A Dynamic, Stochastic Model of a Land-Based Summer Flounder Paralichthys dentatus Aquaculture Firm

Exploring the possibilities for commercial aquaculture has historically concentrated on reducing production uncertainty by focusing on an animal's biology and the engineering of the production facility. However, the aquaculturist faces both production and market uncertainty, both of which may significantly affect the economic feasibility of a production facility. We developed a dynamic stochastic model to compare alternative production and marketing scenarios and used the net present value of returns to evaluate the scenarios. Based on the model and the scenarios we examined, firms producing summer flounder Paralichthys dentatus are unlikely to be profitable unless they locate near and use a source of salt-water, sell their product predominately to sushi chefs (or other premium market outlets) who desire medium-sized live fish, and engage in strategies that account for market dynamics.     

Effects of Rotifer and Artemia Fatty-Acid Enrichment on Survival, Growth and Pigmentation of Summer Flounder Paralichthys dentatus Larvae

Abstract— Enrichment of live food for marine fish larvae with highly unsaturated fatty acids (HUFA) has been shown to improve survival, growth and stress resistance in many species and to decrease pigmentation abnormalities in flatfish. In order to aid the developing summer flounder industry, we conducted an experiment in which summer flounder larvae were fed diets differing in HUFA composition to determine whether enrichment with a commercially available product would increase survival and growth and reduce the incidence of abnormal pigmentation. We also examined whether growing unenriched rotifers on different species of algae would affect the survival, growth and pigmentation of the flounder larvae to which they were fed. Growth of summer flounder larvae was significantly better when they were fed HUFA-enriched Mtifers and Artemia rather than unenriched and, among the unenriched treatments, was significantly better when the larvae were fed rotifers raised on Isochrysis galbana rather than on Tetraselmis suecica . The percentage of larvae that failed to complete metamorphosis during the experiment was significantly higher in the unenriched treatments than in the enriched treatments. Neither survival nor percentage of individuals with pigmentation abnormalities were significantly different among the treatments.     

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 Water Velocity on Conditioning of Summer Flounder,Paralichthys dentatus,for Net Pens

Abstract

Attempts to rear summer flounder, Paralichthys dentatus, in net pens have suffered from high mortality during the month after fish were transferred from a nursery facility to pens. We investigated whether exposing summer flounder to increased (and constant) current velocity in the nursery stage would condition them for better performance in cages. Three experiments were conducted with different water velocities in tanks, using fish of 124±4 g (exposed to 0, 15, or 30 cm/sec for 60 d), 257±12 g (exposed to 0, 20, or 40 cm/sec for 60 d) and 387±13 g (exposed to 0, 15, or 30 cm/sec for 30 d), in a raceway system with adjustable paddlewheels. For all of the size groups of fish, survival was significantly reduced at the highest current velocity. For both 124-g and 257-g fish, growth in the medium-velocity treatment was significantly better than that in the control (0 cm/sec) treatment, which in turn was better than that in the high-velocity treatment. For 387-g fish, growth at medium velocity was significantly greater than that at high velocity; control fish were lost due to a system malfunction. Food consumption data from the 257-g fish showed that the fish in medium velocity grew most because they consumed significantly more food during the experiment than did fish in the control, which in turn consumed significantly more than fish in high velocity. Similarly, 387-g fish in medium velocity consumed the most food, but the difference was not significant in this case. At the end of the laboratory experiment with 124-g fish, fish from the control and medium-velocity treatments were moved to cages in Narragansett Bay, Rhode Island, where currents of about 1 knot (approx. 55 cm/second) are routine. After three weeks in the cages, no significant differences in survival were observed (control = 83±12%; medium velocity = 81±2%). Subsequent damage to some of the cages and escapement of the fish precluded further statistical analysis of survival, as well as any growth measurements. At the end of the laboratory experiment with 387-g fish, fish from medium- and high-velocity treatments were moved to the cages; however, survival in this case was very low (<10% in all cages), perhaps due to heavy waves from an offshore hurricane. We conclude that current velocities of 15-20 cm/second in the nursery improve growth of juvenile summer flounder, that current velocities of 30-40 cm/second are excessive, but that increased current velocity in the nursery does not improve fish survival upon transfer to cages.     

