放养密度对池塘循环水养殖翘嘴鳜生长的影响

为探索池塘循环水条件下不同养殖密度对翘嘴鳜(Siniperca chuatsi)生长的影响,按占池塘面积6%的比例建设养殖单元,剩余94%水体作为尾水净化单元,构建了翘嘴鳜和水生植物(藕、菱)的复合养殖系统。2018年6月,试验设置了20、30、40尾/m2三个养殖密度梯度,每个放养密度组重复3次,对不同养殖密度翘嘴鳜的生长速度、饵料系数、肌肉中营养物质含量进行了测定。结果显示:随着养殖密度的增加,翘嘴鳜平均日增重由4.86 g降至4.19 g,成活率由92.88%降至86.49%,饵料系数由3.77增至4.34。肌肉干物质中共检测出17种氨基酸,总氨基酸(TAA)含量是76.06~80.89 g/100 g、必需氨基酸(EAA)含量是30.39~31.28 g/100 g。肌肉中营养物质包括TAA、EAA、非必需氨基酸(NEAA)含量等均没有随着养殖密度的变化而发生规律性变化。结果表明,池塘循环水条件下适宜养殖密度为30尾/m2。     

养殖密度对地图鱼幼鱼生长发育的影响

在室内水族箱中养殖地图鱼的幼鱼,密度分别为50、100、200、400尾/m2,共养殖28d。试验结果表明,各密度组地图鱼幼鱼的生长速度存在明显差异,增重率、增长率、特定生长率和平均日增重都随养殖密度的增加而降低;高密度组(400、200尾/m2)地图鱼的幼鱼个体生长速度离散度明显加大。     

摄食不同饵料对翘嘴鳜生长、体成分和消化酶活性的影响

为探究三种不同饵料对翘嘴鳜(Siniperca chuatsi)生长性能、体成分和消化酶的影响,实验选取初始体重为(113.56±11.82)g的翘嘴鳜900尾,随机分成3组,分别投喂活饵料鱼、冰鲜饵料鱼和商品饲料,进行60 d的养殖试验。结果显示:(1)冰鲜组、活饵组和饲料组翘嘴鳜的成活率、增重率、特定生长率和蛋白效率均无显著性差异。饲料组翘嘴鳜肥满度显著小于其他两组,肝体比和脏体比均显著大于其他两组。(2)三组翘嘴鳜体成分中的水分、蛋白质、粗脂肪和粗灰分均没有显著性差异。(3)翘嘴鳜肌肉各种氨基酸含量和总氨基酸量在三组之间的差异均不显著。饲料组翘嘴鳜肌肉中不饱和脂肪酸中的棕榈油酸、油酸、亚油酸、花生烯酸、EPA、神经酸、DHA的含量及总饱和脂肪酸、总单不饱和脂肪酸、总多不饱和脂肪酸均显著高于其他两组。(4)肝脏脂肪酶、肠道淀粉酶的活性在三组翘嘴鳜之间均没有显著性差异。冰鲜组翘嘴鳜肝脏淀粉酶、肠道脂肪酶活性均显著高于其他两组。结果表明:翘嘴鳜经过驯化可以摄食配合饲料,且不影响其生长性能。翘嘴鳜摄食饲料后,其肌肉氨基酸没有发生显著性的变化,不饱和脂肪酸的含量显著升高。     

