杭州湾湾口与日本有明海产花鲈稚鱼的比较研究

本文基于采自杭州湾湾口、日本有明海和四万十川沿岸碎波带的天然花鲈仔稚鱼,研究比较了三者的外部形态、脊椎骨数、背鳍和臀鳍支鳍骨数的差异。杭州湾湾口和有明海水域的花鲈样本,体侧黑色素较少;吻长、体高和体长比相对较小;脊椎骨数分别为35,35.25±0.25;背鳍支鳍骨的平均值分别为25.33,25,均比四万十川的样本脊椎骨数(36)和背鳍支鳍骨的平均值(26)为少,探明了杭州湾湾口和有明海的花鲈仔稚鱼在特征上存在着相似性,与四万十川的样本有显著的差异。根据中国产花鲈的形态特征,对中国花鲈的学名进行了探讨,认为中国花鲈的学名应该为Lateolabrax maculates(McClellan)。     

棘头梅童鱼仔稚鱼脊柱及附肢骨骼的早期发育

本研究基于 2014 年 6–7 月在杭州湾北部水域用大型仔稚鱼网(口径 1.3 m、网目 0.5 mm)进行表层拖网所采集的棘头梅童鱼(Collichthys luncidus)仔稚鱼样本, 采用软骨-硬骨双染色技术, 探讨了棘头梅童鱼仔稚鱼(体长范围为 3.3~12.7 mm)脊柱及附肢骨骼的早期发育和骨化特征。研究结果表明: 脊柱骨化之前不分节, 而是由前向后逐渐长出的多个骨环把脊柱分节, 硬骨化出现的顺序大体上为由前向后。髓弓在脊柱骨化之前完全形成, 相对于一些低等鱼类髓弓等的生成方向是从中间向头尾和从后向前进行, 棘头梅童鱼的髓弓由前向后生长, 属于相对高等鱼类的生长类型。胸鳍支鳍骨是最先发育的附肢骨骼, 为能够自由地游泳摄食和从内源性营养转变为外源性营养提供了保障。后颞骨的形状十分特殊, 具有四枚向不同方向突起的棘; 背鳍支鳍骨由体中部开始向前后生长, 尾鳍支鳍骨的骨化晚于其他附肢骨骼, 侧尾下骨与其相邻的两枚尾下骨的基部融合, 为其游泳提供了强劲的动力。该研究结果不仅可以为早期形态学分类提供骨骼发育学方面的科学依据, 对棘头梅童鱼人工繁殖过程中结合骨骼发育进行技术上的契合也具有重要的参考价值。     

黑龙江抚远江段红鳍原鲌Cultrichthys erythropterus的年龄与生长

2014年7~10月在黑龙江干流抚远江段采集红鳍原鲌Cultrichthys erythropterus样本249尾,研究抚远江段红鳍原鲌种群的年龄结构与生长特性。结果表明,黑龙江抚远江段红鳍原鲌种群的年龄组成为1~7龄,以4~5龄鱼为主,占总样本量的67.8%;红鳍鲌为异速生长型,其体长和体质量的关系为W=0.0038L~(3.403)(n=248,R2=0.99,P0.01),红鳍原鲌体长与体质量的生长符合Von Bertalanffy生长方程:Lt=46.317[1-e~(-0.174(t+0.235))],Wt=1 771.325[1-e~(-0.174(t+0.235))]3.403,其生长拐点为t=6.80龄,对应的体长和体质量分别为32.70cm和541.66g。建议捕捞规格提高到体长300mm或体质量500g以上,以可持续开发利用黑龙江抚远江段红鳍原鲌渔业资源。     

长鳍吻(鱼句)年龄和生长的研究

对443尾长鳍吻鮈标本作了年龄和生长研究。用鳞片鉴定年龄并退算鱼的生长.得出体长与鳞径、体长与体重的相关式及生长方程。体重生长拐点在2.2龄。限制捕捞3龄以下个体,有利于资源增殖.     

