Colonization of the gut in first feeding turbot by bacterial strains added to the water or bioencapsulated in rotifers

Two bacterial strains, 4:44 and PB52, isolated from turbot(Scophthalmus maximus L.) were used during a first feedingexperiment with turbot larvae. Bacteria were either added directly tothe water on the day of hatching of the larvae (day 0), orbioencapsulated in rotifers (Brachionus plicatilis) distributedon day 2 after hatching. The two bacterial strains were found to bepresent in the water of the rearing tanks throughout the experiment. Theaddition of bacteria influenced the species-composition of themicroflora associated with intensively produced rotifers added to thetanks, and resulted in colonization of the gut of the larvae by theadded bacterial strains. The strain 4:44 showed a peak on day 9 afterhatching, and reached a mean(sem) of 2.5(1.4) × 10⁴bacteria per larva, when added in a mixture with PB52, and 0.4(0.1)× 10⁴ bacteria per larva, when added alone. The strainPB52, on day 12 after hatching, reached 5.2(1.5) × 10⁴bacteria per larva when added in a mixture with strain 4:44, and12.5(0.7) × 10⁴ bacteria per larva, when added alone.The added bacteria colonized the gut turbot larvae, whereas thebacterial land, the survival and growth of the larvae were in most casesnot influenced in a negative way by the addition of bacteria.     

The enrichment and retention of ascorbic acid in rotifers fed microalgal diets

The enrichment and retention of ascorbic acid (AA) was investigated in rotifers Brachionus plicatilis fed on microalgae ( Nannochloropsis oculata and Isochrysis sp. (T.ISO)) and baker's yeast Saccharomyces cerevisiae . The concentrations of AA of the rotifer diets used in the study differed significantly: 4200 μg g⁻¹ of dry weight in Isochrysis sp. (T.ISO), 2600 μg g⁻¹ in N. oculata and only 77 μg g⁻¹ in S. cerevisiae . Rotifers contained 620 μg AA g⁻¹ prior to the experimental feeding. When subsequently fed for 3 h on microalgae at a ration of 0.13 mg dry microalgae per 10⁶ rotifers rapidly and efficiently increased their content of AA: Isochrysis sp.-fed rotifers contained 1600 μg AA g⁻¹ and N. oculata -fed rotifers contained 1100 μg AA g⁻¹. Concentrations were boosted by a further feeding of a second ration of algae at three times the initial feeding ration; 21 h later, Isochrysis sp.-fed rotifers contained 2500 μg AA g⁻¹ and N. oculata -fed rotifers contained 1700 μg AA g⁻¹. This represented a 180% and 310% increase in the pre-feeding vitamin concentrations in Isochrysis sp. and N. oculata -fed rotifers, respectively. There were no significant changes in AA concentration in rotifers fed a similar ration of yeast throughout the feeding period (520-620 μg AA g⁻¹). Rotifers retained AA during a subsequent 24 h non-feeding period, with no significant changes in the concentrations in any of the rotifer groups. The production of rotifers rich in AA may be particularly valuable for the culture of fish larvae that have a high requirement for the vitamin.     

Enrichment of Rotifers Brachionus plicatilis with Eicosapentaenoic Acid and Docosahexaenoic Acid Produced by Bacteria

Abstract— Two bacterial strains, rich in either eicosapentaenoic acid [EPA, 20:5(n-3)] ( Shewanella gel-idimarina ACAM 456) or docosahexaenoic acid [DHA, 22:6(n-3)] ( Colwellia psychroeryrhrus ACAM 605) were tested for their ability to enrich rotifers Erachionus plicatilis in these polyunsaturated fatty acids. Rotifers were exposed for 24 h to each bacterial strain and to a mixture of the two strains. They were then harvested and their fatty acid compositions were analysed and compared to those of rotifers that had been either starved or fed yeast Saccharomyces cerevisiae or microalgae Tetraselmis suecica in 2-L glass flasks. Exposure to 1.4 × 10⁹ cells/ml of the EPA-producing bacterium only resulted in rotifer EPA levels increasing from 0.1% to 1.2% of total dry weight (%dw). Similarly, following exposure to 1.0 × 10⁹ cells/mL of the DHA-producing bacterium only, rotifer DHA levels increased from below detection to 0.1% dw. When exposed to a mixture of the two bacterial strains, containing 7.0 × 10⁸ celldml of the EPA producer and 5.0 × 10⁸ cells/mL of the DHA producer, the rotifers'final EPA and DHA levels were 0.5% dw and 0.3% dw respectively. Although feeding strategies need refining, these results show, for the first time, that rotifers can be enriched with DHA from bacteria, and that rotifers can be enriched simultaneously with both DHA and EPA from different bacterial strains.     

