刺参受精及早期胚胎发育过程的细胞学观察

采用HOECHST 33258染色荧光显微方法,对刺参成熟未受精卵以及受精过程中精子入卵、极体排放、雌雄原核的形成与结合、早期卵裂以及多精入卵等细胞学进行了研究。结果显示,刚产出的刺参成熟未受精卵呈圆形,核相处于第一次成熟分裂中期;在水温22~23 ℃、盐度29条件下进行受精,受精后12 min,完成第一次成熟分裂,释放第一极体;受精后20 min,大部分受精卵完成第二次成熟分裂,放出第二极体。受精后35 min,雌、雄原核开始在卵中央发生染色体联合;受精后80 min,部分受精卵完成第一次卵裂,受精后100 min,部分受精卵完成第二次卵裂。刺参在受精过程中存在极少数的多精入卵现象。     

单环刺螠受精过程的细胞学观察

利用组织学和荧光显微镜对单环刺螠(Urechis unicinctus)受精过程中精子入卵以及核相变化进行了观察.结果表明:单环刺螠成熟卵呈卵圆形,核相处于生发泡尚未破裂的第1次成熟分裂前期.在(21±1)℃时,精卵混合后约5 min,精子由卵偏向植物极一侧入卵,受精膜开举起,继而精核发生第1次膨胀.直至受精后约25 min,受精膜完全举起；受精后10～50 min,卵核相继完成二次成熟分裂,分别形成第一极体和第二极体；受精后50～70 min,精核卵核分别膨胀,形成雄原核和雌原核,进而相向迁移,最后在卵的中央联合形成合子核.受精后70～90 min,受精卵完成第1次卵裂,形成2个大小相等的卵裂球.单环刺螠受精全过程历时约70 min,略长于多数海洋无脊椎动物的受精持续时间.本研究旨在为今后单环刺螠人工育苗和新品种的培育提供基础资料.     

缢蛏受精和早期卵裂过程的细胞学变化观察

采用普通光镜、荧光显微镜和石蜡切片技术,对缢蛏受精和早期卵裂过程中的精子入卵、减数分裂、雌雄原核形成与结合、早期卵裂以及多精入卵等细胞学事件进行了显微观察。结果表明,缢蛏成熟未受精卵多呈圆球形或卵圆形,少数呈梨形,卵径为82～88μm,核相处于第一次成熟分裂中期;精子为典型的原生型,全长55～58μm,头部呈保龄球形,顶体前端的顶体杆呈特别细长的花丝状;在水温21～22℃、盐度10的条件下进行人工授精,精、卵混合后,精子迅速附着于卵子表面,启动卵子发育;受精后4～6 min,精子的头部已进入卵内并明显膨胀,卵子外形变圆,卵外附着的精子量明显减少;在受精后12～15 min、20～25 min,受精卵先后排出第一极体、第二极体,完成两次成熟分裂;第二次成熟分裂结束以后,精、卵核体积迅速膨胀,雄原核的膨胀早于雌原核,核膜重建,在受精后约30 min形成雌、雄原核;雌、雄原核均向卵子中央移动,雄原核旁边的精子星光清晰可见,随后二者在卵子中央以染色体联合的方式结合,联合核的染色体共同排列在纺锤体的赤道板上,形成第一次有丝分裂的中期分裂相;受精后40 min左右,受精卵进行第一次卵裂,染色体在纺锤丝的牵引下向两极移动,结果形成2个大小不等的卵裂球;受精后45～50 min,卵子进行第二次卵裂,核相变化与第一次卵裂相同,在与第一次卵裂垂直的纵轴方向上发生不等全裂,最终形成3小1大4个卵裂球;受精后60～70 min,胚胎进行第三次卵裂,仍为不等全裂,但自此次卵裂起已开始进行螺旋分裂。此外,对实验中发现的缢蛏极少量多精入卵、多极分离等异常细胞学现象进行了分析,并探讨了海洋贝类卵子阻止多精入卵发生的机制。     