绿鳍马面鲀胚后早期发育各阶段形态特征的研究

本文研究了绿鳍马面鲀(Thamnaconus septentrionalis)胚后早期发育各阶段可观、可量和可数性状的变化。结果显示，在水温为(23.0±1.0) ℃条件下，1 d出现胸鳍；4 d卵黄囊消失，鳔基和第1背鳍鳍基清晰可见；7 d油球消失，出现腹鳍；8 d第1背鳍鳍基和腹鳍出膜；9 d披透明圆形小鳞；12 d鳔和腹两侧后匙骨清晰可见；14 d出现第2背鳍支鳍骨和臀鳍支鳍骨；16 d披锥形小鳞，上、下颌出现锥形齿；19 d分化出第2背鳍鳍条和臀鳍鳍条；20 d尾柄下侧长出尾鳍鳍条；24 d时，第2背鳍、臀鳍和尾鳍的鳍条形态发育完全；27 d鳔大量充气。可量性状变化的曲线方程 R2 值均>0.90，第1背鳍鳍高，4~30 d呈指数递增；视囊0~11 和11~20 d为线性递增，0~11 d递增程度<11~20 d，21~30 d为指数递增；口裂4~13和22~30 d为线性递增，13~22 d为线性递减；全长、体长、体高和矢耳石直径等拐点前为线性递增，拐点后为指数递增，拐点集中在19~23 d。初孵仔鱼共27对肌节，头部6对，躯体21对；仔鱼末期，第2背鳍支鳍骨数为31~36根，臀鳍支鳍骨数为33~35根；稚鱼末期，第2背鳍和臀鳍鳍条数与支鳍骨数相对应，胸鳍鳍条数为15~18根，尾鳍鳍条数为12根；早期幼鱼45 d时，鳍条分节明显，第2背鳍鳍条2节，臀鳍鳍条3节，尾鳍鳍条为7~10节，50 d躯体4~5条黑色条带。研究较详尽地描述了绿鳍马面鲀胚后早期发育各阶段的形态特征，丰富了绿鳍马面鲀胚后早期发育基础资料，可为其苗种繁育提供指导。     

大弹涂鱼皮肤黏液的抑菌活性和蛋白质组学

皮肤黏液是鱼类免疫防御的第一道防线。大弹涂鱼皮肤黏液对其免疫防御、渗透压维持以及适应水陆生活等方面具有重要意义。为深入了解大弹涂鱼皮肤黏液的蛋白质分子组成,对其皮肤黏液开展了抑菌活性分析和蛋白质组学分析。通过电刺激法收集大弹涂鱼皮肤黏液,采用打孔法比较了皮肤黏液和血清的抑菌活性差异;进一步利用鳗弧菌对大弹涂鱼进行诱导,采用生长曲线抑制法分析和比较了诱导前后皮肤黏液的抑菌活性差异。利用Shotgun质谱技术,结合大弹涂鱼皮肤转录组数据库,对大弹涂鱼皮肤黏液开展了蛋白质组学分析;进一步利用String软件对所鉴定的蛋白质开展了蛋白质相互作用预测。大弹涂鱼皮肤黏液具有广谱抑菌活性,鳗弧菌诱导后的大弹涂鱼皮肤黏液与诱导前相比,对部分革兰氏阴性菌的抑菌活性明显上升,但对其他菌株的抑菌活性差异不明显。从大弹涂鱼皮肤黏液中共鉴定各类蛋白质分子97种,基本分子组成与其他硬骨鱼类皮肤黏液蛋白相似,但也有少数蛋白如泛素蛋白、胸腺素蛋白等未在其他鱼类皮肤黏液中报道。此外,其他鱼类中所鉴定到的部分蛋白如热休克蛋白、抗菌肽等在大弹涂鱼皮肤黏液中未能鉴定到。大弹涂鱼皮肤黏液中已鉴定的蛋白多数具有与免疫功能相关的结构域,且存在一个以肌动蛋白为核心的相互作用网络。大弹涂鱼皮肤黏液具有明显的广谱抑菌活性,其蛋白质组成与其他鱼类皮肤黏液具有一定的相似性。本研究为深入了解大弹涂鱼皮肤黏液的分子多样性及功能机制奠定了基础。     

