱼卵黄蛋白原C(Vg C)全长cDNA的克隆及表达

利用逆转录聚合酶链式反应(RT-PCR)和cDNA末端快速扩增(RACE)等方法,克隆获得剑尾鱼卵黄蛋白原C(Vg C)基因的全长cDNA序列。剑尾鱼Vg C基因cDNA序列全长4 011 bp,其5′非编码区包含12 bp和3′非编码区包含246 bp;含有一个3 753 bp的开放阅读框(ORF),编码1 250个氨基酸,推测其编码氨基酸分子量大小为141.7 ku,编码氨基酸序列与其他鱼类卵黄白原C编码氨基酸序列相似性在44%～85%。荧光定量PCR结果显示,Vg C在剑尾鱼肝脏中表达量最高,脾、肾、卵巢中有微量表达,脑、肌肉、鳃中几乎没有检测到表达;对不同时间暴露在雌激素中剑尾鱼肝脏进行实时荧光定量PCR表达分析的结果表明,Vg C在剑尾鱼肝脏中第5天表达量最高,随后降低,第9天后维持相对较低的表达量。研究首次克隆了剑尾鱼Vg C基因全长cDNA序列,并对Vg C在剑尾鱼体内表达组织器官分布及雌激素诱导后不同时间表达谱进行了初步研究,为剑尾鱼生殖生理及环境污染物监测应用等不同领域研究打下重要基础。     

Influence of Varying Dietary Protein Content at Three Lipid Concentrations on Growth Characteristics of Juvenile Swordtails (Xiphophorus helleri Heckel 1848)

Three protein levels (30%, 38% and 45%) at three different dietary lipid concentrations (6%, 8% and 12%) were used to formulate nine different diets that were fed for 60 days to 6–8 weeks old juvenile swordtails (Xiphophorus helleri). It would appear that a diet of at least 45% protein at a 6% lipid concentration is needed for the best specific growth rate (1.27% per day) and feed conversion ratio (2.50) at this specific growth phase in X. helleri. No ‘protein sparing effect’ was found when lipid concentration was increased at lower protein levels. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature preference and acclimation in Poecilia sphenops (Pisces, Poeciliidae)

The preferred temperature (PT) of Poecilia sphenops (Pisces, Poeciliidae) (n = 240; 1.13 ± 0.06 g wet weight; 3.26 ± 0.88 cm standard length) from Presa Piedra Azul, Oaxaca, Mexico, was measured at acclimation temperature of 20 °C, 23 °C, 26 °C, 29 °C, 32 °C and 35 °C. The thermal preference of males was 25.5 °C in summer and 29.6 °C in winter; whereas females preferred 29 °C in both seasons. Fish held at 20 °C and 23 °C preferred temperatures 36% higher than their acclimation temperature (AT), and those held at 35 °C and 32 °C preferred 30% and 20% lower temperatures than their AT. In intermediate temperatures, no significant differences between PT and AT were found. The interval of thermal selection based on the higher (HAT) and lower (LAT) avoidance temperatures was of 10–14 °C and not different between sexes in both seasons. Knowledge of the thermal biology of P. sphenops based on the preferred and avoidance temperatures was very important in order to understand the capacity of the species to adapt to the thermal changes occurring in its habitat. Based on the results, we can recommend the use of P. sphenops in aquaculture owing to its thermal plasticity.     

剑尾鱼脑细胞系的建立及细胞色素P4501A的诱导表达

为了构建剑尾鱼脑细胞系并探讨其细胞色素P4501 a(CYP1A)基因的诱导效应,实验通过胰蛋白酶消化法对剑尾鱼脑组织进行体外培养,经连续继代培养,建立了可稳定传代的脑细胞系,命名为SFB.SFB最适培养液为含有15％胎牛血清(FBS)的DMEM/F-12和L-15等比混合培养液,培养条件为27℃,5％ CO2.生长特性研究表明,第65代细胞的群体倍增时间为43.048h,显示出旺盛的生长和分裂能力.染色体分析发现,培养细胞的染色体众数为48条,SFB核型公式为2n =2st +46t,臂指数(NF) =48,与剑尾鱼一致.诱导实验表明,SFB在10-8～ 10-5 mol/L的苯并(a)芘诱导下,CYP1A mRNA表达量显著提升,且表现出良好的剂量效应关系.脑细胞系的建立为剑尾鱼的毒理学评价研究提供了便利,也为其系统的生态毒理学应用打下基础.     

