Effects on growth and survival of loach (Misgurnus anguillicaudatus) larvae when co-fed on live and microparticle diets

The effectiveness of co-feeding loach ( Misgurnus anguillicaudatus ) larvae with live and microparticle diets on weaning performance was described here. Dry weight, total length, length and weight-specific growth rate (SGR) and survivals were monitored at 23–25 °C from the 4th day post hatching (dph) in different diet regimes, which included: microparticle diets (A), live cladocerans (B), enriched cladocerans (C), half microparticle diets plus half live cladocerans (D) and half microparticle diets plus half enriched cladocerans (E). The SGR (L and W) were significantly lower in treatment A than in other treatments after completing metamorphosis (day 4–20, P <0.05). On 30 dph, dry weight (mg) and total length (mm) were significantly lower in treatment A than in other treatments ( P <0.05). There were no significant differences in growth in treatments B, C, D and E before 30 dph. However, when live feed was withdrawn from 31–60 dph, in metamorphosed fish, there were significant differences ( P <0.05) among the treatments in survival and growth. Metamorphosed fish in treatment E had higher survival than the fish in other treatments at the end of the experiment. The SGR (L and W) of weaned fish in treatments B and C were similar but lower than in treatments A, D and E respectively. However, dry weight and total length in treatment A were significantly lower than in treatments D and E. It is suggested that weaning of M. anguillicaudatus from early development would appear to be feasible and that larval co-feeding improves the growth and the survival.     

饥饿对泥鳅某些血液指标的影响

对体长9·7~12·0cm、平均体重8·3g的泥鳅(Misgurnusanguillicaudatus)在正常摄食和饥饿4~16d状态下的血液指标进行了测定。结果表明:随着饥饿时间的延长,红细胞数量呈下降趋势,在饥饿的第4d、8d、12d和16d,红细胞数量分别是正常摄食时数量的67·5%,63·0%、61·3%和60·5%,差异极显著(P<0·01);红细胞的体积变大,饥饿到第16d时,红细胞的长径和短径分别比正常摄食时增加了2·8%和13·0%;白细胞数量呈上升趋势,在饥饿的第4d、8d、12d和16d,白细胞数量分别是正常摄食时数量的114·3%、121·7%、137·1%和139·4%;白细胞的体积逐渐变小,饥饿到第16d时,其长径和短径分别是正常摄食时的88·2%和89·4%,差异显著(P<0·05);血红蛋白含量在前8d的饥饿中是下降的,之后出现上升;红细胞的脆性在饥饿前期有所下降,后期则维持在一定水平;红细胞的沉降率随着饥饿时间的延长而有所加快,差异不显著。     

铜绿微囊藻和小球藻对水环境pH的影响

以盐碱池塘优势微藻铜绿微囊藻(Microcystis aeruginosa)、小球藻(Chlorella pyrenoidosa)为研究对象,采用正交实验方法,研究不同温度(20℃,25℃,30℃)和光照强度(2000 lx,4000 lx,6000 lx)组合条件下两种微藻对水环境pH的影响。结果显示,处于对数生长期的铜绿微囊藻和小球藻均能使水环境pH上升。在本实验范围内,不同温度和光照强度组合条件下,铜绿微囊藻的生长均能使水环境pH显著上升至9.50以上,在温度25℃、光照强度2000 lx条件下,藻密度达最大值1.1×10~7 cells/m L,水环境pH也达到峰值10.83;小球藻生长亦能使水环境pH的上升,并随温度升高、光照强度增强而增大,在温度30℃、光照强度6000 lx条件下,藻密度达最大值8.1×10~6 cells/m L,水环境pH也达到峰值7.73。通过ANCOVA分析,水环境pH和藻细胞密度呈正相线性相关,铜绿微囊藻水环境pH和藻细胞密度相关系数R~2=0.904,小球藻水环境pH和藻细胞密度相关系数R~2=0.903。与小球藻相比,同等藻密度的铜绿微囊藻更易使水环境pH显著上升(P0.01),是池塘养殖水体pH偏高的主要原因之一,本研究旨在通过控制藻相方式进行水环境调控,从而防止池塘pH偏高提供了基础数据。     

