Effects of Dietary Protein and Energy Levels on Growth and Body Composition of Juvenile Flounder Paralichthys olivaceus

A feeding trial of three protein levels (30, 40 and 50%) and two energy levels (300 and 400 kcal/100-g diet) factorial design with three replications was carried out to investigate the proper dietary protein and energy levels for the growth of juvenile flounder Paralichthys olivaceus . Weight gain of fish tended to improve with increasing dietary protein level. Weight gain of fish fed either the 40% or 50% protein diet with 300 kcal/100-g diet was significantly higher ( P < 0.05) than with 400 kcal/100-g diet. The best weight gain was obtained from fish fed the 50% protein diet with 300 kcal/100-g diet. Feed efficiency tended to improve with increasing dietary protein level. However, dietary energy level had no significant effect on feed efficiency of fish fed the 30% or 50% protein diet, but that of fish fed the 40% protein diet with 300 kcal/100-g diet was significantly higher than with 400 kcal/100-g diet. Protein retention tended to increase as dietary protein level increased and energy level decreased. Lipid content of fish fed the diet containing 400 kcal/100-g diet was significantly higher than that of fish fed the diet containing 300 kcal/100-g diet at all protein levels. Fatty acid compositions such as linoleic acid, EPA (20:5n-3) and DHA (22:6n-3) offish were directly affected by dietary lipid (squid liver oil and/or soybean oil) used for energy source. Based on the above results, it can be concluded that the proper dietary protein and energy levels for the growth of juvenile flounder are 50% and 300 kcal/100-g diet, respectively.     

Development of Aquaculture Methods for Southern Flounder,Paralichthys lethostigma

ABSTRACT

A detailed spawning and larval rearing protocol for the production of southern flounder, Paralichthys lethostigma, is presented. The protocol is based on the results of spawning, larval culture and fingerling production trials with the southern flounder, which were completed during 1998 and 1999. Seventy-six brood fish (0.1-3.8 kg) were collected from the wild, acclimated to captivity, and stocked in matura tion tanks. Sex ratio (male:female) was 1.1:1. Males (0.1-1.0 kg; mean = 0.5 kg±0.30 SD) were significantly smaller (P > 000.1) than females (0.5-3.8 kg; mean =1.8 kg±0.75 SD). Spermatogenesis was achieved using temperature manipulation during a 3-month period. Vitellogenesis was nearly completed when most females were caught, and final ovulation was accomplished using gonadotropin releasing hormone-analogue (GnRH-a) implants and human chorionic gonadotropin (HCG). Eggs were obtained from both tank and strip spawnings. At 24-26°C, fertilized eggs hatched within 24-28 hours. Weaning to artificial diets was completed after 5 weeks, when metamorphosis was completed. Epizootics of Vibriosis and Amyloodinium ocellatum caused massive mortalities. Average survival rate from eggs to fully metamorphosed fingerlings was 30%, ranging from 5-40%. A total of 14,562 juveniles measuring 5 cm were produced in these experimental trials. Approximately 25% of the fingerlings exhibited pigment abnormalities known as hypomelanosis or pseudo-albinism on the dark side and hypermelanosis or ambicoloration on the blind side. Reversed asymmetry was observed in 5% of the fingerlings and a few individuals (0.02%) exhibited no ocular migration at all. A large size variation was observed during early larval development stages, with larger individuals growing faster through post-larval, juvenile, and adult stages. Results suggest that hatchery production of southern flounder fingerlings should rely on early culling of runts.     

