太平洋鳕(Gadus macrocephalus Tilesius)仔鱼发育过程

采用显微观察、拍照、测量的方法,对太平洋鳕(Gadus macrocephalus Tilesius)人工培育苗种各阶段仔鱼的发育(0–80 dph day post hatching)进行了研究。结果显示,在水温为2–12℃、盐度为28–32、p H为7.8–8.2、光照为800–1200 lx、微充气静水的培育条件下,太平洋鳕早期仔鱼发育主要特征为:0–5 dph仔鱼完全营内源性营养,1 dph仔鱼黑色素沉积较初孵仔鱼颜色加深,眼球出现彩虹色素,5 dph仔鱼消化道已打通(除肝脏外);6 dph仔鱼开口摄食,消化道内有小颗粒物质,营混合性营养;9 dph大部分仔鱼卵黄囊吸收完毕,消化道内充满褶皱臂尾轮虫(Brachionus plicatilis),进入外源性营养期,血细胞流动清晰可见;12 dph仔鱼头部黄色色素带明显;15 dph仔鱼黑色素和黄色素密集,鳔器官开始形成;17 dph仔鱼开始出现彩虹色素;20 dph仔鱼眼球发育完善,腹动脉可观察到明显的血流,鱼体尾部色素点开始出现;30–50 dph仔鱼各鳍条雏形发育;30 dph仔鱼尾鳍鳍条开始发育;40 dph仔鱼开始摄食卤虫(Artemia sp.),第1、2、3背鳍已出现雏形;50 dph仔鱼尾椎骨开始上翘,臀鳍、背鳍雏形已清晰可见;60–80 dph仔鱼色素细胞进一步发育,各鳍条逐步发育完善,胆囊清晰可见;60 dph仔鱼鳃部呈现红色;70 dph仔鱼腹部有银白色鳞片雏形出现;80 dph仔鱼鳃盖已基本发育完善,腹鳍出现。本研究对太平洋鳕仔稚鱼发育过程进行了描述,可为后续规模化人工繁育的开展提供基础数据。     

斑点鳟仔、稚、幼鱼的形态发育

以斑点鳟(Oncorhynchus mykiss)发眼卵为材料,进行了发眼卵的人工孵化及仔鱼的人工培育研究。对斑点鳟仔稚鱼的形态发育进行了系统观察,描述了各发育期的形态特征,并测定生长参数。斑点鳟早期生活史的分期如下:初孵仔鱼全长14.25±0.45 mm,体重85±5 mg,肛门未开口,营内源性营养,脊柱末端向上弯曲;10 dph开始上浮,投喂卤虫;12 dph开口摄食,开始营内外源混合性营养;14 dph鳍膜消失,各鳍独立;16dph开始投喂配合饵料;24 dph卵黄囊吸收完毕,营完全外源性营养;34 dph,体侧形成8～9个幼鲑斑;44 dph各鳍的鳍条发育健全;60 dph幼鱼外形为纺锤形,与成鱼相同。研究表明,斑点鳟早期生长发育过程中全长、肛门前长、水平眼径和头高的生长情况基本相同,0～16 dph生长速度较快,16～44 dph生长速度较慢,44 dph后生长速度再次变快。     

黑棘鲷早期色素细胞发育与体色变化

对黑棘鲷早期发育过程中体色和色素细胞的分布及形态变化进行了连续观察。结果表明,黑棘鲷幼体黑色素在原口关闭前期开始出现,黄色素在嗅囊期出现,彩虹色素出现较晚,孵化后6d(Day post hatching,dph)在眼球上端出现,而后密集于腹腔(28 dph)以及鳃盖骨附近(32 dph)。黑色素细胞在发育过程中,不仅数量增多,而且形状也由点状逐渐变成以树枝状和雪花状为主,为幼体黑色素的发育过程;28 dph幼体黑色素完全被成体黑色素替代,形态上再次变为小点状。黄色素几乎伴随着黑色素的分布,色素细胞几乎无形态变化,最终被黑色素覆盖而不明显。初孵仔鱼,尾端6～8体节躯干部具有黑色素丛,构成了该鱼的种属特征。在28 dph,体色发育进入到模式形成期,首先在躯干部形成相互间隔的3个色素带,至40 dph共7条色素带形成,完成体色的模式发育。     