Comparison of haematology and serum biochemistry of cultured and wild Dojo loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>

Haematological and serum biochemistry parameters were studied and compared between cultured and wild ecotypes of Dojo loach Misgurnus anguillicaudatus during the prime fishing season, i.e. May–August. Data were analysed for the impact of feeding regime and other ecological conditions on the physiology of fish. The results revealed that haemoglobin, cholesterol, total protein, creatinine and uric acid levels in the two ecotypes were significantly different (n = 56, df = 54, P < 0.05). In addition, red blood cell, glucose, triglyceride and urea nitrogen levels were significantly higher in cultured individuals (n = 56, df = 54, P < 0.01) than in their wild counterparts. In contrast, the white blood cell level in cultured fish was significantly (n = 56, df = 54, P < 0.01) lower than that in the wild ones. These differences can be attributed to the physiological acclimatization of the fish to their living conditions and feeding regime, which influences the energy metabolism and, consequently, the health of the fish.     

Effects of different dietary vitamin C supplementations on growth performance,mucus immune responses and antioxidant status of loach (Misgurnus anguillicaudatus Cantor) juveniles

A 60‐day feeding trial was conducted to determine the effects of different dietary vitamin C levels on growth performance, immune response and antioxidant capacity of loach juveniles. Six isonitrogenous (58.6% of crude protein), isoenergetic (17.5 kJ g^?1) practical diets supplemented with 0 (VC0), 100 (VC100), 200 (VC200), 500 (VC500), 1000 (VC1000) and 5000 mg kg^?1 (VC5000) of VC (35% ascorbic acid equivalent) were fed to fish (mean initial weight 0.11 ± 0.02 g) in triplicate. Results showed that fish fed VC0 diet had significantly lower body weight gain (BWG) and survival rate (SR). However, BWG and SR improved significantly in fish fed VC100 and VC200 diet respectively. Whole body ascorbic acid concentration increased with incremental dietary VC levels from 0 to 100 mg kg^?1. The activity of mucus alkaline phophatase was significantly increased by the dietary VC level. Incremental levels of VC significantly reduced activities of glutathione peroxidase (GPx) and catalase. Moreover, fish fed diets containing more than 100 mg kg^?1 VC significantly down‐regulated the superoxide dismutase and GPx mRNA expression in liver. Meanwhile, the expressions of liver heat shock protein (HSP70) and nuclear factor‐erythroid 2‐related‐2 (Nrf2) were affected by fish fed diets containing VC from 100 to 5000 mg kg^?1. In conclusion, VC requirement of loach juveniles for optimum growth and functionally preventing lipid peroxidation was more than 200 mg kg^?1 of diet. Moreover, high dose of VC supplementation did not show any detrimental effects on loach growth performance.     

Effects of vitamin E supplementation on growth,lipid peroxidation and fatty acid composition of Dojo loach (Misgurnus anguillicaudatus Cantor) fingerlings

A high mortality of cultured loach during their early development has constrained loach aquaculture industry in China. The objective of this study was to evaluate the effects of dietary vitamin E (VE) supplementation on growth performance, lipid peroxidation and fatty acid composition of loach Misgurnus anguillicaudatus fingerlings. Six test diets supplemented with 0 (0E), 50 (50E), 100 (100E), 150 (150E), 200 (200E) and 500 mg kg^?1 (500E) of dl‐α‐tocopheryl acetate were fed loach fingerlings (mean initial weight 24.0 ± 0.2 mg) in triplicate for 40 days. Results showed that the fish fed diet 100E and 200E had significantly higher body weight gains and specific growth ratios and significantly lower feed conversion ratios compared with fish fed diet 0E. With the increase in dietary VE level, whole‐body VE content was significantly increased (except 500E) and thiobarbituric acid reactive substances value was significantly reduced. Increasing dietary VE level increased the percentages of 20:4n‐6 and 20:5n‐3 in neutral lipid fraction, but decreased the percentages of 20:4n‐6 and 20:5n‐3 in polar lipid fraction. In conclusion, VE requirement of loach fingerlings for optimum growth and functionally preventing lipid peroxidation was 136.1 mg kg^?1 of dry diet under the present experimental conditions.     

