Delivering oxytetracycline to first-feeding zebrafish, Danio rerio (Hamilton), and goby, Asterropteryx semipunctata Rüppell, larvae using lipid spray beads

Lipid spray beads (LSB) were evaluated for delivery of the low-molecular weight, water-soluble antibiotic, oxytetracycline·HCl (OTC) to fish larvae. Various OTC core-to-lipid ratios and OTC core concentrations were evaluated to maximize OTC delivery efficiency by LSB. Acceptability and digestion of LSB containing OTC and riboflavin by larval zebrafish, Danio rerio (Hamilton), and larval gobies, Asterropteryx semipunctata Rüppell, were also evaluated. Increasing LSB core-to-lipid ratios from 1:3 to 1:1 v/v resulted in an increase in encapsulation efficiency (EE) from 2.33 to 3.68% w/w. Increasing OTC concentrations of core solutions from 0.1 to 0.5 g OTC mL⁻¹ increased EE from 3.95 to 18.77% w/w, respectively. Although retention efficiency (RE) was unaffected by this increase, delivery efficiency was increased to 7.9 ± 0.7% w/w, after correcting for leakage losses because of the suspension of beads in water for 60 min. Consumption of LSB containing OTC by first-feeding zebrafish and goby larvae was confirmed by analysis of feeding incidence and gut fullness. Visual observations of larvae fed on LSB containing riboflavin indicated that larvae of both species digested LSB. Zebrafish larvae fed on OTC LSB contained 39.3 ± 2.5 ng OTC after purging LSB from their guts. Use of LSB provides an effective means of delivering therapeutics to fish larvae and could greatly reduce required doses compared with current methods of immersing larvae in solutions of therapeutic agents.     

珠江肇庆江段赤眼鳟开口后仔、稚鱼的异速生长分析

运用实验生态学的方法,对珠江肇庆江段的赤眼鳟(Spualiobarbus curriculus)开口后仔稚鱼的异速生长及其生态学意义进行研究.结果表明,赤眼鳟开口后仔鱼的游泳、感觉和摄食器官快速分化,许多器官的发育存在异速生长:身体各部分中,头长、尾长和头高为正异速生长,腹长在开口后至20日龄为负异速生长,20日龄后为正异速生长;体高也存在正异速生长,但生长拐点(18日龄)前后均为正异速生长.在头部器官中均存在异速生长拐点,吻长、眼径和眼后头长的生长拐点分别是开口后23、19和16日龄.运动器官中,背鳍、腹鳍、臀鳍及尾鳍均存在异速生长,且分别在开口后18、19、17和14日龄达到生长拐点.游泳、感觉及摄食相关的器官的优先发育,使开口后的仔鱼在最短的时间内获得了与早期生存密切相关的各种能力,对适应复杂多变的外界环境具有重要的生态学意义.     

不同温度、饵料对兴凯湖翘嘴鱼白仔鱼摄食和生长的影响

本研究了温度和饵料对兴凯湖翘嘴鲌仔鱼的摄食和生长的影响。结果表明：兴凯湖翘嘴鲌仔鱼在不同温度下的生长速度和成活率存在着较大差异，在水温为25℃时仔鱼生长速度最快、成活率最高，18℃时仔鱼生长速度最慢、成活率最低；投喂不同的饵料对兴凯湖翘嘴鲌仔鱼的生长速度和成活率也有较大差异，投喂浮游动物的仔鱼生长速度最快、成活率最高，投喂蛋黄和开口料的仔鱼生长速度最慢、成活率最低。水温为25℃、23℃、20℃、18℃时，仔鱼的瞬时生长率分别为4．09％、2．05％、1．12％、1．08％；仔鱼的日平均成活率分别为90．96％、82．89％、81．78％、74．67％。对兴凯湖翘嘴鲌仔鱼投喂浮游动物、混合料、开口料、蛋黄，其瞬时生长率分别为3．34％、2．42％、1．45％、1．40％；仔鱼日平均成活率分别为95．89％、92．22％、81．11％、83．89％。     