湖北牛山湖红鳍原鱼白的个体生殖力

研究了湖北牛山湖红鳍原鱼白个体生殖力的分布特征、变化规律及其与各体征指标的关系。结果表明,红鳍原鱼白个体绝对生殖力在0.5万~3.0万粒,个体绝对生殖力与体长、体重和成熟系数分别呈直线、直线和幂函数关系,体长相对生殖力与体长和成熟系数分别呈直线和幂函数关系,体重相对生殖力与体长、体重和成熟系数的相关性不显著。多元逐步回归分析表明,红鳍原鱼白个体生殖力与性腺重、体长和成熟系数3个体征指标密切相关。     

衡水湖红鳍原鲌的年龄、生长和繁殖特性研究

为研究衡水湖红鳍原鲌(Cultrichthys erythropterus)的年龄、生长和繁殖特性，在衡水湖采集261尾红鳍原鲌，测定其年龄、体长、体重、性腺发育时期、性腺重等。结果表明，衡水湖红鳍原鲌的2～3龄为优势龄组，从4月份开始，随着气温的逐渐回升，平均年龄呈现出缓慢上升的趋势，到6月份达到了最高，为1.95,之后从7月份开始又逐渐降低。红鳍原鲌的体长范围为76～238 mm,均值为119 mm;体重范围为5.5～113.1 g,均值为24.6 g。红鳍原鲌的雌性个体为正异速生长，雄性个体为负异速生长。红鳍原鲌的雌雄种群性比为0.903∶1,体长150 mm以下种群，雄性个体占据优势(雌雄比0.87∶1);体长150 mm以上的种群，雌性个体占据优势(雌雄比1.36∶1)。衡水湖红鳍原鲌的繁殖期为4—9月，主要集中在6—7月。卵径范围为0.30～1.20 mm,主要集中在0.60～1.00 mm,根据卵径的变化趋势推测其产卵类型为分批产卵。     

太湖河川沙塘鳢的生物学研究

研究了河川沙塘鳢的年轮特征、生长特性、繁殖和摄食习性。观察比较了耳石、鳞片、脊椎骨和胸鳍支鳍骨的年轮特征，选取耳石作为鉴定年龄的依据。渔获物有０～Ⅳ龄五个年龄组，其中Ⅰ和Ⅱ龄组占渔获量的８５％，Ⅳ龄组仅为１．０２％。体长与耳石半径呈直线相关。体长与体重（Ｗ）和纯体重（Ｗ′）均呈指数函数增长关系，Ｗ＝２．２４１６×１０－２Ｌ３．０８６７；Ｗ′＝２．４９８×１０－２Ｌ２．９７４７。卵巢发育分Ⅵ期及重复发育的Ⅳ′和Ⅴ′期，属分批非同步型产卵鱼类，产卵时间为３～６月，盛产期为４～５月，繁殖期间至少产两次卵。该鱼主要以无经济价值的小鱼和虾为食     

北部湾斑鳍白姑鱼的年龄与生长

通过对斑鳍白姑鱼(Pennahia pawak)鳞片年轮的观察和基础生物学测定,研究斑鳍白姑鱼的年龄判定与生长特性.采用自2008年8月至2009年5月北部湾海域底拖网、流刺网和钓具作业的斑鳍白姑鱼渔获样本,共计626尾.结果认为斑鳍白姑鱼鳞片的年轮显示为空白型窄带,边缘增长率MGI计算结果表明,年轮主要在9-11月形成,为1年1个周期;性腺成熟指数(GSI)表明,繁殖期为4-8月份,年轮形成于繁殖期之后.本研究利用最大似然法估算了von Bertalanffy、Logistic、Gompertz和Generalized von Bertalanffy生长方程的生长参数,ARSS检验得出雌雄生长在4个生长方程中均无显著性差异(P>0.05),AIC、AIC差值和BIC检验得出Logistic生长方程为最适生长模型,主要参数分别为:渐进体长L∞=220.32 mm,生长曲线的平均速率K=0.58,初始年龄t0=0.905.斑鳍白姑鱼在3龄之前生长迅速,之后生长趋于减缓.为保护产卵补充群体和合理开发利用北部湾的斑鳍白姑鱼资源,以及考虑实际渔业生产状况,建议以2龄的体长146.53 mm作为最小开捕体长标准.     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Protein and amino acid composition from the mantle of juvenile O ctopus vulgaris exposed to prolonged starvation

