Bacterial Interactions in Early Life Stages of Marine Cold Water Fish

Abstract The intensive rearing of various fish species in aquaculture has revealed intimate relationships between fish and bacteria that eventually may affect establishment of a ``normal' mucosal microflora or result in disease epizootics. Interactions between bacteria and mucosal surfaces play important roles both at the egg and larval stages of marine fish. Bacterial adhesion and colonization of the egg surface occur within hours after fertilization. The diverse flora which eventually develops on the egg appears to reflect the bacterial composition and load of the ambient water, but species-specific adhesion at the egg surface may also play a role in development of the egg epiflora. Proteolytic enzymes produced by members of the adherent epiflora may cause serious damage to the developing egg and may also affect further adhesion of the epiflora. Ingestion of bacteria at the yolk sac stage results in establishment of a primary intestinal microflora which seems to persist beyond first feeding. Establishment of a gut microflora is likely to undergo several stages, resulting in an ``adult' microflora weeks to months after first feeding. Ingested bacteria may serve as an exogenous supply of nutrients or essential factors at an early life stage. Early exposure to high bacterial densities is probably important for immune tolerance, and thus for the establishment of a protective intestinal microflora. Successful rearing of early life stages of several marine fish species depends on knowledge of the complex interactions among the cultured organisms and the bacterial communities which develop at the mucosal surfaces and in the ambient water and rearing systems. The routine use of antibiotics during rearing of fish larvae is not advisable, since it may increase the risk of promoting antibiotic resistance and adversely affect the indigenous microflora of the larvae. The use of probiotics has proven advantageous in domestic animal production, and the search for effective probiotics may have a great potential in aquaculture of marine organisms. Bacteria with antagonistic effects against fish pathogens have been successfully administered to several fish species, resulting in decreased mortality or increased growth rate. Received: 14 December 1998; Accepted: 7 April 1999     

Rotifers as food in aquaculture

The rotifer Brachionus plicatilis (O.F. Muller) can be mass cultivated in large quantities and is an important live feed in aquaculture. This rotifer is commonly offered to larvae during the first 7–30 days of exogenous feeding. Variation in prey density affects larval fish feeding rates, rations, activity, evacuation time, growth rates and growth efficiencies. B. plicatilis can be supplied at the food concentrations required for meeting larval metabolic demands and yielding high survival rates. Live food may enhance the digestive processes of larval predators. A large range of genetically distinct B. plicatilis strains with a wide range of body size permit larval rearing of many fish species. Larvae are first fed on a small strain of rotifers, and as larvae increase in size, a larger strain of rotifers is introduced. Rotifers are regarded as living food capsules for transferring nutrients to fish larvae. These nutrients include highly unsaturated fatty acids (mainly 20: 5 n–3 and 22: 6 n–3) essential for survival of marine fish larvae. In addition, rotifers treated with antibiotics may promote higher survival rates. The possibility of preserving live rotifers at low temperatures or through their resting eggs has been investigated.     

Comparison of the Growth and Survival of Larval Turbot in the Absence of Culturable Bacteria with Those in the Presence of Vibrio anguillarum, Vibrio alginolyticus, or a Marine Aeromonas sp

Larval turbot (Scophthalmus maximus) were reared on rotifers (Brachionus plicatilis) in the absence of culturable bacteria for up to 14 days and exhibited growth and high rates of survival (>55% in five experiments). Low numbers of known bacteria were introduced into similar cultures by exposure of the rotifers to a suspension of bacteria prior to addition of rotifers to the larval cultures; Vibrio anguillarum 91079 caused a highly significant decrease (P <0.01) in the proportion of survivors in two separate trials. With an Aeromonas sp. previously isolated from a healthy batch of copepod-fed larvae, there was no significant difference in survival compared with control larvae, even though the density of bacteria in the water of larval cultures reached 10(sup7) ml(sup-1). Bacteria colonized the gut of larvae exposed to Aeromonas-treated rotifers to levels similar to those in conventionally reared fish (>4 x 10(sup4) CFU per larva). Rearing of larvae in the presence of known bacteria provides a means of investigating the interaction of specific bacteria with turbot larvae and could provide a method for the selection of bacteria which may restrict the growth of opportunistic pathogens which would be harmful to turbot larvae.     