Effects of protein and lipid sources on the growth and survival of red sea bream Pagrus major and Japanese flounder Paralichthys olivaceus receiving micro-bound diets during larval and early juvenile stage

The effects of dietary protein and lipid sources on growth and survival of the red sea bream Pagrus major (30‐days old) and Japanese flounder Paralichthys olivaceus (15‐days old) were examined using four zein‐microbound diets (MBD) containing the following nitrogen and lipid sources: MBD‐1, SBP‐1000 (soybean peptides with molecular weights of about 1000) + fish oil calcium soap (FOCS); MBD‐2, SBP‐3000 (molecular weights of about 3000) + FOCS; MBD‐3, soybean protein isolate (SPI) + FOCS; MBD‐4, SBP‐1000 + stearoyl calcium lactate (SCL). Six groups of the test fish were maintained on the following diets for 30 days; group 1, live food; group 2, 1/2 live food + 1/2 MBD‐1; group 3, MBD‐1; group 4, MBD‐2; group 5, MBD‐3; group 6, MBD‐4. In the red sea bream, high performance in terms of total length (TL) and body weight gain (BWG) was obtained in groups 1, 2, 3 and 4. However, the fish receiving MBD‐3 (group 5) and MBD‐4 (group 6) had shorter TL and lower BWG than those receiving the other diets. Regarding the Japanese flounder, high performance in terms of TL, BWG, and survival rate (SR) was obtained in groups 1 and 2. Group 3 receiving MBD‐1 gave the BWG and SR close to those of group 2 but lower than group 1. In contrast, groups 5 and 6 receiving MBD‐3 or MBD‐4 alone had significantly (P < 0.05) shorter TL and lower BWG than groups 1 and 2. The present study thus indicated that soybean peptides with molecular weights of 1000–3000 and FOCS are superior to SPI and SCL as nitrogen and lipid sources of MBD for the red sea bream and Japanese flounder at larval and early juvenile stage.     

Application of microparticle diets for Japanese flounder Paralichthys olivaceus larvae

ABSTRACT:   A feeding trial was conducted with two newly developed microparticle diets (MD-Q and MD-V), which differed in the mixing ratios of two types of casein hydrolysates (C700 and C800) as the protein source. The ratio of C700 and C800 were adjusted to 7:3 in MD-Q and 6:4 in MD-V, respectively. Japanese flounder larvae were fed from 7 days after hatching (d.a.h.) to 32 d.a.h. on live food (LF), MD solely, MD + 1/3 LF (either of the MD and one-third quantity of the live food) and 1/3 LF (one-third quantity of live food alone), respectively. They were then switched to Kyowa diet B from 33 d.a.h. until 40 d.a.h. The larvae fed on MD-Q exclusively had a higher survival rate (36.4%) than those fed on MD-V (24.2%) by 22 d.a.h. Unfed larvae could survive up to only 12 d.a.h. Larvae fed on MD-Q + 1/3 LF also had a significantly higher survival rate (34.2%) than those on MD-V + 1/3 LF (16.3%) and 1/3 LF solely (15.4%) at 32 d.a.h. These results suggest the potential of MD-Q as a part replacement for LF from the early developmental stage in the seed production of Japanese flounder.     

Effect of prey type and size on the growth,survival and pigmentation of cod (Gadus morhua L.) larvae

The aim of this study was to investigate the effect of natural zooplankton versus rotifers and the effect of prey size on the growth and survival of cod larvae. At 20 days post hatch (DPH) myotome height, standard length and dry mass were significantly higher in larvae fed zooplankton compared to those fed rotifers. The dry mass at age 25 DPH was 135 μg (±45), 331 μg (±114), 391 μg (±121) for larvae fed rotifers, small size and large size plankton, respectively. At 25 days post hatch, the survival rates were 41.8% (±10.5), 90.7% (±2.3) and 91.4% (±1.7) for larvae reared on rotifers, small size and large size plankton, respectively. The limited growth and survival of cod larvae reared on rotifers were not mainly caused by the small size of rotifers. Large differences in skin coloration between larvae in the rotifer group and the two zooplankton groups were observed, probably caused by the large difference in astaxanthin levels in rotifers and natural zooplankton. We suggest that the nutritional composition of rotifers is a limiting factor for cod larvae growth and survival.     