Protein and amino acid composition of the mantle of juvenile O ctopus vulgaris (Cuvier, 1797) during fasting for 27 days were determined. Average protein content of octopus mantle was of 711.19 ± 46.80 g kg^?1 DW, and it decreased with increasing fasting days. The non‐essential amino acids content was higher (486.18 ± 11.08 g kg^?1 protein) than essential amino acids (425.82 ± 9.15 g kg^?1 protein) at the start of the experiment (unstarved animals). The results suggest that the amino acid profile of the mantle where the most abundant amino acids are Arg, His, Lys, Gly, Leu and Pro could indicate a prolonged fasting condition (>20 days) or poor nutrition of O . vulgaris. This study supports the idea of using mantle for metabolic needs of starved O . vulgaris suggesting that the degradation pathway of amino acids to pyruvate and tricarboxylic acid cycle intermediates was favoured contrary to the degradation pathway of ketogenic amino acids. Special considerations should be taken concerning Thr, Ile, Ser, Ala, Asx (Asp, Asn), Glx (Glu, Gln) (because of their fast intake) and Lys and His (due to their stable contents) during a prolonged period of fasting.     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.     

Cardiac,ventilatory and metabolic responses of two ecologically dissimilar species of fish to waterborne cyanide

Changes in heart rate, ventilatory activity and oxygen consumption were determined in trout (Salmo gairdneri) and brown bullhead catfish (Ictalurus nebulosus) during exposure to a steadily increasing concentration of waterborne cyanide selected to produce death in 8–9 hours for each species. The lethal cyanide concentration for the bullheads was an order of magnitude higher than for trout. Trout developed an immediate and gradually increasing bradycardia throughout the exposure period. Cyanide produced tachycardia in the bullhead followed by a gradual onset of bradycardia as the concentration of cyanide was raised. Pericardial injection of atropine (a muscarinic cholinergic antagonist) indicated that bradycardia in the trout was due initially to increased vagal tone but later due to the direct effect of cyanide on the heart. Hyperventilation in the trout persisted throughout the exposure period, although the rate and amplitude fluctuated and was variable between individual fish. During the last hour of exposure (highest cyanide concentration), ventilation was characterized by rapid, shallow breaths followed by a sudden respiratory arrest. The bullheads exhibited hyperventilation during the first 3 hours of exposure followed by a gradual, linear drop in ventilation rate and amplitude until death occurred. Cardiac and ventilatory responses in both species were attributed to stimulation of central and peripheral chemoreceptors by cyanide. Evidence is presented which suggests the initial response in the bullheads was due, at least in part, to gustatory stimulation by the cyanide. Oxygen consumption of the trout remained above pre-exposure levels for the majority of the test period. Oxygen consumption in the bullhead paralleled the changes in heart and ventilatory rates. Whole-body lactate levels of fingerlings of both species during cyanide exposure were measured to estimate the extent of anaerobiosis. Whole-body lactate levels were much greater in the bullheads than the trout, indicating a higher capacity for anaerobiosis, possibly due to a greater fuel supply. Overall, the trout responded to cyanide in a manner similar to that produced by environmental hypoxia whereas the bullheads experienced a gustatory stimulus which masked the hypoxia-like response.     

An overview of stress physiology of fish transport: changes in water quality as a function of transport duration

This study brings an integrated analysis about the relationship between water deterioration and its physiological consequences in live fish transport. The analysis was focused on the transport water and its deterioration, and physiological challenges imposed on the fish. Usual commercial handling procedures employed to mitigate fish stress during transport were discussed. Future topics of research for the establishment of safer fish transport protocols were proposed. Transport was classified into short (≤8 h) or long transport (>8 h). The main issue in short transports should be the prevention of water pH reduction, while in long transports it is the increase in ammonia. Plasma cortisol is the most employed marker for stress and is acutely elevated upon short episodes of transport, but remains elevated even in long‐transport events. Plasma glucose is perhaps a better marker for handling stress. Plasma lactate, pH, osmolality CO₂ and ions should be more often evaluated. Plasma Na⁺ and Cl^‐ are very useful markers of acidosis, due to their respective exchange for H⁺ and , for acid–base regulation. The establishment of species‐specific transport protocols should be preceded by such combined analyses of water and physiological parameters.     