唐鱼的胚后发育

根据唐鱼(Tanichthys albonubes)发育过程特征,胚后发育可以分为孵出期、胸鳍形成期、鳔一室期、卵黄消失期、尾鳍分化期、背鳍分化期、鳔二室期、背鳍形成期、臀鳍形成期、腹鳍形成期、稚鱼期、幼鱼期和成鱼期。在水温23.0~29.0℃条件下,初孵仔鱼体全长为(2.760±0.002)mm。孵出后3天,巡游模式建立,仔鱼开口摄食;5天仔鱼卵黄耗尽,完全依赖外源营养;9天尾鳍开始分化,12天尾脊索上弯;15~18天,背鳍褶突起明显,鳍条原基出现;18天第二鳔室出现,肌节开始向“W”过渡;臀鳍与背鳍分化;33天,20%的仔鱼可观察到腹鳍条;45天,57.1%仔鱼身体长出鳞片;50~55天,体全长(15.62±1.65)mm,腹膜闭合,身体透明特点消失,进入幼鱼期。77天,部分性成熟较早的个体开始进行繁殖。同时文中讨论了唐鱼胚后发育特点及其保护生物学     

绿鳍马面鲀外部器官的早期发育

本研究分别描述了绿鳍马面鲀人工繁育过程中11个器官的发育特征。口:2～3dph开口后持续生长,在24～28dph出现短时期停滞,建议此时保证小型饵料供给。眼:1dph色素出现,3dph脉络膜形成、瞳孔黑色,4dph巩膜形成,14dph眼眶出现,40dph与成鱼基本一致。第一背鳍棘:3dph原基出现,7～8dph鳍棘初成,10dph凸出体外,14dph基本形成,60dph与成鱼基本一致。腰带骨与腹鳍棘:5dph腰带骨出现,60dph腰带骨与成鱼一致,5～7dph腹鳍棘生长迅速,10dph逐渐萎缩,至30dph全部脱落。胸鳍:15dph胸鳍膜加厚,鳍条形成,30dph基本发育完善。背、臀鳍:14dph出现支鳍骨和鳍条,24dph鳍条基本发育完全,60dph与成鱼基本一致。尾鳍:0～14dph尾椎平直,16dph尾尖下方出现鳍条原基,16～24dph尾尖上曲,鳍条完善并分节,50dph尾鳍圆形。皮肤:8dph表皮加厚,头部首先出现致密表皮,40dph全身被鳞;120dph成为柔韧结实的革状表皮。内脏团:2dph卵黄囊吸收完毕,肛门形成,出现第一个肠袢;3dph油球消失,仔鱼摄食;8～12dph肝、肾和鳔的原基出现,16dph肾脏、肝脏和鳔形成,18dph脾脏形成。连续测定了总高、肛门前长、水平眼径和下颌侧长的生长并绘制了生长曲线。     

太平洋鳕(Gadus macrocephalus)亲鱼驯化培育与早期发育特征

采捕山东威海外海黄海海域的太平洋鳕(Gadus macrocephalus)亲鱼进行驯化和培育,在人工条件下成功驯化存活野生亲鱼49尾,经短期促熟培育后,通过人工授精方式获得了多批次受精卵.对胚胎和早期仔鱼发育过程进行了观察,详细描述了从受精卵到早期仔鱼各发育时期的形态特征.结果显示,太平洋鳕成熟卵子为沉性卵,圆球形,卵径为0.9-1.1 mm,无油球.胚胎发育分为5个时期,分别为卵裂期、囊胚期、原肠胚期、神经胚期和器官形成期.在水温为9-10℃、盐度为27-29的海水中孵化,受精卵历时312 h 30 min孵化出膜.初孵仔鱼全长为(3.85±0.12) mm,6日龄仔鱼开口,肛门与外界相通,进入混合营养期.8日龄仔鱼卵黄囊消耗殆尽,开始进入外源性营养阶段.仔鱼开口饵料为轮虫(Rotifer),12日龄开始摄食卤虫(Artemia saline)无节幼体.6日龄仔鱼鳔原基形成,16日龄鳔充气成为亮泡状.12日龄仔鱼形成肠道第1个生理弯曲,22日龄仔鱼第2个肠道生理弯曲形成.研究结果可为太平洋鳕亲鱼驯化培育和苗种培育提供基础资料.     