循环养殖系统中牙鲆生长及营养盐状况研究

研究了一个包括鱼池、沉淀池、硝化滤器和大型海藻滤器的循环养殖系统长期运行的水质状况及养殖牙鲆的生长状况。报道了该系统中的牙鲆在一定时间内的生长情况,建立了牙鲆体重(抽样平均湿重)与生长时间的回归方程:W=4.654 e0.0181 t。同时监测系统中的NH4 -N、NO2--N、NO3--N、PO43--P浓度,其NH4 -N在实验时间内一直保持在0.4 mg/L以下,NO2--N低于0.2 mg/L以下,NO3--N、PO43--P在开始时有一定积累,后来有下降趋势。实验表明,该循环养殖系统可以满足牙鲆工厂化循环养殖的要求。     

Effects of Dietary Protein and Lipid Levels on Growth and Body Composition of Juvenile Japanese Flounder,Paralichthys olivaceus,Fed Diets Containing Intact Proteins or Crystalline Amino Acids

Abstract

The influence of eight semi-purified diets having different protein and lipid levels on growth performance and body composition of Japanese flounder, Paralichthys olivaceus, was evaluated. The sources of protein were either intact protein (IP) or a mixture of IP and crystalline amino acids (CAA). In trial 1 (IP group), four test diets were prepared from IP sources (casein-gelatin) with combination of two protein levels (35% and 50%) and two lipid levels (10% and 20%). In trial 2 (PA-group), another four test diets were formulated using IP and CAA with combination of the same two protein and two lipid levels as used for trial 1. The juveniles (about 2.00 g initial weight) were fed the respective test diets for 42 days in duplicate tanks. In both trials, weight gain was the highest for juveniles fed the diet containing 50% protein with 10% lipid and the lowest in those fed the 35% protein with 10% lipid diet. Weight gain of juveniles was significantly increased when the lipid levels were increased in low protein (35%) diets for both trials. In high protein (50%) diet, however, increase lipid levels from 10 to 20% with 50% protein resulted in decrease in weight gain, irrespective of protein sources. Specific growth rate, feed intake, feed conversion efficiency were significantly affected by different dietary protein and lipid level. Content of neutral lipids in the whole-body particularly, triglycerides was statistically higher for fish fed the high-lipid diets than those fed the low-lipid diets irrespective of protein sources. But, polar lipid did not show any differences either for different protein or lipid levels. Level of individual amino acids in the whole-body showed little difference among the dietary treatments. Results suggest that Japanese flounder grew better on low lipid level with 50% protein-based diets and supplementation of CAA did not show any adverse effect on the growth performance with different levels of protein and lipid in the diets.     

淡水闭合循环养殖条件下养殖密度和个体大小对漠斑牙鲆(Paralichthys lethostigma)幼鱼生长的影响

以新疆伊犁河生态渔业中心漠斑牙鲆循环水养殖系统为实验平台，在生产规模上研究了闭合循环淡水养殖条件下养殖密度和个体大小对漠斑牙鲆幼鱼生长的影响。结果表明：漠斑牙鲆池底覆盖率低于34％时，养殖密度对漠斑牙鲆生长的影响不显著（P〉0．05）；养殖密度对个体大小的分化具有显著影响（P〈0．05），加强养殖管理可以降低该影响；漠斑牙鲆全长120mm时，性别分化基本完成，雄鱼规格和生长速度明显低于雌鱼。     

饲料蛋白质和能量水平对草鱼生长和鱼体组成的影响

采用3×3因子试验确定不同蛋白质和脂肪水平饲料对草鱼生长和鱼体组成的影响。初始平均体质量为0.75g的试验鱼放养在27个规格为85cm×35cm×95cm的网箱中,每箱放养50尾。日粮中的蛋白源、脂肪源和可消化碳水化合物源,分别采用鱼粉、豆油和糊精配制,日粮设3个粗蛋白水平,每个蛋白水平有3个能量水平饲养草鱼84d。结果表明MPLL组(粗蛋白为30%,粗脂肪为4%)的特殊生长率和蛋白质效率最高,饲料系数最低,但与LPML组(粗蛋白为25%,粗脂肪为6%)差异不显著;总的来看,脂肪含量在4%和6%时特定生长率和饲料系数以中蛋白质组(MP,30%)最高,脂肪含量在8%时特定生长率和饲料系数以低蛋白质组(LP,25%)最高,表明饲料脂肪水平对鱼的生长和饲料系数有显著影响。随着饲料可消化能的增加,鱼体的脂肪含量增加,而蛋白和灰分含量没有多大变化。综合饲料成本等因素,本试验初步确定草鱼幼鱼生长所需的最适蛋白水平为25%,DP/DE约为23.47mg·kJ-1。     

