江鳕胚后形态发育特征

在直径2m的圆形玻璃钢槽内,水深0.3m,弱光,水温6～16℃下,详细观察了江鳕（Lota lota Linnaeus）胚后发育过程。结果表明,依形态发育,将出膜后的江鳕发育分为两个阶段（仔鱼期和稚鱼期）11个发育期。仔鱼期分为卵黄囊期仔鱼和后期仔鱼,历时62d;卵黄囊期仔鱼由单独依靠内源营养至混合营养过程,包括孵出期、胸鳍形成期、鳃弧期、鳔形成期和腹鳍形成期,历时31d;后期仔鱼从卵黄囊和油球消失,仔鱼完全依靠外源营养到各鳍基本形成为止,包括卵黄消失期、尾鳍形成期、背鳍分化期和臀鳍形成期,历时31d。稚鱼期包括鳞片出现期和鳞片形成期,历时5d。卵黄囊期仔鱼生长发育缓慢,后期仔鱼期和稚鱼期生长发育较快。     

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。     

多纹钱蝶鱼胚胎发育及胚后发育观察

为建立多纹钱蝶鱼(Selenotoca multifasciata)人工繁育技术, 为其生产性育苗工艺和管理技术的建立提供科学依据, 采用人工养殖的多纹钱蝶鱼经人工催产获得受精卵, 对胚胎及胚后发育阶段进行了连续观察、拍照和测量。结果显示, 水温(27.0±1.0) ℃, 盐度 32 条件下, 多纹钱蝶鱼从受精卵发育, 经 18 h 20 min 出膜, 受精后 3 h 进入囊胚期, 4.5 h 进入原肠期, 8 h 进入胚体形成期, 8.5 h 进入器官形成期, 器官形成顺序为视囊期、尾泡形成期、肌节期、脑泡期、耳囊期、尾芽期、尾鳍期、晶体形成期、耳石形成期, 16.5 h 出现心跳, 17.5 h 出现肌肉效应, 18.5 h 完成出膜。多纹钱蝶鱼胚后发育分为仔鱼期、稚鱼期和幼鱼期, 初孵仔鱼全长 1.350~1.655 mm; 水温 26 ℃下, 出膜后 2 d 卵黄囊完全消失; 出膜后 3 d 仔鱼开口, 口裂 0.265~0.280 mm; 出膜后 15 d, 鱼体体色加深, 进入稚鱼期; 19 d, 胸鳍发育完全; 23 d, 背鳍发育完全; 29 d, 尾鳍、臀鳍发育完全; 33 d, 鱼身上鳞片基本长出, 身体不再透明, 发育至幼鱼期, 此时全长 15.625~15.647 mm, 体长 12.013~12.234 mm, 体重 0.045~0.059 g, 心跳 150~159 次/min。     

七带石斑鱼胚胎及仔稚鱼形态观察

对七带石斑鱼胚胎和仔稚鱼发育过程进行了观察,描述了从受精卵到仔稚鱼各发育时期的形态特征;在水温22±0.5℃、盐度30条件下进行七带石斑鱼仔鱼的饥饿耐受力实验,记录了饥饿条件下初孵仔鱼的存活与生长、卵黄囊与油球的利用情况。结果表明,胚胎发育可划分为卵裂期、囊胚期、原肠胚期、神经胚期和器官形成期。在水温20.5±0.5℃、盐度30.0条件下,受精卵历时38h45min孵化出膜。初孵仔鱼全长1.059±0.071mm,至4日龄全长2.27～2.36mm时,卵黄囊完全消失;16日龄,全长4.99mm时,鳔形成;至25～30日龄,尾鳍鳍条发育完整。在饥饿条件下,初孵仔鱼的死亡高峰出现在孵化后4～6d,半数死亡时间出现在5d,至7d饥饿仔鱼全部死亡。卵黄囊期仔鱼的生长可分为3个阶段:仔鱼初孵时的快速生长期,卵黄囊消失前后的慢速生长期,以及在不能建立外源性摄食后的负生长期。随着生长发育时间的延长,饥饿仔鱼与正常条件下仔鱼的生长差异显著(P<0.05)。饥饿仔鱼体长较短,头大且体瘦,长期饥饿后脑后部下陷。     

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...     