Elimination of the associated microbial community and bioencapsulation of bacteria in the rotifer Brachionus plicatilis

The bioencapsulation of live bacteria in the rotifer Brachionus plicatilis was determined under monoxenic conditions. The first objective was to evaluate the microbiota of the rotifer during intensive production and to obtain sterile rotifer cultures starting from adult females or amictic eggs using PVP-Iodine, Hydrogen peroxide or antibiotic mixtures. In the rotifers, the proportion of vibrios increased significantly during the mass production, displacing other unidentified marine bacteria. Rotifers, in the absence of culturable bacteria were obtained starting from amictic eggs and using Trimetroprim-sulfametoxasole (Bactrim Roche®) at 10 ml l^–1. The effect of members of Vibrionaceae on the survival and growth rate of rotifers was determined under monoxenic conditions. The survival of rotifers was not affected in the presence of different isolates, while amictic egg formation occurred and the populations increased when the strains Vibrio proteolyticus C279 and Aeromonas media C226 were tested. All isolates were successfully incorporated in the rotifers, since there was no significant difference between the numbers of bioencapsulated cells of different strains of isolates. The results show that it is possible to replace the microbial community in rotifer cultures, started from disinfected amictic eggs, with selected bacterial strains. This could be used as a tool for future studies to reveal the role of specific bacteria on first larval stages of marine fish species.     

Rotifers fed various diets of baker''s yeast and/or Nannochloropsis oculata and their effect on the growth and survival of striped mullet (Mugil cephalus) and milkfish (Chanos chanos) larvae

The rotifer Brachionus plicatilis (S-type Hawaiian strain) was cultured with various combinations of baker's yeast and Nannochloropsis oculata. There were no significant differences in the daily rotifer production and amino acid profiles of the resulting rotifers. The significantly lower levels of fatty acids (C14, C16, C20:4n−6, C20:5n−3 and C22:6n−3) observed in the rotifers were found to correspond with the amount of yeast presented in their diet. The low survival and growth of striped mullet larvae recorded at Day 15 posthatching indicates that rotifers fed only yeast were nutritionally deficient in fatty acids. The fatty acid requirements of mullet, however, appeared to be satisfied with rotifers cultured on a combination of yeast and N. oculata. In contrast, no significant differences in larval milkfish survival and growth at Day 10 posthatching were detected when using rotifers fed the various diets in the larval rearing protocol.     

Effects of astaxanthin on Brachionus manjavacas (Rotifera) population growth

Astaxanthin is a red secondary carotenoid and powerful antioxidant that is used in aquaculture to enhance colour and improve fish health. Brachionid rotifers are often used as a live feed for larval fish, but do not contain endogenous carotenoids. However, they can be enriched with astaxanthin through their diet and transfer it to larval predators. When supplemented with 2 μg/ml astaxanthin oleoresin extracted from the green alga Haematococcus pluvialis, Brachionus manjavacas rotifer cultures reached significantly higher population densities and maintained them for longer. Furthermore, data are presented that exposure to oleoresin or pure astaxanthin enhances rotifer resistance to oxidative stress, a common cause for the collapse of rotifer mass cultures. Astaxanthin can be visualized in the gut of the rotifers, allowing the time course of uptake to be estimated by image analysis. Using this method, it was found that accumulation of astaxanthin in the rotifer gut saturates after 1.5 hr of exposure. The bioactive dose of astaxanthin oleoresin for rotifers was found to be 1–20 μg/ml. Astaxanthin concentration in rotifer tissues was measured using absorbance spectrophotometry. It was found that treating rotifers with 20 μg/ml for 24 hr; the concentration of astaxanthin absorbed into rotifer tissues was 2.6 mg/g. Overall, these experiments indicate that astaxanthin extracted from H. pluvialis can be used to improve the productivity and stability of rotifer mass cultures by increasing oxidative stress resistance and enhance the nutritional content of rotifers for larval fish.     