不同蛋白水平饲料对台湾东风螺生长性能和体组成的影响

以优质鱼粉、豆粕等原料制成蛋白质含量不同的6组饲料(粗蛋白含量分别为48.16%、45.64%、40.67%、35.68%、30.80%、25.96%),喂养台湾东风螺47 d,以投喂鲜杂鱼组作为对照,分别于15、27、37、47 d测定螺高、螺宽、螺体重等生长指标,计算不同处理组在不同时间段(27、37、47 d)的饲料系数和蛋白质效率,试验结束后测定东风螺螺肉的体组成和氨基酸含量,研究结果表明:投喂颗粒饲料比投喂鲜杂鱼的饲料系数显著高;而当颗粒饲料中蛋白质含量变化(25%~48%)时,对东风螺生长性能并无显著影响。但随着饲料蛋白含量的增加,东风螺对饲料的利用率在一定程度上有所提高。当饲料中粗蛋白含量低于25%时,47 d时其饲料系数2.3,显著高于其他饲料组;蛋白质效率1.74显著低于蛋白含量48.16%饲料组。从东风螺生长性能和饲料利用分析,颗粒饲料中蛋白质含量不应低于25%。所有组东风螺螺肉的粗蛋白、脂肪,总氨基酸组成均无显著差异,但是一些中性氨基酸(如亮氨酸、异亮氨酸和丙氨酸)和精氨酸随着饲料蛋白含量的降低而呈现出降低趋势,部分组产生了显著差异。投喂颗粒饲料的东方螺生长不如投喂鲜杂鱼组。     

饲料蛋白水平对眼斑双锯鱼幼鱼生长性能和体成分的影响

为确定眼斑双锯鱼幼鱼人工配合饲料中合适蛋白水平,试验研究了饲料蛋白水平对眼斑双锯鱼幼鱼生长、饲料转化率和体成分的影响。养殖试验在循环水系统中进行,初始体质量为(0.085±0.002)g的幼鱼随机分配到6个处理组(每组3个平行,每个平行40尾),分别投喂蛋白水平38.11%、40.91%、44.16%、47.21%、50.02%和53.16%的人工饲料,试验持续56d。不同蛋白水平饲料对眼斑双锯鱼幼鱼质量增加率、特定生长率、饲料系数、蛋白质效率以及全鱼的体成分等均有显著影响。饲料蛋白水平为38.11%~50.02%时,随着饲料蛋白水平的增加,眼斑双锯鱼幼鱼的质量增加率和特定生长率呈增加的趋势,饲料蛋白水平为53.16%时略有下降。经回归分析,当饲料蛋白水平为51.8%时,质量增加率最大;蛋白水平为51.1%时,特定生长率最大。饲料系数也随着饲料蛋白水平增加而呈现先降后升的趋势,饲料系数谷值出现在蛋白水平为47.21%试验组,而蛋白质效率则相反。经回归分析,当饲料蛋白水平为47.5%时,饲料系数最小;饲料蛋白水平为47.8%时,蛋白质效率最大。全鱼粗蛋白随饲料蛋白水平升高呈增加趋势,但到一定水平后维持该水平不再增加,而粗脂肪则随饲料蛋白水平升高呈先降后升的趋势。综合生长、饲料转化率和体成分等指标,本试验条件下眼斑双锯鱼幼鱼适宜的饲料蛋白水平为47.5%~51.8%。     

Effect of Dietary Protein and Lipid Levels on Growth and Body Composition of Spotted Halibut,Verasper variegatus