Effects of microalgal diets on larval growth and survival of Paphia malabarica chemnitz

The effects of food availability on the larval growth and survival of Paphia malabarica were studied in two experiments by feeding the larvae with six algal diets. Newly hatched larvae of P. malabarica were fed with six different marine microalgae species, singly and in a combination of two species. The best growth was with Isochrysis galbana and Nannochloropsis salina as a single species of diet. The nutritional value of single‐species diets was in the order of N. salina, I. galbana, Dicrateria inornata, Chaetoceros calcitrans, Tetraselmis gracilis and Dunaliella salina. Of the mixtures tested, 50%I. galbana/50%N. salina supported growth and metamorphosis equivalent to those of the I. galbana control.     

不同生态条件对泥鳅产卵、孵化及仔鱼培育影响初探

本文叙述在水温２６～２７５℃、水比重０９９８、ｐＨ６～７、ＤＯ７５～ｍｇ／Ｌ的情况下,泥鳅经ＨＣＧ注射后,分别放入底质为软泥、砂砾和玻璃的水族箱中产卵,软泥底优于玻璃底优于砂砾底;取４００粒受精卵分别放入比重为０９９８、１００５、１０１０、１０１５四个塑料盆中孵化,１００５以前能孵化出膜、以后不能孵化,但１００５仔鱼不能成活;取全长４３３ｍｍ４日龄仔鱼９４３尾分别放入三个同样大小的水族箱中,从第五日龄开始分别投喂轮虫、蛋黄和豆浆,经１９天培育,观察摄食情况,蛋黄最好,豆浆最差,活动能力,轮虫最强,豆浆最弱,生长速度,轮虫最快、豆浆最慢,成活率、轮虫最高、豆浆最低。     

Transpositional feeding rhythm of loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis> from larvae to juveniles and its ontogenesis under artificial rearing conditions

The diel feeding rhythm and ontogenesis during early life stage of loach Misgurnus anguillicaudatus were investigated under experimental conditions (light: L 06:00–18:00, D 18:00–06:00 h). Morphological and behavioral developments of loach from newly hatched to 40 days after hatching were observed. Larvae were able to prey on daphnia 3–4 days after hatching at 23 ± 0.5°C. As the larvae grew, they showed an increasing feeding capacity and a distinct feeding rhythm. Feeding intensity and incidence for day-4 larvae were highest at 10:00 and 16:00 h. The highest levels of feeding intensity for day-12 larvae occurred at 08:00, 12:00, and 18:00 h as did feeding incidence. By day 20, when the larvae metamorphosed, the highest levels of feeding intensity occurred at 06:00, 18:00, and 24:00 h and were concurrent with the highest feeding incidence. After metamorphosis, feeding capacity had again increased considerably and, in contrast to the earlier stages before day 20, feeding intensity for day-30 juveniles peaked at 05:00 and 20:00 h, about 1–2 h after the maximum feeding incidence. The feeding rhythm of loach juveniles at day 40 was almost the same as the day-30 juveniles. The estimated maximum daily feeding rates were 43.1%, 33.4%, 19.0%, 12.8%, and 5.8% of body weight on days 4, 12, 20, 30, and 40, respectively. Thus, loach was found to have different feeding rhythms in the pre- and post-metamorphosis stages, with the highest feeding activity in daytime during the larval planktonic stage before metamorphosis, and intensely nocturnal feeding behavior during the juvenile benthic stage after metamorphosis.     