养殖密度对西伯利亚杂交鲟幼鱼生长、抗氧化酶活性和相关基因表达的影响

为了研究流水养殖系统中养殖密度对井冈山地区西伯利亚杂交鲟（西伯利亚鲟Acipenser baerii♀×施氏鲟Acipenser schrenckii♂）幼鱼生长性能的影响,本文以初始体重为7.89±0.45 g/尾西伯利亚杂交鲟幼鱼为研究对象,设置了低密度组（1.16 kg/m3）、中密度组（1.74 kg/m3）和高密度组（2.32 kg/m3）三个密度组进行为期90 d的养殖生产实验,通过比较分析不同密度组西伯利亚杂交鲟生长指标、体成分含量、抗氧化酶活性和相关基因表达水平发现,低密度组幼鱼终体重、增重率及特定生长率显著高于中密度组和高密度组（P＜0.05）,各密度组实验鱼的存活率无显著性差异;水分和灰分随着养殖密度的增加而增加,且存在显著性差异,粗脂肪和粗蛋白未出现明显的差异;肝脏超氧化物歧化酶（SOD）和谷胱甘肽硫转移酶（GSH-ST）的酶活力在实验末期低、中密度组显著高于高密度组（P＜0.05）,随着养殖密度的增加,幼鱼肝脏丙二醛（MDA）含量不断增加,过氧化氢酶(CAT)活力降低,MDA和CAT在实验期间未出现明显的差异;结果还发现,高密度组与生长相关的生长激素受体（GHR）、胰岛素样生长因子-1（IGF-1）、胰岛素样生长因子-2（IGF-2）基因表达水平显著降低（P＜0.05）;高密度组与应激相关的热休克蛋白70（HSP70）基因表达水平在45d出现差异（P＜0.05）,90 d后高密度组显著高于低密度组（P＜0.05）,低密度组热休克蛋白90（HSP90）基因表达水平在30d时显著低于中、高密度组（P＜0.05）,实验末期,3个密度组间均存在显著的差异（P＜0.05）。 研究结果表明,实验条件下,中、低密度条件下西伯利亚杂交鲟幼鱼表现出良好的生长性能,因此建议,井冈山地区西伯利亚杂交鲟幼鱼养殖密度控制在1.16 kg/m3-1.74 kg/m3之间。     

翘嘴鳜♀×斑鳜♂杂交子一代早期生长速度

对翘嘴鳜♀×斑鳜♂(Siniperca chuatsi♀×S.scherzeri♂)杂交子一代和翘嘴鳜在0.3月龄、2月龄、7月龄和11月龄时的体重、体长和体高进行测量,从变异系数、杂种优势率、相对/绝对生长率、体重与体长的幂函数曲线以及肥满度5方面,对杂交子一代和母本翘嘴鳜的生长速度和杂种优势进行对比分析。结果显示,7月龄时杂交子一代的体重(300.4 g±118.2 g)与翘嘴鳜(305.2 g±82.5 g)差异不显著,且在7月龄时体重、体长和体高的月相对生长率(280.13%,25.30%和27.55%)比翘嘴鳜显著增高(89.62%,15.90%和12.72%);在0.3月龄和11月龄时体长的超亲杂种优势率分别为2.48%和0.91%;11月龄时杂交子一代的体重(540.88 g±173.66 g)显著低于与翘嘴鳜(624.45 g±154.11g)(P0.05);杂交子一代和翘嘴鳜体重与体长关系幂函数生长方程的决定性指数R2(0.992和0.995)、条件因子a(0.059和0.058)和异速生长因子b(2.722和2.740)在数值上非常接近。结论认为,尽管在总体生长速度上翘嘴鳜♀×斑鳜♂杂交子一代较母本翘嘴鳜略慢,但其早期的生长趋势与翘嘴鳜相似,并在体重与体长的生长关系方面具有良好的一致性。杂交子一代遗传了母本翘嘴鳜的快速生长性能,并在体长性状上显现出一定的超亲杂种优势。本研究通过分析养殖翘嘴鳜♀×斑鳜♂杂交子一代的生长速度,探讨杂交子一代的早期生长趋势及其杂种优势,旨在为杂交子一代的规模化人工养殖和品种选育等提供参考数据。     

密度胁迫对黄姑鱼幼鱼生长、代谢及非特异性免疫的影响

随机选取体质量为10.0~10.7g的黄姑鱼Nibea albiflora幼鱼450尾，设置4个养殖密度，依次为15尾/缸（1.49 kg/m3）、30尾/缸（3.00 kg/m3）、45尾/缸（4.84 kg/m3）、60尾/缸（5.81 kg/m3），研究密度胁迫对黄姑鱼幼鱼生长性能、代谢酶活性及非特异性免疫的影响。结果表明: 1) 养殖密度对黄姑鱼幼鱼的增重率没有显著性影响（P＞0.05）。特定生长率具有与增重率相类似的变化规律。饵料系数与养殖密度呈显著的负相关性：FCR=0.02G+0.11(n=15，R2=0.983，F＜0.05）。2) G60组乳酸脱氢酶活性最高并显著高于G15组、G30组（P＜0.05）。随着养殖密度的增大，谷丙转氨酶活性有逐渐增大的趋势（P＞0.05）。谷草转氨酶活性具有与谷丙转氨酶相类似的变化规律。3) 随着养殖密度的增大，血清溶菌酶活性呈现逐渐降低的趋势，G60组血清溶菌酶活性最低并显著低于其他3组（P＜0.05）。密度胁迫对血清补体C3、C4含量的影响均不显著（P＞0.05）。本研究表明，养殖密度过高会对黄姑鱼幼鱼的代谢及非特异性免疫造成负面影响，而养殖密度过低又会造成水资源的浪费，30尾/缸（3.00kg/m3）为较适宜的养殖密度。     