A 83‐d feeding experiment was undertaken to evaluate the effects of dietary protein and lipid levels on growth and body composition of spotted halibut, Verasper variegatus (initial average weight of 93.0 ± 1.0 g). Nine diets were formulated to contain three protein levels (40, 45, and 50%), each with three lipid levels (8, 12% and 16%). Each diet was randomly fed to triplicate groups of 20 fish per tank in the indoor culture system. Results showed that the survival rate of fish was not significantly affected by protein and lipid levels (P > 0.05). Weight gain, specific growth rate (SGR), and feed intake (FI) significantly decreased with the increasing dietary lipid levels (P < 0.05). Feed efficiency significantly increased while the feed conversion ration significantly decreased with increasing dietary protein levels (P < 0.05). Weight gain, SGR, FI, and feed efficiency of fish fed 50% protein and 8% lipid were significantly higher than that of the other groups. For each level of dietary lipid, the increase in dietary protein resulted in significant increases in whole‐body crude protein (CP) contents (P < 0.05); the increase in dietary lipid caused significant increases in whole‐body crude lipid content and gross energy at each protein level (P < 0.05). The muscle CP, lipid, and gross energy had the same tendency. The results of this study indicated that increasing dietary lipid levels did not result in a protein‐sparing effect. It could be recommended that the proper dietary protein and lipid levels of spotted halibut were 50 and 8%, respectively.     

饲料蛋白质和能量水平对草鱼幼鱼生长和消化酶活性的影响

在水温24～29℃下,将675尾规格整齐、健康、体质量为（35.59士0.44）g的草鱼（Ctenopharyngodon idel-lus）随机分为9个处理,每处理3个重复,放养于水泥池中的网箱（100cm×50cm×100cm）内,投喂以鱼粉和豆粕为蛋白源,豆油作为脂肪源配制的3个蛋白水平（24%、28%、32%）,每一蛋白水平设3个脂肪水平（4%、6%、8%）,共计9种饲料。饲料蛋能比（P/E）在15.81-22.46 mg·kJ-1之间。92d的饲养表明：D4组（蛋白质含量为28.02%,脂肪为4.30%）草鱼的特定生长率最高,显著高于其他各组（P〈0.05）。随着饲料中蛋白含量的增加,草鱼全肠中蛋白酶的活力逐渐升高,之后又降低,以D4组饲料的蛋白酶活性最高,显著高于D1、D8和D9（P〈0.05）。本实验表明,该生长阶段的草鱼所需最适蛋白水平为28.02%,能量为14307kJ.kg-1,P/E约为19.58mg·kJ-1。     

Diet and Light Intensity Effects on Survival, Growth and Pigmentation of Southern Flounder Paralichthys lethostigma

Interest in the culture of flatfishes has increased globally due to high consumer demand and decreased commercial landings. The Southern flounder Paralichthys lethostigma inhabit South Atlantic and Gulf of Mexico waters and support important commercial and recreational fisheries. In spring, 1996, a two-part larval rearing study was performed with Southern flounder to examine the effects of three larval diets and two light intensities on survival, growth, and pigmentation. The first part of the study consisted of feeding 6 d post-hatch (dph) (3.0 ± 0.1 mm TL) larvae three diets: 1) rotifers Brachionus plicatilis at a rate of 10/mL from day 1–9 and Artemia nauplii (3/mL) from day 7 through metamorphosis; 2) rotifers fed day 1 through metamorphosis and Artemia fed day 7 through metamorphosis; or 3) same diet as treatment 1 plus a commercial larval diet added day 13 through metamorphosis. The second part of the study examined the effects of two light levels: low-light (mean 457 lux) and high-light (mean 1362 lux). At 24 C, metamorphosis began on day 23 (mean fish size 8.2 ± 0.6 mm TL) in all treatments and was completed by day 30. Analysis of survival, size, and pigmentation data indicated there were no significant differences among feed treatments or between light treatments. Overall survival was 33.4% (±15.9) and mean length was 11.5 mm TL ± 1.3. Only 35% of the larvae were normally pigmented. Reexamination of the pigmentation on day 37 indicated fish reared at the low light intensity through metamorphosis (day 30) but exposed to high light intensity for 1 wk post-metamorphosis had become significantly more pigmented.     