Strategies for Development of Rotifers as Larval Fish Food in Ponds

Strategies to sustain rotifer peak biomass, distribution of rotifer resting eggs in the sediment, and relationship between rotifers and larval fish growth were studied in a series of pond experiments. After the ponds were filled with water, herbivorous rotifers (e.g., Brachionus calyciflorus ) developed first, but were gradually replaced by predatory rotifers (e.g., Asplanchna ). Subsequently, herbivorous cladocerans (e.g., Moina sp) eventually replaced rotifers and dominated the zooplankton community. The occurrence of Asplanchna and Moina indicated the decline of B. calyciflorus . Peak rotifer biomass developed 8–10 d after the ponds were filled with water at 20–25 C, 10–15 d at 17–20 C, 15–20 d at 15–17 C, 20–30 d at 10–15 C, and >30 d at < 10 C. The abundance of resting eggs in the top 5-cm sediment varied from 6 to 83/cm². About 25% of resting eggs were buried in the top 5-cm sediment but the number of resting eggs decreased with increased sediment depth. Optimum rotifer biomass for silver carp Hypophthalmichthys molitrix larvae stocked at 1,500,000/ha was 20–40 m/gL. High rotifer biomass (>20 mg/L) usually lasted 3–5 d, but could be prolonged by pond fertilization or cladoceran controls. A weekly application of dipterex at 0.05 mg/L reduced cladoceran biomass but enhanced rotifer biomass. Our results indicate with a careful management plan it is possible to synchronize the rotifer development with larval fish stocking.     

大菱鲆仔稚鱼发育早期肠道菌群结构形成的影响因素

为研究鱼类发育早期肠道菌群结构的演变过程及影响因素,运用高通量测序技术,分析了处于不同发育阶段的大菱鲆(Scophthalmus maximus)仔稚鱼肠道、受精卵、不同类型的饵料和水源中的菌群结构,以及它们之间的相关性。结果显示,以不同的OTU(Operational Taxonomic Units,可操作分类单元)作为分类依据,发现大菱鲆仔稚鱼的肠道菌群结构在开口摄食后不久已趋于稳定,其优势菌与受精卵所携带的细菌关联较大。并且在大菱鲆仔稚鱼不同的发育时期,这一菌群的结构非常稳固,几乎不受水和饵料中优势细菌的影响而发生改变。乳球菌属的Lactococcus piscium菌株一直是大菱鲆仔稚鱼肠道中的优势菌种,在不同发育时期的优势度高达45%~65%。本研究还发现,大菱鲆仔稚鱼肠道可能对定植的菌种具有选择性,一些水环境和饵料中的非优势菌,如Streptococcus sp.,Pseudomonas sp.,Carnobacterium sp.等细菌也会定植于肠道,成为大菱鲆肠道中的次优势菌。     

Bacterial diversity of tilapia (Oreochromis niloticus) cultured in brackish water in Saudi Arabia

The bacterial flora occurring in brackish pond water, sediment, gills and intestine of healthy tilapia cultured in Saudi Arabia were estimated both quantitatively and qualitatively, and the isolates were identified to genus or species level. Total viable count of bacteria ranged from 1.4±1.5×10³ to 8.6±2.7×10³ cfu ml⁻¹; 1.2±3.1×10⁶ to 7.3±1.1×10⁷ cfu g⁻¹; 8.7±1.9×10⁵ to 2.1±0.9×10⁶ cfu g⁻¹; and 2.8±2.4×10⁷ to 1.0±1.6×10⁸ cfu g⁻¹ in the pond water, sediment, gills and intestine of brackish water tilapia, respectively. In total, 19 bacterial species were identified. The bacteria were predominantly Gram-negative rods (87%). Pond water and sediment bacteria influenced the bacterial composition of gills and intestine of tilapia. In contrast to gill bacteria, more diversification was observed in intestinal bacteria. The predominant (prevalence >10%) bacterial species were Vibrio parahaemolyticus, Vibrio carchariae, Vibrio alginolyticus, Chryseomonas sp., Vibrio vulnificus, and Streptococcus sp. in all the populations with the exception of the sediment population where Streptococcus sp. was replaced by Shewanella putrefaciens. Vibrio spp. (58% of the total isolates) dominated the total bacterial population.     