Characterization of the bacterial flora of mass cultivated Brachionus plicatilis

Bacterial density and composition in association of mass cultivated rotifers (Brachionus plicatilis, SINTEF-strain) was investigated, during experimental conditions identical to the procedures used for preparing rotifers as live food for marine cold water fish larvae. These procedures include cultivation, enrichment with squid meal and acclimation to low temperature by storage of the rotifer culture at 6 °C. Large variations were observed in the number of rotifer associated (1.8–7.6 · 10³ colony forming units per rotifer^–1) and free-living (0.6–25 10⁷ cells·ml^–1) bacteria. An increase of 50–150% in the bacterial number was normally observed after feeding the rotifer with squid meal, but after three days of acclimation at 6 °C, the bacterial numbers decreased to the initial level.After enrichment of the cultures with squid meal, the similarity in the composition of the bacterial flora between the rotifers and water was reduced. However, acclimation of the culture at 6 °C resulted in better agreement of the rotifer associated flora and that in water. Enrichment of the cultures induced a shift in the bacterial composition from Cytophaga/Flavobacterium dominance to Pseudomonas/Alcaligenes dominance. The bacterial flora of the rotifer cultures are dominated by presumably opportunistic species after enrichment, which may have detrimental effects when rotifers are fed as live food to marine fish larvae.     

The intestinal microflora of farmed Dover sole (Solea solea) at different stages of fish development

The bacterial flora in the intestines of farmed Dover sole ( Solea solea L.) was investigated at different stages of fish development in relation to different diets fed under farming conditions. The flora of water and diets were also analyzed. The dominant generic group isolated from all water samples examined was Pseudomonas Gp IV/ Alcaligenes. The same generic group was dominant in homogenized pelagic larvae indicating a relationship between the microflora of those young fish and that of tank water. In older fish a steady increase in the percentage incidence of Vibrio / anaerogenic Aeromonas was observed in the intestines as fish grew and diets changed. The Vibrio /anaerogenic Aeromonas group was dominant in Lumbricillus rivalis used as an intermediate diet and the increased incidence of this group in fish intestines occurred after fish were fed this diet. The composite pellet used for ongrowing carried a high percentage of Gram positive micro-organisms and there was no relationship between the pellet microflora and that found in the fish intestines.     

A comparison of gut evacuation models for larval mackerel (Scomber scombrus) using serial photography

A novel technique is described, using serial photography of the gut contents of transparent living larval fishes, to generate individual gut evacuation time series. This technique was applied to Atlantic mackerel Scomber scombrus larvae to compare three widely used models of gut evacuation: linear, exponential and square-root. Regression r ² for the exponential model exceeded those for the linear and square root models in 20 of 21 time series, strongly supporting the exponential model. At the initial gut fullness for each time series, total gut evacuation rates calculated with the exponential model averaged 2·2 and 1·3 times greater than those calculated with the linear and square-root models, respectively, and would produce correspondingly higher estimates of feeding rates for field-collected larvae with similar levels of gut fullness. The results highlight the importance of choosing the appropriate evacuation model in feeding studies, particularly those intended to examine short-term changes in larval fish feeding rates, a contributing factor to the highly variable yearly recruitment of many marine fish species.     

Vibrio splendidus biotype 1 as a cause of mortalities in hatchery-reared larval turbot, Scophthalmus maximus (L.)

AIMS: To characterize bacteria associated with turbot larvae feeding on Artemia and identify pathogens causing mortalities in larvae. METHODS AND RESULTS: To identify bacteria associated with mortalities in larval turbot rearing, bacteria were isolated from homogenates of Artemia or from several batches of well-performing or poorly performing turbot larvae. Samples were plated onto marine agar and were characterized using biochemical tests and BIOLOG GN plates. Total culturable aerobic bacteria ranged from 1.9 x 10(5) to 1.8 x 10(6) CFU per larva and >96% of bacteria identified were vibrios. Almost all bacteria were haemolytic and clustered into two phenons represented by Vibrio alginolyticus and Vibrio splendidus. The bacterial flora of Artemia was almost entirely V. alginolyticus, whereas V. splendidus biotype 1 dominated the larval turbot gut flora (69/115 isolates in seven experiments) and formed four different groups based on BIOLOG GN reactions. Of 16 isolates tested for virulence towards turbot larvae, four of the 11 V. splendidus biotype 1 isolates were lethal and all belonged to the same group of V. splendidus biotype 1 isolates. CONCLUSIONS: In a commercial turbot hatchery, the microbial flora of the larval gut was dominated by V. splendidus biotype 1. Four of the 11 V. splendidus biotype 1 isolates caused mortalities in larval turbot and all belonged to one group of the biotype 1 strains identified. SIGNIFICANCE AND IMPACT OF THE STUDY: Identification of four isolates of V. splendidus that are pathogenic for turbot larvae from three separate batches of larval turbot will allow these to be compared with avirulent isolates to define how V. splendidus causes mortalities in larval turbot.     