Are hatchery‐reared abalone naïve of predators? Comparing the behaviours of wild and hatchery‐reared northern abalone,Haliotis kamtschatkana (Jonas, 1845)

Abalone populations have declined worldwide, generating interest in enhancement using hatchery‐reared individuals. In many cases, such restoration efforts have met with limited success due to high predator‐induced mortality rates. Furthermore, the mortality rates of outplanted hatchery abalone are often considerably higher than for wild individuals. This study uses northern abalone (Haliotis kamtschatkana) as a case study to determine whether hatchery‐reared abalone behave differently than their wild counterparts. In the field, outplanted hatchery‐reared abalone were significantly less responsive than wild abalone, in terms of number of abalone responding and intensity of response, to nearby movement and to physical contact with an inert probe. Also, when encountering a cue to which all abalone responded (a seastar predator), hatchery‐reared individuals remained subdued. Anti‐predator behavioural deficits in hatchery‐reared abalone were more pronounced in 4‐year‐old individuals than in 1‐year‐old individuals, suggesting an influence of either age or amount of time spent in the hatchery environment. These behavioural differences are expected to increase the vulnerability of hatchery‐reared abalone to predators, and are likely a major cause of their elevated predator‐induced mortality when outplanted.     

Effects of cadmium on the kinetics of calcium uptake in developing tilapia larvae, Oreochromis mossambicus

The toxic effects of Cd²⁺ on Ca²⁺ influx kinetics in developing tilapia (Oreochromis mossambicus) larvae were evaluated. Addition of 20 µg l^-1 of Cd²⁺ to the environment of 0 and 3 day-old larvae competitively inhibited the Ca²⁺ uptake within 4h resulting in a great increase in K_m values for Ca²⁺ influx (19.3 and 17.4 fold, respectively) as compared with their respective controls. Consequently, the actual Ca²⁺ influx of larvae in solutions of 0.2 mM Ca²⁺ are suppressed by 32–45%. Also, 3 day-old larvae were more sensitive to internally accumulated Cd²⁺ than 0 day-old larvae. Although the Ca²⁺ influx in 0 and 3 day-old larvae may be restored to the levels of their respective controls with 24h of being transferred to a 20 µg l^-1 Cd²⁺ solution, total body Ca²⁺ content was significantly reduced in 3 day-old larvae. Increased Ca²⁺ uptake efficiency ensures sufficient Ca²⁺ for normal growth. However, rapid increase in Ca²⁺ influx after hatching also leads to higher Cd²⁺ uptake. Exposure to Cd²⁺ will lead to a drop in body Ca²⁺ content resulting in retardation of larval growth. Therefore, we conclude that if Ca²⁺ uptake is interfered with at this critical stage of development, larvae will not be able to maintain normal levels of body Ca²⁺ and will show signs of Cd²⁺ poisoning.     

Migratory dynamics of stream-spawning longnose gar (Lepisosteus osseus)

Abstract– Literature evidence suggests that lake-dwelling longnose gar (Lepisosteus osseus) enter tributary streams to spawn, Until the present study, the dynamics of this breeding migration had never been investigated quantitatively. During the summers of 1991 and 1992, longnose gar were captured as they entered Weaubleau Creek, Missouri, a tributary of Harry S. Truman Reservoir. The in-stream spawning migration began in early April and ended in late May, and was positively correlated with stream flow and water level, and negatively correlated with water temperature. In-stream residence times ranged from 15 to 94 days, with males exhibiting longer residence times than females. Once in-stream, longnose gar travelled as far as 10 km upstream and occupied certain pools at greater relative frequencies. Although the reason for this preferential utilization is not completely understood, it may relate to pool depth and riffle proximity. Longnose gar disperse from the spawning stream great distances, with gar captured in Weaubleau Creek being recaptured up to 48 km away. This information should provide fisheries biologists the means to consider the reproductive ecology of this species in their conservation and management decisions.     

Nutritional regulation of hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition in zebrafish (Danio rerio) and tilapia (Oreochromis niloticus)

The desaturation and elongation of [1-¹⁴C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level. This revised version was published online in August 2006 with corrections to the Cover Date.