First Evidence for Hybrid Breakdown in the Backcross of Olive Flounder,Paralichthys olivaceus,and Summer Flounder,Paralichthys dentatus

Hybrid and parental backcross experiments were performed using olive flounder, Paralichthys olivaceus, summer flounder, Paralichthys dentatus, and their female F₁ hybrids to examine hybrid fitness in the backcross. Fertilization rate, hatching rate, and combined fitness measure (CFM, product of fertilization rate and hatching rate) were detected and the results showed that the CFM of hybrid and backcross generations was reduced significantly compared to pure olive flounder crosses. Genomic inheritance from parents to backcross progeny was also detected by amplified fragment length polymorphism (AFLP). Almost all AFLP bands observed in parents were presented in backcross progeny (backcross1, 218/227; backcross2, 265/282), although 9 and 17 parental bands were missing in backcross1 and backcross2, respectively. Novel bands (absent in parents) also occurred in progeny at the frequencies of 5.63% (13/231) in backcross1 and 3.28% (9/274) in backcross2. Additionally, 27.40 and 31.18% of AFLP markers deviated from expected Mendelian ratio in backcross1 and backcross2, respectively. The present study suggests that genetic incompatibilities may exist between olive flounder and summer flounder. Furthermore, possible implications of segregation distortion for reduced hybrid fitness in backcross generations are discussed.     

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.     

Effects of Different Feed Habituation Methods on Survival and Feed Habituation Success of Largemouth Bass,Micropterus salmoides,in a Recirculating Aquaculture System

Demand for food size and trophy largemouth bass, Micropterus salmoides, is steadily increasing. However, largemouth bass, a carnivorous species, are more difficult to feed habituate than other commercially produced fish. Improving current feed habituation techniques to increase the percentage of fingerlings successfully feed habituated would increase profits, productivity and efficiency, and available product in the largemouth bass industry. The focus of this research was to evaluate different combinations of automatic feeders and supplemental hand feeding to determine the feed habituation success under commercial largemouth bass production conditions. Hand feeding, using only automatic feeders, or combinations of both, did not result in significant differences with regard to survival or feed habituation success. Initial fingerling size (total length, TL) was found to be the most important factor affecting survival and feed habituation success. Fish ranging from 40 to 50 mm (TL) survived and feed habituated at significantly higher rates than 30–40 and 50–60 mm (TL) fingerlings. Medium‐sized fish provide the best results in terms of feed habituation success and survival. The results suggest any combination of hand feeding and automatic feeders may be used to achieve feed habituating success in largemouth bass.     

Development of a Squid-hydrolysate-based Larval Diet and its Feeding Performance on Summer Flounder, Paralichthys dentatus, Larvae

Locally generated squid‐processing byproduct was processed into concentrated hydrolysate (22% solids, 17.3% protein, and 3.0% lipid, primarily phospholipids—11.6% eicosapentaenoic acid/24.5% docosahexaenoic acid on a lipid weight basis). Two microparticulate diets (65% protein, 19% lipid, 7.5% carbohydrate, and 19.12 MJ/kg energy, on a dry weight basis) were prepared using squid hydrolysate (SH) and squid‐herring hydrolysate as sole protein sources (73.3 and 78.65% of the whole diet, respectively). A 22‐d feeding trial with summer flounder, Paralichthys dentatus, larvae of 17 d after hatch showed that the survival rate (92%) of larvae fed SH was significantly (P < 0.05) higher than those of larvae fed live Artemia nauplii (81%) and a commercial diet, Proton (65%), while specific growth rates (SGR) were comparable (2.23% /d for SH and 2.86% /d for Artemia) with the lowest for Proton (1.39% /d). After switching from commercial and Artemia diets to a SH diet for 17 d following the 22‐d feeding, significant improvements were seen in survival rates of postweaning larvae fed previously commercial (65.28–76.57%) and Artemia diets (81.25–89.07%).     

不同摄食水平对牙鲆幼鱼生长及能量收支的影响

在水温(20.0±0.5)℃,摄食水平分别为体质量的1.0%、1.5%及饱食条件下,进行牙鲆幼鱼[体质量为(35.08±0.05)g]的生长和能量收支的研究。试验结果表明,随着摄食水平的增加,鱼体干物质、蛋白质和能量表观消化率随摄食水平的增加而增加;湿质量特定生长率随摄食水平的增加呈线性上升,干物质、蛋白质和能量特定生长率呈对数增加;饲料湿质量转化效率不受摄食水平的影响,饲料干物质、蛋白质和能量转化效率随摄食水平的增加先升后降。粪能占摄食能的比例随摄食水平的增加而显著降低,生长能占摄食能的比例随摄食水平的增加先升后降,代谢能占摄食能的比例变化与生长能占摄食能的比例变化相反。各个摄食水平下能量收支式为:1.0%:100.00C=28.99G+2.34F+6.03U+62.64R;1.5%:100.00C=37.19G+1.94F+5.27U+55.60R;饱食:100.00C=30.73G+1.36F+5.16U+62.75R。     