Cold stress-induced changes in the aerobic heterotrophic gastrointestinal tract bacterial flora of red hybrid tilapia

Fifteen juvenile red hybrid tilapia Oreochromis mossambicus × O. macrochir averaging 50 g body weight were cold-stressed by immersion in 18° C sea water; control fish ( n = 15) were kept at the acclimation temperature of 26° C. Three fish from each group were killed 0, 24, 48 and 72 h after the start of the experiment. Gastrointestinal tracts were removed and dissected into the stomach, anterior gut and posterior gut regions. Aerobic heterotrophic bacteria were identified and enumerated relative to temperature, exposure time and gastrointestinal tract region. Gram negative genera included Alcaligenes, Flavobacterium, Photobacterium, Pseudomonas and Vibrio ; the latter three were predominant. Mean bacterial numbers and taxonomic composition of the microflora varied significantly ( P <0·05) in response to the three test variables. There were greater mean total bacterial numbers at 18 than at 26° C, due primarily to proliferation of Vibrio spp. Mean bacterial numbers after 24 h were greater than those at both the earlier and later sampling periods. Mean bacterial numbers in the stomach were less than those in the anterior and posterior gut, which were not significantly different. The relative abundance of Vibrio spp. was negatively correlated with that of Flavobacterium , which may have reflected competition between pathogenic and nonpathogenic species. Such stress-induced changes in the bacterial microflora may contribute to the onset of disease because several species of Vibrio are known primary or opportunistic fish pathogens.     

Effects of bacterial treatment at early stages of Atlantic cod (Gadus morhua L.) on larval survival and development

Aims: To assess the effects of bacterial treatment at the earliest stages of cod rearing on the microbial load, larval development and performance, testing three bacterial strains (Carnobacterium divergens V41, Arthrobacter sp. and Enterococcus sp.) in vivo that were previously shown to have inhibitory potential towards fish pathogens in vitro. Methods and Results: A bacterial mixture was added eight times to the rearing water from the prehatch to the mid‐larval stage (a 38‐day period). Microbiological analysis of ova, larvae and rearing water was performed regularly. Larval performance and development were evaluated by survival rate, hypersalinity tolerance and physiological measurements. Different larval survival rates were observed within and between treatments, and possibly explained by variations in larval microflora and established probionts. Larvae from one silo, which had been bathed in the bacterial suspension, showed the highest survival rate (42·1%), lowest Vibrio levels, and were significantly heavier (19·3%) and more stress tolerant than control larvae (P < 0·01). This coincided with the intestinal establishment of two of the tested bacteria. Conclusions: Arthrobacter and Enterococcus strains added regularly to the rearing water from the postfertilized egg stage can become established in larval gastrointestinal tract. The Enterococcus strain was associated with increased larval growth, performance and microflora control, indicating its probiotic nature. Significance and Impact of the Study: Regular application of autochthonous probionts may promote larval welfare, development and stress tolerance at early stages, hence increasing production yield in intensive cod larviculture.     

Determination of bacteria associated with reared turbot (Scophthalmus maximus) larvae

In order to extend our knowledge of the presence of bacteria in hatcheries and their influence on rearing performance, the aerobic and facultative bacterial flora associated with farmed turbot larvae were studied in relation to the microflora of the water and diets. A settlement of specific groups of bacterial populations was found in the gut of the larvae. A clear succession of bacterial phenotypes was also observed from day 1 to day 90 post-hatching. Oxidative Gram-negative rods were predominant at the initial stages, whereas some phenotypes of Vibrio were frequent at the final stages. A high heterogeneity of Vibrio species was observed in the intermediate period when the highest mortalities of turbot larvae occur.     