Effect of Dietary Inclusion of Blue Mussel Extract on Growth and Body Composition of Japanese Flounder Paralichthys olivaceus

Dietary inclusion of a water-soluble fraction of blue mussel Mytilus galloprovincialis was examined as a feeding stimulant for juvenile Japanese flounder Paralichthys olivaceus . The control diet mainly consisted of fish meal, potato starch, and pollack liver oil. Five, 10, and 20% (weight/weight) of the control diet was exchanged with aqueous extracts of blue mussel meat in experimental groups. Fish of about 10 g in initial body weight were fed each diet to satiation, twice daily, 6 d per wk for 6 wk at 20 C. The final body weight, weight gain, and feed efficiency of fish fed the diets containing blue mussel extracts were significantly higher than those of fish fed the control diet. However, these parameters were not different among experimental groups containing blue mussel extract independent of the inclusion level of extract. A similar trend was shown in protein efficiency ratio as fish fed the control diet had a significantly lower protein efficiency ratio than the other dietary groups. Compared to the control diet, higher plasma protein and lower triglyceride were found in fish fed the diets with the extract, while other blood constituents were relatively similar for the dietary groups tested. On the other hand, whole-body crude lipid content and lipid retention of fish fed the diets with the extract were generally significantly higher than those of fish fed the control diet. Whole body crude protein was identical regardless of the dietary composition; however, protein retention of fish showed a similar trend to lipid retention.     

漠斑牙鲆人工催产和自然产卵的比较

为探索漠斑牙鲆人工催产的可行性,以便在预期时间集中获得苗种,分别于2006年在大连和2007年在江苏进行了人工催产和自然产卵对比试验.试验结果表明,漠斑牙鲆亲鱼自然产卵受精率和孵化率远远高于人工催产,但人工催产可以准确掌握生产时机,在短时间内获得大量受精卵和初孵仔鱼;4龄亲鱼人工催产产卵量、受精率、受精卵孵化率高于3龄亲鱼.人工催产受精率孵化率有待于进一步提高.     

容器颜色对漠斑牙鲆白化率和成活率的影响

本文就培养容器的颜色对漠斑牙鲆稚鱼的白化率和生长率的影响进行初步研究。结果表明:用深蓝色和黑色等深色容器培养的稚鱼白化率显著低于白色和黄色等浅色容器(p<0.05),黑色、深蓝色、黄色和白色4个组别(N=100)的白化率分别为20.8%、14.4%、57.6%和86.6%;白色最高为86.6%,深蓝色最低为14.4%;而用不同颜色的容器培养漠斑牙鲆的稚幼鱼,对其成活率影响不大(p>0.05),黑色、深蓝色、黄色和白色4个组别的成活率分别为96.0%、90.0%、82.5%、93.0%;白化稚幼鱼的生长发育并无异常。     

Effects of Temperature on Egg Hatch,Larval Growth and Metamorphosis for Hatchery-Cultured Southern Flounder,Paralichthys lethostigma

ABSTRACT

Egg hatch, larval growth, and metamorphosis of southern flounder, Paralichthys lethostigma, were examined at 13, 17, 21, and 25°C in laboratory experiments. The experiments were separated into four developmental phases: (1) from fertilization until hatch; (2) from hatch until mouth opening; (3) from first feeding until the onset of metamorphosis; (4) from the onset until the completion of metamorphosis. Time to egg hatch were 109, 58, 39, 30 hours at 13, 17, 21, and 25°C, respectively. Size at hatch varied little among temperatures, while percent hatch was significantly higher at 17°C (P < 0.05). There was no significant difference in total length at mouth opening among temperatures (P > 0.05). However, those larvae raised at higher temperatures reached mouth opening earlier, as it took on average 7.4, 3.9, 2.8, and 2.2 days from hatch at 13, 17, 21, and 25°C, respectively. During phase three, the growth rate was optimal at 17°C, as growth rates were 0.046, 0.110, 0.106 and 0.096 mm/day at 13, 17, 21, and 25°C, respectively. Larvae in phase four completed metamorphosis sooner at higher temperatures than at lower temperatures. It took 26.4, 15.7, and 13.1 days to complete metamorphosis at 17, 21, and 25°C, respectively, while only 16% of those at 13 progressed to stage “G” within the 27 days that phase four encompassed. No difference in total length was found among treatments (P > 0.05) at the completion of metamorphosis, but fish in the 21 °C treatment had a significantly higher survival (P < 0.05). It can be concluded that southern flounder could be produced in the highest quantity and at the largest size by raising them at 17°C from fertilization until the onset of metamorphosis, and at 21 °C during metamorphosis.     