不同饵料对美洲西鲱仔鱼生长、相关酶活力及体脂肪酸的影响

以美洲西鲱(Alosa sapidissima)仔鱼(孵化后10 d)为实验对象,在室内进行为期30 d的摄食生长试验,分别投喂不同的饵料[单独投喂卤虫(Artemia)、单独投喂微颗粒饲料、卤虫与微颗粒饲料混合投喂],分析不同饵料的投喂对存活、生长、消化酶活性、非特异性免疫相关酶活性以及体脂肪酸组成的影响。结果表明:(1)混合投喂组的存活与生长表现都要显著优于卤虫组和微颗粒饲料组(P0.05),微颗粒饲料组与卤虫组相比差异不大,而试验后期(20~30 d)微颗粒饲料组的存活与生长表现要优于卤虫组;(2)消化酶的结果显示,胃蛋白酶和淀粉酶活力在各组中无显著性差异(P0.05),胰蛋白酶、糜蛋白酶和脂肪酶在卤虫组中活力最低,显著低于其他两组(P0.05),其中糜蛋白酶和脂肪酶活性在微颗粒饲料组中要显著高于混合投喂组(P0.05);(3)碱性磷酸酶和超氧化物岐化酶活力在各组中无显著性差异(P0.05),过氧化氢酶和溶菌酶活力在微颗粒饲料组中最高,卤虫组中最低,两者之间差异显著(P0.05);(4)鱼体脂肪酸受饵料脂肪酸组成影响较大,微颗粒饲料中n-3HUFA和DHA含量较高,其投喂后在鱼体中的含量也高。综上所述,不同饵料投喂对美洲西鲱仔稚鱼存活、生长、消化酶活性、非特异性免疫相关酶活性以及体脂肪酸影响显著,在试验20 d之前使用卤虫与微颗粒饲料混合投喂,20 d后完全转食微颗粒饲料,可以降低成本,同时提高生产效率。     

Comparative growth of Pacific oyster (Crassostrea gigas) postlarvae with microfeed and microalgal diets

Two trials were carried out in the laboratory in order to assess the effect of microparticulated feed (F) and live (Thalassiosira pseudonana, M) diets on the growth of recently set (396 ± 13 μm shell height) and 2 mm Crassostrea gigas postlarvae. Different proportions of M and F (100:0, 75:25, 50:50; 25:75, 0:100) were delivered in a single dose of 3 h d⁻¹ in trial 1. Dietary M:F proportions of 100:0, 50:50, and 0:100 were delivered as a single pulse of 8 h d⁻¹ (P1) or two pulses of 4 h⁻¹ (P2) in trial 2. Maximal daily M ration was 296 cells μl⁻¹ d⁻¹ (trial 1), 150 M cells μl⁻¹ d⁻¹ (trial 2), or their equivalent F dry weight. Shell height (SH), dry (DW), and organic weight (AFDW) were evaluated weekly. Oysters from trial 1 significantly increased their size after 28 days, and exhibited no significant dietary differences in terms of DW (1.21 ± 0.15 to 2.01 ± 0.28 mg) or AFDW (0.091 ± 0.022 to 0.166 ± 0.029 mg). Newly set postlarvae (trial 2) also exhibited significant growth after 25 days. No dietary differences were observed in trial 2, yet P2 oysters attained significantly higher shell heights (825–912 μm) than P1 oysters (730–766 μm) after 25 d. Pulse effects were marginally not significant in terms of AFDW and growth rate. Together, these findings showed that balanced microfeeds have a practical potential for the culture of early C. gigas postlarvae, when they are delivered in pulse-feeding schemes     

Effects of cell-cycle arrest agents on cleavage and development of loach (Misgurnus anguillicaudatus) embryos

The aim of this study was to determine the lowest concentration of nocodazole and colchicine to arrest blastomere division during the cleavage stage of loach embryos and to assess the reversibility and toxicity of the treatments in the treated embryos. Eight-cell loach embryos were incubated for 4, 8, 12, or 16 h in 1/10× Holtfreter supplemented with either nocodazole, an inhibitor of tubulin polymerization, or colchicine, an inhibitor of tubulin assembly. Complete arrest of cell cycle was observed, at a colchicine concentration of 0.996 mM and at a nocodazole concentration of 0.275 μM, respectively (the lowest effective concentration). No major morphological alteration in chromatin was observed. Reversibility and toxicity of both agents were dose and exposure period dependent. For both agents, prolonging cleavage arrest for more than 4 h (at the effective concentrations) is detrimental to development of embryos. Nocodazole treatment was less cytotoxic, whereas the concentrations of colchicine which induce cleavage arrest were detrimental to development beyond the blastula stage. Toxic effects beyond the blastula stage could be minimized for both agents by reducing the period of treatment and concentration. This revised version was published online in August 2006 with corrections to the Cover Date.     