Molecular identification of laser‐dissected gut contents from hatchery‐reared larval cod,Gadus morhua: a new approach to diet analysis

The transition between endogenous and exogenous feeding in hatchery production of fish larvae has long been a bottleneck to increased production. Identification of alternative prey species with a wider array of nutritional profiles is essential for further expansion and diversification within the aquaculture industry. Traditional morphological methods to identify dietary composition are limited. In this study, we present a novel DNA‐based methodology for identifying the gut contents of larval fish that is independent of prey retaining identifiable characteristics. Laser capture microdissection is used to collect ingested material for DNA extraction, thus limiting contaminating DNA originating from the larval fish. PCR is then conducted using universal eukaryotic primers that have the potential to detect a wide diversity of prey items. Using this approach, we identified ingested Artemia salina from hatchery‐reared Gadus morhua larvae. Differential length amplification PCR was used to evaluate the effects of DNA degradation on the sensitivity of A. salina detection. Although it was possible to detect A. salina with relatively long (626 bp) fragments, targeting smaller fragments (264 bp) resulted in the highest return of prey sequences. This combined LCM and molecular approach to diet analysis could offer a more complete assessment of the diets of naturally feeding larvae.     

The response of fish larvae to decadal changes in environmental forcing factors off the Oregon coast

We conducted a statistical analysis to characterize the influence of large‐scale and local environmental factors on presence‐absence, concentration, and assemblage structure of larval fish within the northern California Current (NCC) ecosystem, based on samples collected at two nearshore stations along the Newport Hydrographic line off the central Oregon coast. Data from 1996 to 2005 were compared with historical data from the 1970s and 1980s to evaluate pseudo‐decadal, annual, and seasonal variability. Our results indicate that the most abundant taxa from 1996 to 2005 differ from those of earlier decades. Concentrations of the dominant taxa and total larvae were generally greater in the winter/spring than summer/fall season. Using generalized additive modeling, variations in presence‐absence and concentration of taxa were compared to climate indices such as the Pacific Decadal Oscillation, Northern Oscillation Index, and the multivariate ENSO index and local environmental factors, such as upwelling, Ekman transport, and wind stress curl. Significant relationships were found for various combinations of environmental variables with lag periods ranging from 0 to 7 months. We found that the large‐scale climate indices explained more of the variance in larval fish concentration and diversity than did the more local factors. Our results indicate that readily available oceanographic and climate indices can explain variations in the dominant ichthyoplankton taxa in the NCC. However, variation in response among taxa to the environmental metrics suggests additional unknown factors not included in the analysis likely contributed to the observed distribution patterns and larval fish community structure in the NCC.     

Abundance, depth distribution, diet composition and growth of perch (Perca fluviatilis) and burbot (Lota lota) larvae and juveniles in the pelagic zone of Lake Constance

Abstract— Surveys of larval and juvenile fish in the pelagic zone were made in Lake Constance between April and July 1994 with a plankton net. Perch ( Perca fluviatilis ) and burbot ( Lota lota ) were caught persistently, while other species were found only occasionally. Perch and burbot coexisted in the pelagic zone; both species were found first in mid-May, reached peak density in June, and disappeared from the pelagic zone in late July. However, the abundance of perch was much higher than that of burbot. Perch were distributed mainly near the surface, whereas burbot were more abundant at the deeper strata of 5 and 10 m, exhibiting habitat segregation. Perch fed mainly on copepods and positively selected them during their first month of life, and afterwards, they consumed principally on Daphnia , while burbot fed mainly on copepods and positively selected them throughout the study period. Perch grew significantly faster than burbot, and the mean lengths of perch were about 3 times greater than that of burbot in July. The results demonstrate that perch and burbot were the main species of pelagic larvae in Lake Constance between May and July, and that the two species differed somewhat in depth distribution, diet composition and growth.