Environmental factors and sexual differentiation in Poecilia sphenops Valenciennes (Pisces: Poeciliidae)

Because environmental factors play an important role in the sexual proportions in fish and given that the studies that evaluate the interactions of such factors are scarce, the purpose of this work was to determine the combined effect of pH/temperature (23, 26 and 29 °C; pH 6, 7 and 8) on sex determination of Poecilia sphenops Valenciennes. The trial started with newborn organisms (n = 180) that were maintained in aquaria for 6 months until they could be separated by sex. Afterwards, nine groups of four females (0.81–1.48 g) and two males (0.36–0.63 g) were distributed in 20‐L aquaria until fertilization, gestation and offspring birth took part. The offspring were grown under the same conditions until they reached sexual maturity. The results indicated the strong interaction of the factors (P < 0.05) with a lower male/female ratio at pH 7 both at 23 °C (M/F = 0.12) as well as at 30 °C (M/F = 0.10) and higher ratios at pH 8 at similar temperatures (M/F = 0.7) to 23 °C and (M/F = 0.6) to 26 °C. The females dominated in all the combinations; the least favourable combinations were 23 and 26 °C at pH 8 with 0.7 and 0.6 M/F ratios respectively. The results obtained in the laboratory explain very closely the behaviour of the population of P. sphenops from Oaxaca in the natural environment that can be used in aquaculture for baitfish production and also for aquaculture purposes.     

再次分级、驯食对小规格鳡生长、残食的影响

研究了再次分级、驯食对初次分级产生的鳡(Elopichthys bambusa)幼鱼弱小群体(S群)生长、存活的影响.试验设5组,A组试验鱼取自初次分级并驯食后的大规格群(B群),为对照组;B、C、D、E组取自S群,B组再次分级不再驯食,所分两级为B1、B2亚组;C组再次分级再次驯食,两级为C1、C2亚组;D组不再分级再次驯食;E组不再分级不再驯食.饲养85 d.结果显示:A组全长(TL)、体重(BW)始终最高,终末BW以E组最低;E组体重特定生长率(SGRBW) (55～ 139 DAH)最低;总存活率(SR) (55 ～ 139 DAH)A组最高,C组其次,E组最低;总残食率(CR) (55～ 139 DAH)E组最高,D组其次;初始体重变异系数(CVBW)对总CR影响显著(P=0.001),可用线性模型y=0.514 9x -7.761 7(r2 =0.667)阐释两者关系.结果表明,再次分级和再次驯食有利于S群存活,但不能使S群规格在85 d内追及B群.     

Larval cannibalism rates in the mangrove crab Ucides cordatus (Decapoda: Ocypodidae) under laboratory conditions

Predation of zoeas by megalopae of Ucides cordatus is frequently observed in the laboratory during larval rearing, a phenomenon that could considerably reduce the output of larviculture. Experiments were carried out in the present study to assess how the survivorship of larvae at the end of the larviculture is influenced by cannibalism by megalopae on the larvae of earlier stages, as well as on other megalopae. In addition, tests were performed to assess whether the adoption of different feeding protocols can decrease cannibalism rates. Experiments were carried out in plastic vials containing ocean water (salinity 25 g L^?1) under controlled environmental conditions (26 °C and 16:8 h LD photoperiod). An ensemble analysis of all the developmental stages indicated that zoeal mortality rates were significantly higher in the presence of megalopae, a result that is consistent with cannibalism by megalopae. However, separate analysis for each developmental stage indicated that only zoea IV, V and VI show reduced survivorship. No cannibalism was detected among megalopae. Food supplementation using Artemia sp. at a density of 6 nauplii mL^?1 proved to be successful in reducing cannibalism rates, whereas supplementation at a lower density (0.3 nauplii mL^?1) failed to show such an effect. The implications of these results for the larviculture of U. cordatus are discussed.