近交对长牡蛎幼虫和稚贝生长与存活的影响

分别以2010年通过2个野生个体进行交配获得的A01全同胞家系和2011年通过A01家系子代进行交配获得A02全同胞家系为亲本,在2013年6月采用同时建立全同胞交配子一代F1(F=0.250)、全同胞交配子二代F2(F=0.375)及设置对照组(F=0)的方法,研究在相同环境条件下,不同实验组的受精率与孵化率以及近交对长牡蛎幼虫期、稚贝期生长和存活的影响,并初步探讨近交代数与近交衰退的关系。结果发现,各组的受精率均在90%以上,除F2组外其余2组的孵化率也在90%以上;幼虫阶段,F1组和F2组的壳高与壳长均从12日龄出现衰退(近交衰退系数,inbreeding depression coefficient,IDC0),且F2组壳高的近交衰退系数均小于同日龄F1组壳高的近交衰退系数;F1组和F2组的存活率在整个幼虫期间均出现衰退,且F1组和F2组存活率的近交衰退系数均随着幼虫日龄的增加而逐渐减小。稚贝阶段,F1组和F2组的平均壳高在各日龄均表现出近交衰退(IDC0),且F2组壳高的近交衰退系数均小于相同日龄F1组壳高的近交衰退系数;3个实验组的平均壳长在整个稚贝阶段无显著性差异;F1组和F2组存活率的衰退在不同日龄始终存在(IDC0),且随着稚贝日龄的增加其衰退程度逐渐加大。研究结果为长牡蛎选择育种和遗传改良提供了基础资料。     

Lipid enrichment for Senegalese sole (Solea senegalensis) larvae: effect on larval growth, survival and fatty acid profile

Results from three larval Senegalese sole (Solea senegalensis) feeding trials using non-enriched Artemia and Artemia enriched with Super HUFA®, Arasco®, sunflower oil and microalgae are presented and the effects on larval survival, growth and fatty acid (FA) composition are reported. The FA profile of Senegalese sole eggs was analysed to gather information about the nutritional requirements of the early larval stages and a quite high DHA/EPA ratio (4.3) was found. However, there was no evidence of a high dietary demand for DHA or EPA, given that no relationship was found between dietary HUFA concentration and larval growth and survival. When larvae were fed non-enriched Artemia a significantly better growth and comparable survival were obtained than with Artemia enriched with Super HUFA® (containing the highest HUFA level and DHA/EPA ratio). The FA profiles of the larvae generally reflected those of their diets. DHA was an exception, as it was present in high proportions, even in larvae fed DHA-deficient prey. Total FAME concentration decreased during larval development, with SFA, MUFA and PUFA being equally consumed; HUFA appeared to be less used, with its relative concentration being either kept constant (particularly EPA and ARA) or increased (DHA). A specific requirement for ARA in the first larval stages could not be confirmed but it was always present in considerable amounts, even in larvae fed an ARA poor diet.     