Effect of Different Dietary Protein and Lipid Levels on Growth Performance and Body Composition of Juvenile Southern Flounder,Paralichthys lethostigma,Reared in a Recirculating Aquaculture System

The effects of six formulated diets containing different protein and lipid levels on growth performance and body composition of juvenile southern flounder were evaluated. Test diets were prepared with a combination of three crude protein (CP) levels (45, 50 and 55%) and two crude lipid (CL) levels (10 and 15%). Diets (CP/CL) were as follows: 45/10, 45/15, 50/10, 50/15, 55/10, 55/15 and a commercial diet (50/15). Southern flounder (1.10 g) were fed the respective diets for 42 d in triplicate recirculating tanks (20 fish/tank). Percent body weight gain (BWG) for fish fed diet 45/10 (413%) and the commercial diet (426%) were significantly (P < 0.05) lower than fish fed other diets (823–837%). Increasing protein level from 45 to 50% produced a significant increase in BWG for the 10% lipid diet (823%) but further increasing protein did not produce a significant effect on BWG irrespective of dietary lipid levels. Specific growth rate (SGR), feed intake, feed conversion efficiency (FCE), protein efficiency ratio (PER), and total lipid content in the whole body were significantly affected by different dietary protein and lipid levels. Results indicated that a combination of 50% protein and 10% lipid was optimal for the growth performance of southern flounder juveniles.     

盐度对漠斑牙鲆幼鱼存活、生长及摄食的影响

盐度对漠斑牙鲆幼鱼的存活的影响较小,将漠斑牙鲆幼鱼从盐度为32的海水直接放入盐度为24、16、8、0的水中观察48 h存活情况,仅盐度0组成活率为75%,其他盐度组均为100%.在盐度为32、24、16、8、0各试验组中,经1个月饲养,生长速度和饵料系数均无显著差异.盐度越低越有利于漠斑牙鲆白化个体康复正常体色.     

Effects of Larval Stocking Density on Laboratory-Scale and Commercial-Scale Production of Summer Flounder Paraliehthys dentatus

Abstract.— Three experiments investigating larval stocking densities of summer flounder from hatch to metamorphosis, Paralichthvs dentalus, were conducted at laboratory‐scale (75‐L aquaria) and at commercial scale (1,000‐L tanks). Experiments 1 and 2 at commercial scale tested the densities of 10 and 60 larvae/L, and 10, 20, and 30/L, respectively. The laboratory scale experiment tested the densities of 10, 20, 30, and 40 larvae/L. Experiments were carried out in two separate filtered, flow‐through seawater systems at URI Narragansett Bay Campus (laboratory‐scale), and at GreatBay Aquafarms, Inc. (commercial‐scale). At both locations, the larvae were raised in a “greenwater” culture environment, and fed rotifers and brine shrimp nauplii according to feeding regimes established for each location. Water temperature was maintained at 21C (± 2) and 19C (± 1) for the duration of laboratory and commercial experiments, respectively. Experiments 1 and 2 at the commercial location were terminated at 42 and 37 d post hatch (dph), respectively, and the laboratory experiment lasted 34 DPH. Larvae initially stocked at 10/L grew to an average length of 14.3 and 14.4 mm, and were significantly larger (P < 0.05) than those stocked at 30/L (13.1 mm) and 60/L (11.7 mm) in commercial scale experiments I and 2, respectively. At laboratory scale, no significant differences in length were detected, although mean total length tended to decrease with increasing stocking density (average length of 14.2, 13.3, 12.7, and 12.7 mm for treatments of 10, 20, 30, and 40/L, respectively). Final survival percentage was not affected by stocking density in either commercial experiment, and was 61 and 40% for treatments of 10 and 60/L in Experiment 1, respectively, and 62, 59, and 56% for Experiment 2, respectively. Similarly, there was no significant difference in final survival percentage among treatments in the laboratory experiment, which averaged 59, 55, 56, and 37% for treatments of 10, 20, 30, and 40L. respectively. Since larval length was not different between the intermediate densities (20 and 30 Iarvae/L), and because high‐density rearing can produce a much greater numerical yield per tank, we recommend a density of 30 larvaen as an optimal stocking density for the hatchery production of summer flounder.     