Bacterial Colonization of Cod (Gadus morhua L.) and Halibut (Hippoglossus hippoglossus) Eggs in Marine Aquaculture

Aquaculture has brought about increased interest in mass production of marine fish larvae. Problems such as poor egg quality and mass mortality of fish larvae have been prevalent. The intensive incubation techniques that often result in bacterial overgrowth on fish eggs could affect the commensal relationship between the indigenous microflora and opportunistic pathogens and subsequently hamper egg development, hatching, larval health, and ongrowth. Little information about the adherent microflora on fish eggs is available, and the present study was undertaken to describe the microbial ecology during egg development and hatching of two fish species of potential commercial importance in marine aquaculture. Attachment and development of the bacterial flora on cod (Gadus morhua L.) eggs from fertilization until hatching was studied by scanning electron microscopy. The adherent microflora on cod (G. morhua L.) and halibut (Hippoglossus hippoglossus) eggs during incubation was characterized and grouped by cluster analysis. Marked bacterial growth could be demonstrated 2 h after fertilization, and at hatching eggs were heavily overgrown. Members of the genera Pseudomonas, Alteromonas, Aeromonas, and Flavobacterium were found to dominate on the surface of both cod and halibut eggs. The filamentous bacterium Leucothrix mucor was found on eggs from both species. While growth of L. mucor on halibut eggs was sparse, cod eggs with a hairy appearance due to overgrowth by this bacterium close to hatching were frequently observed. Vibrio fischeri could be detected on cod eggs only, and pathogenic vibrios were not detected. Members of the genera Moraxella and Alcaligenes were found only on halibut eggs. Caulobacter and Seliberia spp. were observed attached to eggs dissected from cod ovaries under sterile conditions, indicating the presence of these bacteria in ovaries before spawning. Adherent strains did not demonstrate antibiotic resistance above a normal level. Attempts to regulate the egg microflora by incubation of gnotobiotic eggs with defined antibiotic-producing strains did not result in persistent protection against subsequent colonization by the microflora of the incubator.     

Evaluation of five antibiotics on larval gut bacterial diversity of Plutella xylostella (Lepidoptera: Plutellidae)

Larvae of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), have rich microbial communities inhabiting the gut, and these bacteria contribute to the fitness of the pest. In this study we evaluated the effects of five antibiotics (rifampicin, ampicillin, tetracycline, streptomycin sulfate and chloramphenicol) on the gut bacterial diversity of P. xylostella larvae. We screened five different concentrations for each antibiotic in a leaf disc assay, and found that rifampicin and streptomycin sulfate at 3 mg/mL significantly reduced the diversity of the bacterial community, and some bacterial species could be rapidly eliminated. The number of gut bacteria in the rifampicin group and streptomycin sulfate group decreased more rapidly than the others. With the increase of antibiotic concentration, the removal efficiency was improved, whereas toxic effects became more apparent. All antibiotics reduced larval growth and development, and eventually caused high mortality, malformation of the prepupae, and hindered pupation and adult emergence. Among the five antibiotics, tetracycline was the most toxic and streptomycin sulfate was a relatively mild one. Some dominant bacteria were not affected by feeding antibiotics alone. Denaturing gradient gel electrophoresis graph showed that the most abundant and diverse bacteria in P. xylostella larval gut appeared in the cabbage feeding group, and diet change and antibiotics intake influenced gut flora abundance. Species diversity was significantly reduced in the artificial diet and antibiotics treatment groups. After feeding on the artificial diet with rifampicin, streptomycin sulfate and their mixture for 10 days, larval gut bacteria could not be completely removed as detected with the agarose gel electrophoresis method.     

草鱼肠道黏膜厌氧细菌的分离与鉴定

研究以草鱼(Ctenopharyngodon idellus)为实验对象, 运用厌氧培养的方法, 研究了饥饿状态下草鱼肠道黏膜固有微生物的类群及其在不同肠段的分布。实验结果显示草鱼前肠、中肠与后肠中细菌的数量分别是3.17×103、1.63×104和1.79×107 cfu/g。研究共分离到274株单菌落, 经16S rRNA鉴定, 分别属于拟杆菌属(Bacteroides spp.)、鲸杆菌属(Cetobacterium spp.)、梭形杆菌属(Fusobacterium spp.)、气单胞菌属(Aeromonas spp.)、希瓦氏菌属(Shewanella spp.)、芽孢杆菌属(Bacillus spp.)、泛菌属(Pantoea spp.)和柠檬酸杆菌属(Citrobacter spp.)8个种类, 其中专性厌氧细菌的数量占9.1%, 兼性厌氧细菌的数量占90.9%。进一步分析发现, 前肠中只分离到兼性厌氧细菌, 中肠与后肠专性厌氧细菌和兼性厌氧细菌都有分布。专性厌氧细菌Bacteroides paurosaccharolyticus和Bacteroides luti在中肠与后肠都有分布, 而Cetobacterium somerae和Fusobacterium ulcerans只在后肠有发现。兼性厌氧细菌是草鱼肠道黏膜的优势菌群, 其中嗜水气单胞菌Aeromonas hydrophila占73.7%。草鱼肠道不同部位固有厌氧微生物组成存在差异, 细菌数量也明显不同, 后肠中具有更高的细菌丰度和多样性。     