Individual growth variation and its relationship with survival in juvenile Pacific oysters, Crassostrea gigas (Thunberg)

In order to study individual growth variability and its relationship with survival in juvenile Crassostrea gigas, parental oysters were sampled at four sites located along the French Atlantic coast and bred under controlled hatchery conditions. Four groups of larvae were obtained by crossing five males and five females from each of the four sites, and a fifth group by crossing these 20 males and 20 females together in a pool. Larvae were reared under conditions allowing the maintenance of a maximum variability of size and gave five experimental groups. Oysters were individually monitored for growth and survival from 3 to 10 months after fertilization. The individual growth performances were relatively stable over time and no noticeable compensation for growth occurred. Early growth rate was a very good predictor of size later in life: 66% of variation in the live weight at 10 months could be explained by variation in the initial growth rate calculated between 3 and 4 months. A significant group effect was observed on survival and on growth rate. Mortality mostly occurred between 3 and 5 months and appeared to affect the slow-growing animals more. However, two groups can be distinguished among those which died during the experimental period, one which showed a decrease in weight and the other whose growth was similar to surviving oysters. These results are discussed in the light of usual oyster farming practices and selective breeding. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of dietary protein and lipid levels on growth performance,fatty acid composition and antioxidant‐related gene expressions in juvenile loach Misgurnus anguillicaudatus

Dojo loach (Misgurnus anguillicaudatus) is one of the most important cultured freshwater fish in several East Asian countries. However, a little information is available in its nutritional requirements. Thus, this study was conducted to evaluate the effects of feeding varying levels of dietary protein and lipid on growth, fatty acid composition and antioxidant‐related gene expressions in juvenile loach. Six practical diets at three levels of protein (30%, 40% and 50%) and two levels of lipid (6% and 12%) were fed to loach juveniles (initial weight 0.40 g) in triplicated groups (20 fish per replicated) for a period of 8 weeks. Results showed that regardless of lipid level, body weight gain of fish was significantly increased with incremental dietary protein level. Meanwhile, feed conversion ratio was significantly decreased by dietary protein levels, and the lowest value was observed in fish fed dietary protein levels of 50%, regardless of dietary lipid level. Moreover, the percentage of 22:6n‐3 in viscera was significantly increased by different protein levels. The expression level of catalase was significantly increased with incremental dietary protein level with both lipid levels. Meanwhile, the expression level of hepatic nuclear factor erythroid 2‐related factor 2 (Nrf2) was downregulated with incremental dietary protein level with 6% of lipid level, but the expression was upregulated with incremental dietary protein level with 12% of lipid level. In conclusion, these data suggested that 6% lipid and 50% protein in diet was optimal for loach during early development stage.     

光照对红条鞭腕虾繁殖性能及饵料对其幼体生长发育的影响

为了深入了解光照对红条鞭腕虾(Lysmata vittata)亲虾抱卵情况的影响,本研究通过将正常光照组(12L∶12D)亲虾的抱卵率与全暗(黑)组进行对比,发现正常光照组红条鞭腕虾亲虾抱卵率为(95.8±3.6)%,而全暗(黑)组的抱卵率为0,正常光照组亲虾的抱卵率显著高于全暗(黑)组(P0.05),表明适宜的光照强度对红条鞭腕虾亲虾抱卵行为起到促进作用。本研究还对比分析了投喂不同生物饵料对红条鞭腕虾溞状幼体成活率和生长发育周期的影响。结果发现,投喂丰年虫(Artemia nauplii)和蒙古裸腹溞(Moina mongolica Daday)混合组的溞状幼体成活率为(38.3±2.3)%,幼体经过25～29 d全部发育成仔虾;而单一投喂丰年虫组的溞状幼体成活率为(26.8±4.9)%,幼体经过37～41 d全部发育成仔虾;混合组的溞状幼体成活率显著高于单一组(P0.05),且其幼体的生长周期也明显短于单一组,表明投喂丰年虫和蒙古裸腹溞混合饵料比只投喂丰年虫饵料更有利于幼体的存活和发育。此外,本研究还观察和详细描述了红条鞭腕幼体发育过程的形态和结构变化特征,并将它分为溞状幼体1～9期等9个不同时期,幼苗经过9期溞状幼体期后通过蜕皮最终变态为红条鞭腕虾仔虾。本研究对丰富鞭腕虾属虾类的生殖生物学理论和开展其人工繁育研究具有重要的指导意义。     

Effects of water depth on survival and growth of <Emphasis Type="Italic">Argopecten purpuratus</Emphasis> (Lamarck, 1819) spat in northern Chile