Growth, Survival, and Feed Conversion Rates of Hatchery-Reared Mutton Snapper Lutjanus analis Cultured in Floating Net Cages

Abstract.— The aquaculture performance of mutton snapper Lutjanus analis raised in floating net cages was assessed by measuring their growth, survival, and feed conversion rates during a growout trial conducted in a 3.2‐ha saltwater lake in the Florida Keys, Florida, USA. Approximately 10,500 hatchery‐reared finger‐lings were stocked in two circular, high‐density polyethylene (HDPE) net cages of 7‐m diameter × 7‐m deep (300 m²) and 10‐m diameter × 7‐m deep (600 m³) dimensions. Cages were stocked at 25 fish/m³ (3.2 kg/m³) and 5 fish/m³ (0.72 kg/m³), respectively. Fish grew from a mean of 16.5 g to 302.8 g (25.6 cm TL) in 246 days in the former cage and from a mean of 42.3 g to 245.6 g (23.8 cm TL) in 178 d in the latter cage. Growth rates in weight were best expressed by the following exponential equations: cage 1 (high stocking density): W = 20.716 e^0.0112x (r²= 0.83); cage 2 (low stocking density): W = 38.848 e^0.0118x (r²= 0.81). Length‐weight data indicate that hatcheryraised, cage‐cultured mutton snapper are heavier per unit length than their wild counterparts. There was no significant difference (P < 0.05) between the slopes of the two lines, indicating that fish in the two cages grew at the same rate. The length‐weight relationships for mutton snapper stocked in cages 1 and 2 are expressed, respectively, by the equations W = 0.000009 L ^3.11 (r²= 0.99) and W = 0.000005 L ^3.22 (r²= 0.97). Overall feed conversion rate for both cages combined was 1.4. Approximately 10% of the fish sampled exhibited some degree of deformity, particularly scoliosis. Overall survival rate was 70%. Results suggest that L. analis has potential for aquaculture development in net cage systems.     

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.     

Optimum Dietary Level of Chlorella Powder as a Feed Additive for Growth Performance of Juvenile Olive Flounder,Paralichthys olivaceus

ABSTRACT

The present study was conducted toestimate the optimum dietary supplementation level of Chlorella powder as a feed additive to optimize growth of juvenile olive flounder, Paralichthys olivaceus. Four experimental diets supplemented with Chlorella powder (CHP) at 0, 1, 2 and 4% (CHP₀, CHP₁, CHP₂, and CHP₄, respectively) of diet as a dry-matter (DM) basis were prepared. Three replicate groups of fish averaging 1.1±0.02 g were fed one of the four experimental diets for 12 weeks. After the feeding trial, fish fed the CHP₂ diet had a higher (P < 0.05) weight gain (819%) than did fish fed CHP₀ (707%) and CHP₁(712%); however, there was no significant difference between fish fed CHP₂ (8197%) and CHP₄ (7559%) as among fish fed CHP₀, CHP₁, and CHP₄ (P > 0.05). Fish fed CHP₂ had a higher (P < 0.05) feed efficiency (134%) than did fish fed CHP₀ (123%); however, there was no significant difference (P > 0.05) among fish fed CHP₀ (123%), CHP₁ (125%), and CHP₄ (125%) as among fish fed CHP1 (125%), CHP₂ (134%), and CHP₄ (125%). Fish fed CHP₂ and CHP₄ had a lower (P < 0.05) serum glucose level (average 32.9 mg/dL) than did fish fed CHP₀ and CHP1 (average 34.8 mg/dL). Fish fed CHP1 and CHP₂ had a lower (P < 0.05) serum glutamic oxaloacetic transaminase (GOT) level than did fish fed CHP0 and CHP₄. Glutamic pyruvic transaminase (GPT) levels significantly (P < 0.05) deceased as dietary CHP increased. Fish fed CHP₂ and CHP₄ had a less (P < 0.05) whole-body fat than did fish fed CHP₀. These results indicate that the optimum dietary supplementation level of Chlorella powder as a feed additive in juvenile olive flounder could be approximately 2% of diet.     