Symbiotic microflora in fishes of different ecological groups

Published data on the taxonomic composition of the intestinal bacterial flora in fishes living under different conditions (marine and freshwater fishes) and differing in the type of feeding are reviewed. The results confirm the conclusion that the composition of intestinal microflora differs depending on fish ecology. A limited number of bacterial taxa found in the intestines of some fish species may be evidence not only for a low diversity of these bacteria but also for insufficient knowledge about them. Considerable differences in the composition of intestinal microflora in marine and freshwater fishes are described.     

The Intestinal Bacterial Community in the Food Waste-Reducing Larvae of <Emphasis Type="Italic">Hermetia illucens</Emphasis>

As it is known that food waste can be reduced by the larvae of Hermetia illucens (Black soldier fly, BSF), the scientific and commercial value of BSF larvae has increased recently. We hypothesised that the ability of catabolic degradation by BSF larvae might be due to intestinal microorganisms. Herein, we analysed the bacterial communities in the gut of BSF larvae by pyrosequencing of extracting intestinal metagenomic DNA from larvae that had been fed three different diets. The 16S rRNA sequencing results produced 9737, 9723 and 5985 PCR products from larval samples fed food waste, cooked rice and calf forage, respectively. A BLAST search using the EzTaxon program showed that the bacterial community in the gut of larvae fed three different diets was mainly composed of the four phyla with dissimilar proportions. Although the composition of the bacterial communities depended on the different nutrient sources, the identified bacterial strains in the gut of BSF larvae represented unique bacterial species that were unlike the intestinal microflora of other insects. Thus, our study analysed the structure of the bacterial communities in the gut of BSF larvae after three different feedings and assessed the application of particular bacteria for the efficient degradation of organic compounds.     

Effect of group size on parasitism in a natural population of the Baltimore checkerspot Euphydryas phaeton

Summary The effect of group size of early instars on parasitism of Euphydryas phaeton (Nymphalidae) was examined. Different numbers of larvae were stocked per web to determine the effect of group size on parasitism. Larval aggregations of moderate size (the size occurring naturally) had the least parasitism. Larger larval groups had a disproportionately high rate of parasitism. The major larval parasitoids located vulnerable larvae within webs, instead of attacking larvae available on the outside of webs. Parasitism rates were similar for larvae of damaged and undamaged webs, a consequence of the behavior and location of larvae in the webs. Lower limit to group size was a function of facilitation of larval numbers in reaching the first feeding site, the top of the host plant. Feeding facilitation by larval aggregations was not a factor in larval survival or growth.     

Maintenance of the supercooled state in the gut fluid of overwintering pyrochroid beetle larvae, Dendroides canadensis : role of ice nucleators and antifreeze proteins

  The effect of gut fluid ice nucleators and antifreeze proteins on maintenance of supercooling was explored in fire-colored beetle larvae, Dendroides canadensis, via seasonal monitoring of supercooling points, antifreeze protein activity and ice nucleator activity of gut fluid and/or larvae. During cold hardening in the field, freeze-avoiding larvae evacuated their guts and depressed larval supercooling points. Analysis of gut fluid indicated supercooling points and ice nucleator activity decreased, whereas antifreeze protein activity increased as winter approached. Suspensions of bacteria isolated from guts of feeding larvae collected in spring/summer had higher supercooling points than those from midwinter-collected non-feeding larvae, suggesting bacterial ice nucleators are removed from midwinter gut fluid. The ice nucleation active bacterium Pseudomonas fluorescens was isolated from gut fluid of feeding larvae but was absent in winter. When mixed with purified D.␣canadensis hemolymph antifreeze proteins (structurally similar and/or identical to those in gut fluid), the cumulative ice nucleus spectra of P. fluorescens suspensions were shifted to lower temperatures indicating an inhibitory effect on the bacteria's ice-nucleating phenotype. By extending larval supercooling capacity, both gut clearing and masking of bacterial ice nucleators by antifreeze proteins may contribute to overwintering survival in supercooled insects. Accepted: 8 August 1996     

Effect of different holding regimens on the intestinal microflora of herring (Clupea harengus) larvae.