瓯江产唇的早期形态发育研究

试验结果表明,受精卵授精后120 h,仔鱼开始出膜,初孵仔鱼(体长5.6~6.8 mm,平均体长6.35 mm)鱼体透明,体表和卵黄囊均无黑色素分布,尾鳍透明光滑,具口凹和眼色素并形成胸鳍原基,至卵黄被完全吸收时胸鳍鳍条开始形成,至28日龄时仔鱼各鳍发育完全,肌节数38~42。根据卵黄囊存在的情况和脊索的弯曲程度将仔鱼划分为卵黄囊仔鱼、前弯曲期仔鱼、弯曲期仔鱼、后弯曲期仔鱼。仔鱼眼径与头长比呈递减趋势,进入后弯曲期,体长迅速增加(≥11.8 mm)。唇鱼骨仔鱼体背与体侧黑色素由背鳍下方向尾部扩散,继而由中部至头部扩散。胸鳍附近最早出现鳞片,然后向后侧覆盖,最后在腹部出现鳞片。     

瓯江产唇(鱼骨)的早期形态发育研究

试验结果表明,受精卵授精后120 h,仔鱼开始出膜,初孵仔鱼(体长5.6~6.8 mm,平均体长6.35 mm)鱼体透明,体表和卵黄囊均无黑色素分布,尾鳍透明光滑,具口凹和眼色素并形成胸鳍原基,至卵黄被完全吸收时胸鳍鳍条开始形成,至28日龄时仔鱼各鳍发育完全,肌节数38~42。根据卵黄囊存在的情况和脊索的弯曲程度将仔鱼划分为卵黄囊仔鱼、前弯曲期仔鱼、弯曲期仔鱼、后弯曲期仔鱼。仔鱼眼径与头长比呈递减趋势,进入后弯曲期,体长迅速增加(≥11.8 mm)。唇鱼骨仔鱼体背与体侧黑色素由背鳍下方向尾部扩散,继而由中部至头部扩散。胸鳍附近最早出现鳞片,然后向后侧覆盖,最后在腹部出现鳞片。     

拉氏仔稚鱼发育、饥饿不可逆点及适时下塘研究

为探明拉氏■仔稚鱼发育生物学特性及适宜下塘时间,对拉氏■进行了胚后仔稚鱼发育显微观察、仔鱼饥饿试验和仔鱼下塘试验。胚后仔稚鱼发育观察结果显示,水温16～18℃,拉氏■初孵仔鱼全长(4.69±0.37)mm,卵黄囊全长(3.12±0.10)mm,2日龄眼点变黑,5日龄消化道开始贯通,6日龄仔鱼鳔一室开始充气,7日龄脊索末端开始弯曲,仔鱼开口摄食,9日龄卵黄囊消失,12日龄鳔二室形成,21日龄仔鱼鳔二室充气,23日龄仔鱼背鳍、臀鳍开始形成,27日龄仔鱼腹鳍开始形成,至35日龄仔鱼各鳍发育完善。仔鱼饥饿不可逆点试验结果表明,16～18℃,拉氏■仔鱼开口第1天(7日龄)初次摄食率为36.36%,9日龄达最高初次摄食率85.71%,饥饿不可逆时间临界点为仔鱼14日龄,此时仔鱼摄食率为40.91%。仔鱼开口前全长(L)与日龄(t)符合von-Bertalanffy生长方程:L=8.0031[1-e⁽-0.3139(t+2.8093))]。拉氏■适宜下塘试验结果表明,水温14.5～20.1℃,池塘轮虫生物量8.30～18.58mg/L,拉氏■仔鱼最高成活下塘时间、体质量增长的适...     

太平洋鳕(Gadus macrocephalus)亲鱼驯化培育与早期发育特征

采捕山东威海外海黄海海域的太平洋鳕(Gadus macrocephalus)亲鱼进行驯化和培育,在人工条件下成功驯化存活野生亲鱼49尾,经短期促熟培育后,通过人工授精方式获得了多批次受精卵。对胚胎和早期仔鱼发育过程进行了观察,详细描述了从受精卵到早期仔鱼各发育时期的形态特征。结果显示,太平洋鳕成熟卵子为沉性卵,圆球形,卵径为0.9–1.1 mm,无油球。胚胎发育分为5个时期,分别为卵裂期、囊胚期、原肠胚期、神经胚期和器官形成期。在水温为9–10℃、盐度为27–29的海水中孵化,受精卵历时312 h 30 min孵化出膜。初孵仔鱼全长为(3.85?0.12)mm,6日龄仔鱼开口,肛门与外界相通,进入混合营养期。8日龄仔鱼卵黄囊消耗殆尽,开始进入外源性营养阶段。仔鱼开口饵料为轮虫(Rotifer),12日龄开始摄食卤虫(Artemia saline)无节幼体。6日龄仔鱼鳔原基形成,16日龄鳔充气成为亮泡状。12日龄仔鱼形成肠道第1个生理弯曲,22日龄仔鱼第2个肠道生理弯曲形成。研究结果可为太平洋鳕亲鱼驯化培育和苗种培育提供基础资料。     

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.