网箱养鳜优化技术

网箱养鳜优化技术鳜鱼为肉食性凶猛鱼类，已作为名优水产养殖对象广受生产者与消费者青睐。天然水域鳜鱼种类包括翘嘴鳜、大眼鳜、长体鳜、斑鳜、暗鳜等，其中人工养殖与繁殖的主要为翘嘴鳜，即鳜（Ｓｉｎｉｐｅｒｅａｅｈｕａｔｓｉ）。近年发展起来的网箱养鳜技术，在我...     

养殖密度对华南鲤幼鱼生长特性的影响

为了提高稻田养殖的效率,了解不同养殖密度对华南鲤(Cyprinus carpio rubrofuscus)幼鱼生长特性的影响,本研究在室内水族箱中养殖初始体质量约为0. 35 g、孵化三周的华南鲤幼鱼,密度分别为M1 (43. 48尾/m2)、M2 (86. 96尾/m2)、M3 (173. 91尾/m2)、M4(347. 83尾/m2)四个组,进行11周的养殖试验。试验结果表明,养殖密度对存活率无显著影响,但华南鲤幼鱼的体质量、体长、日增重(DWG)、净增重(NY)、肥满系数、变异系数(CV)和特定生长率(SGR)都随着养殖密度的增加而降低; M1组的体质量、体长、日增重、净增重、特定生长率均最大,其中日增重、净增重、特定生长率均与M2组无显著差异,但是M1组的变异系数较M2组要小。研究结果表明,此阶段华南鲤幼鱼最适养殖密度为M1 (43. 48尾/m2)。     

反季节翘嘴鳜养殖技术

正翘嘴鳜又称季花鱼、桂花鱼等,在分类学上隶属于鲈形目,翘嘴鳜科,其不但肉质细嫩,味道鲜美,而且蛋白质含量高,营养丰富,是深受广大消费者青睐的淡水名贵经济鱼类。目前江苏省翘嘴鳜养殖的普遍方式是当年夏花直接养成商品鱼,即4月下旬到5月初从广东购进1.0~1.5 cm翘嘴鳜乌仔下塘标粗至5 cm左右的夏花,分塘进行成品养殖,放养1 000~1 500尾/667 m~2,同时从广东购买鲮鱼     

基于转录组测序对翘嘴鳜(Siniperca chuatsi) 2种肌球蛋白重链基因的克隆与分析

肌球蛋白重链(Myosin heavy chain,MYH)是骨骼肌粗肌丝的重要组成单位,其表达量高低影响肌纤维的组成和肌肉生长.为了解其在翘嘴鳜(Siniperca chuatsi)早期生长过程中的作用,本研究从前期生长差异显著的2组(快长组和慢长组)翘嘴鳜幼鱼转录组差异表达Unigene中筛选出2个MYH基因,RACE (Rapid amplification of cDNA ends)克隆到其全长cDNA(MYH-7a,MYH-7b).MYH-7a全长为6071bp,开放阅读框为5820 bp;MYH-7b全长为5896 bp,开放阅读框为5745 bp.序列分析显示,2个MYH均有Loopl、Loop2环、ATP结合位点等关键结构域;进化树聚类分析显示,MYH-7a与MYH-7b均属于慢肌球蛋白.实时荧光定量PCR验证发现,其在快长组样本中表达量显著高于慢长组,与转录组测序结果一致;检测其在翘嘴鳜心肌、红白肌和皮肤等14种组织的表达水平,结果显示,MYH-7a主要在心肌中表达,而MYH-7b主要在红肌中表达;在胚胎发育不同阶段,二者随着胚胎发育的进行,表达量不断增加;在幼鱼早期生长过程(孵化出膜后15 dph、30 dph和60 dph)的翘嘴鳜白肌中,在15 dph和30 dph快长组的表达量显著高于慢长组,而到60 dph时快长组的表达量均显著低于慢长组.翘嘴鳜MYH-7a、MYH-7b在快长组与慢长组鱼中的差异表达提示它们在翘嘴鳜胚胎及其早期生长发育过程中发挥重要作用.     

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.