菲律宾蛤仔受精及早期胚胎发育过程的细胞学观察

利用HOECHST 33258荧光染料对已固定的菲律宾蛤仔受精卵及早期胚胎样品进行染色的方法,连续观察记录了菲律宾蛤仔受精及早期胚胎发育的细胞生物学过程。结果表明,菲律宾蛤仔的成熟未受精卵子处于第一次成熟分裂中期;精卵混合后精子迅速结合于卵子周围并开始进行顶体反应;精子人卵后去致密并且激发卵子恢复两次成熟分裂,排放出第一及第二极体,完成成熟分裂;受精卵完全排放出第二极体的同时早期的精卵原核形成,随后二者相互靠拢,体积扩散膨大,在细胞中央位置形成各自的染色体组后完成联合;菲律宾蛤仔早期胚胎发育速度进程较快;在受精过程中存在极少数的多精受精现象。     

中国对虾受精过程的细胞学研究

通过光镜和电镜切片技术，对中国对虾的受挤过程进行了观察。结果表明，中国对虾成熟卵子处于第1次成熟分裂前期，卵子激活后产生胶质层，精子在卵子的诱导下产生顶体反应后进入卵子。中国对虾为多精入卵、单精受精。精子入卵后，卵子完成成熟分裂并举起围卵膜，但精子的存在并非此过程所必需。在卵子进行第1次成熟分裂时，其纺锤体旋转90°。卵子完成成熟分裂后，精卵原核原核化并向卵子中央移动，最后，精卵原核结合形成合子核，卵子完成受挤过程。     

兴国红鲤同草鱼杂交的受精细胞学研究

兴国红鲤与草鱼杂交虽属亚科间的远缘杂交,却符合鲤科鱼类一般的受精规律,精子由唯一的受精孔道进入卵内,单精入卵。受精的适当时间是在卵细胞第二次成熟分裂的中期。受精后7分钟形成精子星光。接着雄性原核、雌性原核先后形成,并逐渐靠拢;受精后40分钟两性原核结合(水温21℃);受精后45—50分钟出现新个体的第一次卵裂。说明草鱼精子对兴国红鲤成熟卵细胞不仅起激动作用,而且参与了遗传物质的组成。此系亚科间远缘杂交具有生活力的生物学基础。实验发现:在特定的条件下,同一批受精卵中,多倍体,单倍体,雌发育可能同时存在。本文还比较分析了常见的几种鲤科鱼类及其杂种受精的过程。     

泥蚶受精过程的细胞学荧光显微观察

采用荧光染色剂ＤＡＰＩ已固定的泥蚶成熟卵和受精卵进色染色的方法，在显微镜下观察泥蚶受精细胞学过程。通过ＤＡＰＩ的染色，在荧光显微镜下可清楚观察到，泥蚶的成熟未受精卵处于第一次成熟分裂的中期，精子入卵后分裂再次启动，释放出第一和第二极体，完成成熟分裂，部分受精卵的第一极体有极明显的分裂现象，精子入卵的部位是随机的，且自精子入卵至成熟分裂完成，入卵的精子在形态等方面将发生一系列变化，形成雄性原核。雌雄     

近江牡蛎受精过程、胚胎及早期幼虫发育特征

为了解近江牡蛎(Crassostrea ariakensis)从受精到早期幼虫发育阶段的发育特性，在水温22～24℃、盐度20～22的实验室环境中对采自山东东营丁字湾海域的近江牡蛎进行人工授精，利用普通光学显微镜和荧光显微镜对近江牡蛎受精、早期胚胎和幼虫发育过程中的形态和核行为变化进行观察，并对这一过程中牡蛎的壳长变化进行了统计分析。结果表明，近江牡蛎成熟的未受精卵呈梨形，卵径为50μm左右，核相处于第一次成熟分裂中期。受精卵在受精后15～20 min、25～30 min,先后排出第一、第二极体，完成第一次和第二次成熟分裂，在受精后30 min左右先后形成雄原核和雌原核；雌、雄原核各自形成染色体组，在卵子中央发生联合，染色体排列于赤道板上，形成第一次有丝分裂的中期分裂相；受精后45 min左右，受精卵进行第一次卵裂，形成2个体积不等的卵裂球；受精75 min后，受精卵开始第二次卵裂，90 min后形成4个卵裂球，进入4细胞时期；6 h后受精卵发育至桑葚期，8～10 h进入囊胚期，12～15 h后发育至担轮幼虫，27～30 h左右发育成D形幼虫，5 d左右进入壳顶幼虫时期，17 d后幼虫...     