Evaluating bioencapsulation of florfenicol in rotifers (Brachionus plicatilis)

The rotifer Brachionus plicatilis is one of the most important live‐feed organisms used in the larval culture of marine fish. Bioencapsulation of florfenicol in rotifers was investigated by delivering it directly to the organisms as particles and the doses ranged from 50 to 1000 mg L^?1. Analysis of the florfenicol concentrations in rotifers was performed using high‐performance liquid chromatography. The uptake increased with the dose and the enrichment time, and the highest concentration achieved in this study, 1.25 ng rotifer^?1, was obtained using a dose of 1000 mg L^?1 and 150 min of enrichment. The optimal time for satisfactory enrichment of rotifers with florfenicol was found to be dose dependent and ranged from 30 to 120 min for doses between 400 and 800 mg L^?1. The parameters affecting the concentrations achieved in rotifers were the size of the florfenicol particles, enrichment time and dose.     

Ingestion of Artemia nauplii by Chinese mitten crab Eriocheir sinensis zoea larvae

A series of ingestion trials were conducted to determine the ingestion rate of Artemia nauplii by Eriocheir sinensis zoea larvae with increasing densities of Artemia and with or without rotifers as a co-feed. At each zoeal stage, 10 groups of 10 larvae were reared individually in glass beakers and fed with increasing densities of newly hatched Artemia nauplii (0.5, 2.5, 5, 10 and 20 individual (ind.) mL⁻¹) with or without rotifers (15–25 ind. mL⁻¹) as a co-feed. The average number of ingested Artemia was measured over 24 h. In addition, the average larval development rate (Larval Stage Index, LSI) over a longer period (time needed for the best treatment to reach 100% moult or metamorphosis to the next larval stage) was compared. The results showed that Artemia ingestion rate of E. sinensis larvae increased with increasing prey densities and larval development, and had a significantly negative correlation with rotifer consumption for all zoeal stages. Rotifers as an alternative prey significantly affected the intake of Artemia at early larval stages (Z1 and Z2) and promoted LSI at a lower Artemia density. Further experiments are needed to clarify the effect of prey density on survival and larval development when larvae are reared communally.     

An aerolysin-like enterotoxin from Vibrio splendidus may be involved in intestinal tract damage and mortalities in turbot, Scophthalmus maximus (L.), and cod, Gadus morhua L., larvae

Vibrio splendidus is a pathogen that can cause major losses during the early stages of larval turbot rearing when live feed (rotifers or Artemia) is used. As haemolytic bacteria have often been associated with larval rearing losses, we studied the role of the V. splendidus haemolysin in infection of larvae. From a bank of over 10,000 transposon mutants of V. splendidus, two different types of haemolysin-negative mutants were obtained. Both had lost virulence for larval fish, and immunohistochemistry showed that the transposon mutant studied colonized the turbot larval intestinal tract at a similar level to the wild-type organism but did not cause damage or signs of enteritis found with the wild-type organism. One transposon insertion site was located within a gene with high homology to aerolysin, the cytolytic toxin produced by several Aeromonas spp. The haemolysin, which we have termed vibrioaerolysin, had properties similar to aerolysin and osmotic protection studies showed that it formed pores in the membranes of erythrocytes of similar diameter to those of aerolysin. The Tn10 insertion site of the second transposon mutant was in an adjacent ToxR-like gene, suggesting that this might control expression of the vibrioaerolysin. The gastroenteritis caused by Aeromonas spp. in humans is considered to be due to production of aerolysin causing cyclic AMP-dependent chloride secretion in cells of the gastrointestinal tract. Damage to the intestinal tract of marine fish larvae could occur in a similar way, and it is possible that several Vibrio spp. found in the developing bacterial flora of the larval fish gut can secrete aerolysin-like toxins leading to death of larvae in the early rearing stages. Routine bacteriological screening on blood agar plates of live feed is recommended with measures to reduce the concentrations of haemolytic bacteria in rearing systems.     

Effect of different algae used for enrichment of rotifers on growth, survival, and swim bladder inflation of larval amberjack Seriola dumerili