广东池塘培育条石鲷仔、稚、幼鱼的早期发育和生长

研究了在广东饶平池塘人工培育的条石鲷（ Oplegnathus fasciatus）仔、稚、幼鱼的形态发育和生长特性。条石鲷初孵的0日龄仔鱼全长（1.8755±0.060）mm,卵黄囊长径（0.739±0.135）mm,短径（0.489±0.089）mm。在水温为22~23℃的前期培育条件下,3日龄仔鱼的卵黄被完全吸收,而到第4天,仅见到卵黄囊残余物。混合营养期仅1 d。在水温为24~27℃、盐度29~30、pH 7.4~8.2条件下,3日龄的仔鱼已开口,但仍不能主动摄食,4日龄仔鱼便进入了外源性营养阶段。8日龄鳃弓形成,12日龄尾椎弯曲,25~30日龄仔鱼的背鳍、胸鳍、腹鳍、臀鳍、尾鳍先后出现,鳞片出现,进入稚鱼期。40日龄时进入幼鱼期,全身覆盖鳞片,条带全部形成,形态与成鱼相似。全长、体长、体质量和体高随日龄的生长速度均呈显著的指数函数关系,体高/全长之比在0~5日龄时急剧下降,随后逐渐增高,20日龄后趋于平缓。     

厚颌鲂胚后发育观察

以人工繁殖所得的仔鱼为材料,观察了厚颌鲂胚后发育过程,对各个发育期的形态特征进行了描述。结果表明,厚颌鲂胚后发育过程可划分为2个阶段16个时期。初孵仔鱼平均全长(4.78±1.12)mm,肌节数43对。孵出后115.5h卵黄吸尽,仔鱼完全依赖于外源性营养,进入晚期仔鱼阶段,此时仔鱼全长(7.11±0.90)mm。发育至47d时开始出现鳞片,标志着进入了幼鱼阶段,此时全长(19.75±3.71)mm。在22.2~25.0℃条件下经过68d的发育,全长(31.82±3.87)mm的鱼苗,鳞片出齐,基本具备成鱼特征。在胚后发育过程中,鱼体长度生长、鱼体长度性状间的比例关系并不相同,其中,孵出期的生长速度最大;肛后长/全长比例随胚后发育逐渐增加,最后稳定在45%左右;体长/体高比值逐渐减小,并逐渐与成鱼的比例接近。     

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。     

辽河水系洛氏仔、稚鱼形态发育与生长特征

本文研究辽河水系洛氏Phoxinus lagowskii lagowskii仔、稚鱼形态发育和早期生长。结果表明:在18.8~27.2℃下,洛氏初孵仔鱼全长为(4.46±0.43)mm,4日龄的仔鱼鳔一室,5日龄时开始摄食,6日龄卵黄囊完全吸收,13日龄时鳔二室,32日龄时各鳍发育完成;36日龄时开始出现鳞片;58日龄时除头部外全身被鳞,进入幼鱼期。根据卵黄囊、运动器官和鳞片的变化,洛氏早期发育可分为卵黄囊期(孵出0~5d)、后期仔鱼(6~35d)和稚鱼期(36~58d)。曲线拟合表明,卵黄囊体积(V)和全长(LT)与日龄(d)均呈二次多项式关系,相关方程分别为:V=0.0063d2-0.0870d+0.2863(R2=0.8167),LT=0.0083d2+0.2351d+4.8759(R2=0.9544);体质量(W)与日龄(d)呈指数函数关系:W=0.0006e0.1317d(R2=0.9719)。     

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、pH为7.8-8.2、光照为800-1200 Ix、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);6dph仔鱼开口摄食,消化道内有小颗粒物质,营混合性营养;9dph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;12dph仔鱼头部黄色色素带明显;15dph仔鱼黑色素和黄色素密集,鳔器官开始形成;17dph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;40dph仔鱼开始摄食卤虫(Artemia sp.),第1、2、3背鳍已出现雏形;50dph仔鱼尾椎骨开始上翘,臀鳍、背鳍雏形已清晰可见;60-80 dph仔鱼色素细胞迸一步发育,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;70dph仔鱼腹部有银白色鳞片雏形出现;80dph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.     

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.