斧文蛤精子超微结构与受精过程的细胞学变化

采用电镜和荧光显微镜技术,对斧文蛤精子超微结构与受精过程的细胞学变化进行了系统研究。电镜观察表明,斧文蛤精子为鞭毛型,全长45.2~47.7 μm,由头部、中段和尾部三部分组成。头部呈稍弯曲的狭茧形,长约2.5 μm,由顶体和细胞核组成,顶体呈圆锥形,内部中轴处有亚顶体腔;细胞核为长锥形,有核前窝和核后窝。中段由线粒体围绕中心粒复合体构成,5个近球形的线粒体呈单层梅花状排列;中心粒复合体由近端中心粒和远端中心粒组成,远端中心粒延伸出尾部的轴丝。尾部为细丝状鞭毛,内部的轴丝呈典型的“9+2”结构,外周有波浪状质膜包被。用荧光显微镜观察了斧文蛤受精及早期卵裂过程的细胞学变化,结果发现，斧文蛤成熟未受精卵呈圆球形,核相处于第一次成熟分裂中期;在水温27~28 ℃条件下受精,受精后6 min,精子入卵并膨胀成球形;受精后12~15 min、20~25 min受精卵排出第一、第二极体;30 min左右,精、卵核膨胀形成雄、雌原核;35 min,两性原核在卵子中央发生染色体联合;40~45 min,受精卵进行第一次卵裂,形成2个大小不等的分裂球;55~60 min,第二次卵裂结束,形成1大3小4个卵裂球,核相变化与第一次卵裂基本相同;75~80 min,第三次卵裂完成,自此次起开始进行螺旋分裂。另外,在斧文蛤受精过程中发现了约1%的多精入卵现象,其对成熟分裂和早期卵裂过程影响很大,常造成成熟分裂紊乱和第一次卵裂染色体分离异常。     

栉孔扇贝正常发育和人工雌核发育二倍体早期胚胎核行为的细胞学观察

采用Bouin氏液固定、石蜡切片和苏木精-伊红染色方法，在光镜下对栉孔扇贝正常发育和6-DMAP第二极体抑制型雌核发育二倍体卵在受精和第一、二次卵裂过程中的核相变化进行了详细观察。结果表明，正常发育卵内的雌、雄原核能融合为合子核，而雌核发育卵内的精核、雌核变化相当复杂。精核至少存在两种状态：（1）精核只在刚入卵时发生轻微膨胀，以后保持固缩状态，不膨大形成雄原核；（2）在第二次成熟分裂之后，精核再次去浓缩膨胀，但其体积并未达到正常雄原核的大小。在第一、第二次卵裂过程中，此精核不参与核分裂，以致密的染色质体（DCB）存在于两组分开的母本染色体之间，卵裂结束时滞留于两卵裂球的分裂沟上或进入其一的细胞质中。受精卵经6-DMAP处理，雌核形成第二极体的过程受到有效抑制，导致雌核二倍化。此外，作者对实验中出现的多精入卵和多极分离现象进行了观察和分析。     

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.     

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.     

Production of diatom–bacteria biofilm isolated from Seriola lalandi cultures for aquaculture application

Controlled incorporation of selected microalgae and bacteria in aquaculture systems can be beneficial because they can act as microbiological control. That is why the characteristics of biofilm generated naturally in Seriola lalandi culture cages were analysed, their potential benefit to the growth of larvae was studied, and their controlled use for improving the larval viability and as a vector to improve incorporation of previously studied probiotic bacteria was tested. According to biodiversity results, these biofilms are composed of a diatom–bacteria mix showing a decrease in biodiversity in laboratory culture conditions being dominated by Navicula phyllepta and bacteria of the family Rhodobacteraceae. This can be produced on mesh substrates incorporated in bioreactors with rapid growth rate and adhesiveness. Preliminary results from the addition of substrates with this specific biofilm in larvae culture systems showed that it is consumed by the larvae without negative effects, while positive effects on the viability of larvae in combination with probiotics were observed. Considering preliminary results, the addition of these specific substrates with diatom–bacteria biofilms could be a good improvement for aquaculture systems and together with the use of probiotics can contribute to maintaining a stable and controlled system improving the viability of the larval fish culture in its early stages.