Evaluation of Tilapia Effluent with Ion Supplementation for Marine Shrimp Production in a Recirculating Aquaculture System

Reuse of fish effluent for the culture of marine shrimp, such as Pacific white shrimp, Litopenaeus vannamei, could provide an opportunity for the US shrimp farming industry to ease constraints (e.g., environmental concerns and high production costs) that have limited them in the past. In this study under laboratory‐scale conditions, the feasibility of culturing L. vannamei in effluents derived from a commercial facility raising tilapia in recirculating aquaculture systems (RAS), supplemented with various salt combinations, was compared to the shrimp’s survival and growth in well water supplemented with 17.6 (control) and 0.6 (freshwater treatment) g/L synthetic sea salt. Three independent trials were conducted in RAS in which survival and growth in the control, the freshwater treatment, and two effluent treatments were compared. Water quality during this study was within safe levels and no differences (P < 0.05) between treatments were observed for dissolved oxygen, nitrite, pH, total ammonia nitrogen, and temperature. However, average nitrate and orthophosphate levels were consistently more than an order of magnitude greater in the effluent treatments compared to the control and the freshwater treatments. Survival and growth of shrimp over 6‐wk periods did not vary significantly between the control and the freshwater treatments; however, shrimp tested in the tilapia effluents often exhibited significant effects (P < 0.05) depending on the salts added. In the low‐salinity waters, correlations (P < 0.05) were observed between Ca²⁺, Mg²⁺, Ca²⁺ and Mg²⁺, K⁺, Na⁺ : K⁺ and Ca²⁺ : K⁺, and shrimp survival and growth. The results of this study revealed that L. vannamei can be raised in tilapia effluent when supplemented with synthetic sea salt (0.6 g/L), CaO (50 mg/L Ca²⁺), and MgSO₄ (30 mg/L Mg²⁺).     

Partial Replacement of Fish Meal with Plant Protein Sources Singly and in Combination in Diets for Summer Flounder,Paralichthys dentatus

Soybean meal (SBM), corn gluten meal (CGM), and canola protein concentrate (CPC) as alternative protein sources to fish meal (FM) were individually evaluated for growth performance at 0, 20, 30, 40, and 50% replacement with amino acid (AA) supplementation using juvenile summer flounder, Paralichthys dentatus, in an 8‐wk feeding. Two‐way ANOVA indicated no significant main effect for plant protein source, but a significant main effect for replacement level. Comparison of the individual treatments revealed significant differences in weight gain (WG) between the FM treatment and 50% replacement level for all protein sources, as well as between the FM treatment and 30% replacement with CPC. Replacement of FM with SBM at 40% resulted in the least cost/kg WG. In a follow‐up study, a combination of SBM–CGM–CPC at 40% replacement was evaluated with and without AA, phytase (0.2%), or taurine (1%), versus FM and SBM (40% replacement of FM) with AA. The SBM–CGM–CPC diet with either AA or taurine provided a significantly better food conversion ratio and less cost/kg WG than the SBM diet, and the SBM–CGM–CPC diet with taurine provided a significantly better protein efficiency ratio than the SBM diet. On the basis of these results, more study of taurine in plant protein diets for summer flounder appears warranted.     

循环水养殖赤点石斑鱼幼鱼放养密度研究

将体质量(10.82±0.17)g的赤点石斑鱼(Epinephelus akaara)幼鱼饲养在室内循环水、直径40cm×水深50cm池中,每个池中10(G_(10))、20(G_(20))和40(G_(40))尾,投喂常规饲料,每周测4次水质。8周的养殖结果表明,养殖时间和放养密度均影响赤点石斑鱼的生长、存活和水质。随着养殖时间的加长,成活率逐步降低,但整体保持在40.00%~90.00%之间,G_(10)组的成活率显著高于G_(40)组(P0.05)。试验结束时,赤点石斑鱼的增重率(WGR)变化在(47.97±1.98)~(68.02±2.34)%之间,特定生长率(SGR)变化在(0.70±0.33)~(0.93±0.42)%/d之间,两指标不同密度组差异显著(P0.05),而各组鱼的肝体比(HIS)、内脏比(VSI)和肥满度(CF)差异不显著(P0.05)。     

Effects of Feed Application Rates on Growth, Survival, and Feed Conversion of Juvenile Snakehead Channa striatus

Growth, survival and feed conversion ratio of juvenile snakehead Channa striatus were evaluated when fed a dry, formulated feed (50% crude protein) at 24 ± 1 C. Six daily feed application rates were used (0%, 5%, 10%, 15%, 20%, and 30%), as a percentage of fish body weight, with three replicates per treatment. After 29 d, final weights were all significantly greater ( P < 0.01) than initial weights, except for the 0% application. Feed applications higher than 5% did not result in increased growth ( P > 0.05). Feed conversion ratio was 0.99 at 5% feed application, and 6.3 at 30% feed application. Fish survival was increased by providing formulated diet, but no further improvement was found when feed applications exceeded 5%. Cannibalism was reduced by providing formulated feed, but it was unavoidable when substantial differences in fish size existed, even when feeding ad libitum . Our results indicate that the optimal feed application rate is close to 5% body weight/d for juvenile snakehead.