Effects of Dietary Chlorella ellipsoidea Supplementation on Growth, Blood Characteristics, and Whole-Body Composition in Juvenile Japanese Flounder Paralichthys olivaceus

The study was conducted to investigate the effects of dietary Chlorella powder (C) supplementation on growth performance, blood characteristics, and whole-body composition in juvenile Japanese flounder Paralichthys olivaceus . Four experimental diets were supplemented with C at 0, 1, 2 and 4% (C₀, C₁, C₂, and C₄) on a dry-weight basis. Three replicate groups of fish averaging 1.13 ± 0.02 g (Mean ± SD) were randomly distributed in each aquarium and fed one of four experimental diets for 12 wk. After 12 wk of the feeding trial, fish fed C₂ diet had higher weight gain (WG), feed efficiency (FE), and protein efficiency ratio (PER) than did fish fed C₀ and C₁ diets ( P 0.05); however, there was no significant difference among fish fed C₁ and C₄ diets, and among fish fed C₂ and C₄ diets ( P > 0.05). Fish fed C₂ and C₄ diets had a lower serum cholesterol level than did fish fed C₀ and C₁ diets ( P 0.05). Fish fed C₂ and C₄ diets had a lower body fat than did fish fed C₀ ( P 0.05). These results indicate that dietary supplementation of 2% Chlorella powder in the commercial diets could improve growth, feed utilization, serum cholesterol level, and whole-body fat contents in juvenile Japanese flounder.     

Progress in Controlled Breeding of Summer Flounder,Paralichthys dentatus,and Southern Flounder,P. lethostigma

ABSTRACT

The sum mer floun der, Paralichthys dentatus, and the south ern floun der, P. lethostigma, are high value flat fish spe cies and im -por tant can di dates for com mer cial aquaculture in the east ern U.S. Wild-caught adults of both spe cies have been spawned ei ther nat u rally or by hor mone-in duc tion dur ing their first year in cap tiv ity, but spawn ing suc -cess and fre quency of vo li tional spawnings im proves with size/age and ha bit u a tion (>1.5 year) to cap tiv ity. Con trolled-en vi ron ment tanks (2.5-10 m³) sup plied with re cir cu lat ing sea wa ter (32-36 ppt) are used for photo -thermal con di tion ing of broodstock to fa cil i tate en vi ron men tal con trol, ob ser va tion, han dling, and feed ing. Stocking den si ties of 1.7-4.11 kg/m³and sex ra tios of 1-2 males:1 fe male are rec om mended, but op tima have not been de ter mined. In the sum mer floun der, com mer cial hatch er ies use hor mone-in duced spawn ing of photothermally con di tioned fish to sup -ply fingerlings year round. In tra mus cu lar im plan ta tion of a slow-re lease LHRHa pel let (dose ～100 μg/kg) into fe males with max i mum fol li cle diameters >500 μm or with mean oocyte di am e ters rang ing from 258-456 μm in duces re pet i tive ovu la tion and spawn ing. Com mer cial culturists pres ently opt for strip spawn ing, us ing a “light ta ble” to es ti -mate time of ovu la tion, but hor mone-in duced vol un tary spawn ing and nat u ral spawn ing with out hor mone in duc tion could be come more prev a -lent with lon ger-term ac cli ma tion and do mes ti ca tion. In the south ern floun der, im plan ta tion of a slow-re lease LHRHa pel let (～100 μg) has also in duced re pet i tive ovu la tion and spawn ing, al low ing mul ti ple strip spawn ing or vo li tional spawn ing in fe males with max i mum fol li cle di -am e ters > 500 μm. Large num bers of vi a ble em bryos have also been pro -duced through nat u ral spawn ing with out hor mone in duc tion. Through photothermal ma nip u la tion, the nat u ral spawn ing pe riod has been ex -tended by 2-3 months, but ad di tional stud ies are needed to pro duce fingerlings year round. A fun da men tal prob lem in the con trolled re pro -duc tion of both the sum mer floun der and south ern floun der is the vari -abil ity in num ber of eggs and the fer til ity rates among fe males and among con sec u tive spawns from the same fe male. More pre dict able rates of ovu la tion, as well as of fer til iza tion and hatch ing, are needed to lower costs of seed pro duc tion. Vari able spawn ing suc cess can be at trib -uted in large part to in con sis tent male per for mance and in ad e quate spermiation. Hor mone treat ments used to in duce ovu la tion in fe males have been in ef fec tive in in duc ing spermiation in males, and al ter na tive ther a pies are needed. In fe males, egg qual ity may pre sum ably be im -proved by op ti miz ing nutri tions, en vi ron men tal con di tion ing, and hor -mone doses and re lease rates. To date, adult broodstock are ob tained from the wild, and the po ten tial for se lec tive breed ing or for pro duc ing interspecific hy brids re mains un tapped.     