Collection and suspended culture of Argopecten purpuratus spat in Japanese-type collectors was undertaken in the Rinconada Marine Reserve (Antofagasta, Chile) to determine growth variations between surface and bottom waters. Scallop spat was collected at 16-m depth and grown at 1- and 16-m depths. An initial settlement of ca. 13,000 post-larvae per bottom collector (2 cohorts) was observed on 3 February 2001. Two new cohorts settled in bottom collectors on 3 March, while no spat settlement occurred in surface collectors. The four cohorts exhibited substantial and different mortality rates over the study period, depending on the cohort and on-growing depth. The first and second cohorts exhibited mortality rates of 80.3 and 53.1% in bottom collectors, respectively, versus 29 and 43.6% in surface structures. The third and fourth cohorts exhibited mortality rates of 21.4 and 59.7% in bottom collectors, respectively. Mean shell height of scallop spat after 88 days of culture was 6.46 mm for the first cohort and 4.37 mm for the second cohort in bottom collectors, versus 10.33 and 7.31 mm in surface collectors, respectively. Mean post-larval growth rate in bottom collectors (86 μm day⁻¹) was significantly lower than growth rate in surface collectors (146 μm day⁻¹). Factors explaining the depth-related mortality and growth rates are discussed to improve scallop culture in the Reserve. It was concluded from the results that culture improvement in Antofagasta Bay would require collecting spat in bottom waters and raising it near the surface during initial cultivation stages.     

Effects of water exchange regimes on growth, survival and shell normality of the hatchery reared juvenile spotted babylon (Babylonia areolata Link 1807) in a recirculating seawater system

Growth, survival and shell normality of hatchery reared juvenile Babylonia areolata were examined at four water exchange regimes of 0, 15, 30 and 60 day intervals in a recirculating seawater system over a 120 day experimental period. Higher body weight gains and shell length increments were observed in snails held at water exchange of 15 day intervals, especially when compared with those held at water exchange of 60 and 0 day intervals (P < 0.05). Water exchange affected the final survival of B. areolata. At the end of the experiment, final survival rates were 65.47 ± 0.66%, 87.48 ± 0.67%, 86.34 ± 0.92% and 78.50 ± 3.26% for snails held in the water exchange treatments of 0, 15, 30, and 60 day intervals, respectively, and those of shell abnormality were 97.65 ± 1.04%, 93.09 ± 2.34%, 97.08 ± 1.18% and 96.71 ± 1.84%, respectively. The present study concluded that water exchange regimes of the recirculating system influenced growth, survival, shell normality and water quality of the recirculating culture system for this species.     

Natural food and artificial,dry starter diets: effects on growth and survival in intensively reared European grayling

Four artificial, dry feeds and two diets consisting of natural, live food were evaluated for use as starter diets in the intensive rearing of European grayling (Thymallus thymallus). Long-term effects of the different diets were also studied. The investigation was divided into two parts: a 14 day starter period and the subsequent 115 days, during which the long-term effects were studied. Diets differed between the different treatment groups during the initial 2 weeks, whereafter all fish were offered a single diet. At the end of the starter period, significant differences in weight (p<0.001) were obtained between natural (control) feed groups and three of the artificial feed groups. The highest growth rate (9.6% day^–1), and length increase (9 mm) as well as the lowest mortality rate (6.0%) were obtained with one of the artificial diets. Growth rate, length increase and mortality of grayling in the other diet groups varied from 3.6 to 7.7% day^–1, 5 to 7 mm and 7.0 to 9.1%, respectively. The switchover to a different dry diet resulted in an increase in mean daily mortality for all groups previously fed a dry diet. For the fish previously fed live food the mortality rate remained about the same. Groups of fish growing slowly during one period seemed to compensate for their initially low growth by increasing their growth rates during the next period. The highest mean daily mortality for all groups during the experiment was observed during the period with the highest water temperature. It was concluded that European grayling can be intensively reared during the start-feeding phase on artificial as well as natural diets, and that artificial dry diets can be used exclusively throughout the first summer.