The aerobic intestinal microflora of 2-week-old herring (Clupea harengus) larvae was characterized by using conventional microbiological methods and electron microscopy. Larvae were hatched and kept in filtered seawater or in seawater with penicillin and streptomycin. The gastrointestinal tract of herring larvae is essentially a straight tube divided into two compartments. Light microscopy revealed bacteria present in a progressively increasing amount throughout the length of the gastrointestinal tract from esophagus to anus. The posterior region of the intestinal lumen appeared completely occluded with bacteria. The intestinal microflora consisted mainly of members of the genera Pseudomonas and Alteromonas in the larvae incubated in filtered seawater, whereas Flavobacterium spp. dominated in larvae exposed to antibiotics. The intestinal microflora of untreated fish larvae was sensitive to all tested antibiotics, whereas multiple resistance was found in the intestinal microflora of the group given antibiotics. Thus, a dramatic change in the microflora resulted from incubation with antibiotics. Nonpigmented yeasts were detected in both larval groups. Ciliated epithelial cells were observed in the midgut, probably propeling bacteria towards the hindgut, where endocytosis of bacteria has been demonstrated. These findings suggest that transport and sequestering mechanisms resembling those of invertebrates may be found in the gut of fish larvae. The possible significance for larval health and nutrition is discussed.     

基于16S rRNA高通量测序分析大泷六线鱼表皮粘液及肠道内容物微生物多样性

大泷六线鱼(Hexagrammos otakii)是一种具有代表性的高价值冷水性鱼类。通过分析大泷六线鱼表皮粘液及肠道内容物微生物菌群特征,了解其微生物多样性及所携带的自身特有的潜在病原微生物情况。采集设施化车间养殖的大泷六线鱼,提取表皮粘液和肠道内容物基因组DNA,通过16S rRNA高通量测序技术和生物学分析方法,对不同样本的V3+V4区基因文库进行分析。结果表明,大泷六线鱼表皮粘液和肠道内容物样本拥有共同的OTUs为33个,且Venn图呈现了不同来源样本之间的相似性和差异性。Rank-abundance曲线显示了不同样本的均匀度和丰富度,测序数据合理、可信。Alpha指数平均值显示肠道内容物微生物丰富度较高,而表皮粘液微生物多样性较高;Beta多样性显示了不同来源样本间的异质性及同一来源样本间的相似性。从门水平上看,优势菌门均为蓝菌门（Cyanobacteria）、变形菌门（Proteobacteria）、厚壁菌门（Firmicutes）;而属水平结果不同,肠道内容物样本中优势菌属包括Streptophyta、芽孢杆菌属（Bacillus）、杆菌属（Bacillaceae_unclassified）、气单胞菌属（Aeromonas）及弧菌属（Vibrio）,表皮粘液样本中优势菌属包括Streptophyta、气单胞菌属（Aeromonas）、杆菌属（Bacillaceae_unclassified）、香味菌属（Myriudes）、假单胞菌属（Gemmobacter）及弧菌属（Vibrio）。Heatmap热图结果提示,不同微生物菌群结构发挥出不同生物学功能,其中未分类杆菌属、气单胞菌属、弧菌属、假单胞菌属等条件性致病菌的存在均可能导致病害的发生。因此,揭示表皮粘液和肠道内容物样本中微生物的多样性及主要病原菌属的特征对大泷六线鱼健康养殖和疾病防控具有一定的指导意义。     

Influence of larval feeding history on the body condition of Amphiprion melanopus

The cellular condition of liver hepatocytes and the height of gut epithelium cells of larval Amphiprion melanopus were sensitive indicators of feeding condition. Muscle fibres of the trunk showed marked separation in fish fed every third day just prior to settlement. Low feeding regimes also caused reductions in growth, increases in larval duration and reductions in size at metamorphosis. Gut epithelium cell height was also influenced by fish standard length and age. This study suggests that gut epithelium cell height is a useful index for an examination of the importance of starvation of larvae in tropical waters; however, size and age standardization is required prior to comparisons of wild caught fish through time or with laboratory samples.