Influence of Dietary Glycyrrhetinic Acid Combined with Different Levels of Lipid on Growth,Body Composition,and Cortisol of Juvenile Channel Catfish,Ictalurus punctatus

Glycyrrhetinic acid (GA), the main active constituent of Glycyrrhiza glabra roots, is extensively used as food additives and herbal medicines. This study was carried out to evaluate the effects of different dietary levels of GA on growth and body composition of channel catfish (average weight, 1.10 ± 0.02 g). Eight diets were formulated to contain two levels of lipid (6.0 and 8.0%), and four levels of GA (0, 0.3, 0.6, and 0.9 g/kg). The experiments lasted for 60 d. Results showed that weight gain tended to decrease as dietary GA levels increased (P > 0.05) with the lowest found in fish fed 0.9 g/kg dietary GA (P < 0.05). Feed intake increased significantly as dietary GA concentrations increased up to 0.6 g/kg (P < 0.05) and viscera/body ratio, condition factor, hepatosomatic index, and intraperitoneal fat ratio decreased significantly as GA concentration increased (P < 0.05). Lipid content of whole body, viscera, and liver decreased significantly (P < 0.01) as dietary GA increased, whereas moisture content showed an opposite trend. The cortisol in fish fed 0.3 and 0.6 g/kg GA was not significantly higher than that of fish without GA supplementation, but glucose in the former two groups was higher (P < 0.05). Results of this study indicate 0.3 and 0.6 g/kg GA had a positive influence in reducing body lipid and IFR deposition in channel catfish without significant side effects on growth. The beneficial effect may be due to extending endogenous cortisol half‐life and increasing the duration of action.     

Optimum Dietary Protein Levels and Protein to Energy Ratios in Olive Flounder Paralichthys olivaceus

The olive flounder Paralichthys olivaceus is one of the most commercially important fish species in Korea. In order to formulate better diets for cultured olive flounder we evaluated the optimum dietary protein requirements for larval, fry and juvenile olive flounder, and the optimum dietary protein to energy ratio for juvenile olive flounder. Results of four separate experiments suggested that the optimum dietary protein requirements were 60% in larvae (0.3 g), 46.4–51.2% in 4.1-g juvenile, and 40–44% in 13.3 g growing olive flounder. The optimum dietary protein to energy ratio based on weight gain, feed efficiency, specific growth rate, and protein retention efficiency was 27–28 mg protein/kJ 2 energy (35 and 45% CP for diets containing 12.5 and 16.7 kJ energylg diet, respectively).