The effect of algae with different DHA contents used for the enrichment of rotifers on the growth performance, survival, and swim bladder inflation of larval amberjack Seriola dumerili was investigated. Rotifers were enriched with freshwater Chlorella vulgaris containing three levels of DHA (rotifer containing DHA 0.04, 0.60, 1.32?g DHA 100?g^?1 DM) and Nannochloropsis (0.04?g DHA 100?g^?1 DM; 2.54?g EPA 100?g^?1DM). The larvae were fed the enriched rotifers in triplicate from 3?days post-hatch for 7?days in static condition. The same algae used for rotifer enrichment were supplied to the larval tanks. Growth and survival rate of fish fed the rotifers enriched with Nannochloropsis were higher than those of fish fed the rotifers enriched with all three Chlorella treatments. Swim bladder inflation was lowest in fish fed the rotifers enriched with Nannochloropsis. The proportion of EPA was higher in fish fed the rotifers enriched with Nannochloropsis, while that of DHA increased proportionally with the DHA levels in the rotifers enriched with Chlorella. These results suggest that rotifers enriched with Nannochloropsis (EPA-rich rotifers) are effective to enhance growth and survival, but DHA instead of EPA is essential to improve the swim bladder inflation in amberjack larvae.     

Fundamental studies on the physiology of rotifers in mass culture—V. Dry Chlorella powder as a food for rotifers

The dietary value of dried, commercial Chlorella was compared with that of living marine Chlorella, and yeast, in relation to growth of the rotifer Brachionus plicatilis raised individually and by batch culture methods.A concentration of 50 μg/ml of dried Chlorella powder is near an optimal density for rotifer growth. The dried material in suspension is less effective for growth than living marine Chlorella, although it is much more effective than a suspension of yeast at the same density (50 μg/ml).In batch culture (12-l glass vessel), the rotifers grew from an initial inoculation of 13.2 individuals/ml to a density of 434 individuals/ml by the 16th day. About 10⁷ rotifers could be removed from one batch culture in five harvests in the 41-day experimental period.The results indicate that dried Chlorella powder is an effective food for the rotifer Brachionus plicatilis.     

Microbially matured water: a technique for selection of a non-opportunistic bacterial flora in water that may improve performance of marine larvae

Before transfer to larval incubators, water was membrane filtered to remove >95% of the bacteria and then transiently maintained in a biofilter that promoted recolonization of the water by non-opportunistic bacteria. The process is termed microbial maturation of the water. Hypothetically the bacterial flora in the matured water should protect the marine larvae from colonization and proliferation by opportunistic bacteria. Testing of the hypothesis demonstrated 76% higher survival of yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus) in matured than in membrane filtered water. Proliferation of opportunistic bacteria was observed in the rearing water after hatching of turbot eggs (Scophthalmus maximus), but to a less extent in the microbially matured water. In the early phase of first feeding of turbot larvae, the matured water induced qualitative differences in the gut microflora. Significantly higher initial growth rate of the turbot larvae in the matured water affected 51% higher average weight of 13 days old larvae than in membrane filtered water. Algal addition to the matured water enhanced the larval growth further. The experiments conducted supported the proposed hypothesis that microbial maturation selects for non-opportunistic bacteria, which protects the marine larvae from proliferation of detrimental opportunistic bacteria.     

Comparison of rotifer culture quality with yeast plus oil and algal-based cultivation diets

The culture quality of rotifers, Brachionus plicatilis, was compared for yeast and algal-based cultivation diets. The rotifer quality was evaluated based on factors which may affect survival and growth of marine fish larvae, including individual length and biomass, nutritional value, bacterial content, and rotifer viability. The diets used were monocultures of Tetraselmis sp., Isochrysis galbana, Pavlova lutheri, and baker's yeast plus capelin oil.Rotifers grown to early stationary phase with equal food rations exhibited equal length distribution, but the rotifer individual biomass was 10–25% higher for yeast-grown rotifers than for algal-grown rotifers.All diets gave equal protein content of individual rotifers. The lipid content was slightly higher and the ratio of protein to lipid was slightly lower with yeast plus capelin oil than with algae. The fatty acid composition of the rotifers was closely related to that of their dietary lipids and the 3 fatty acid content was not systematically different for the two types of diets.Use of yeast plus capelin oil resulted in considerably higher numbers of both suspended and rotifer-associated bacteria than with use of algal diets. No differences were found for the algal species involved. The viability of the rotifers in a temperature and salinity test was far better in groups fed algae than in groups fed yeast plus capelin oil.The results indicated an overall better quality of rotifers cultivated with algae than for rotifers cultivated with yeast and oil. Questions related to proteins and the microflora of rotifers should be further emphasized in future research.     

The Culture of the Rotifer Brachionus plicatilis with Chlorella vulgaris Containing Vitamin B12 in its Cells

The rotifer Brachionus plicatilis requires vitamin B₁₂. Freshwater Chlorella , which is produced by traditional culture, cannot support rotifer growth under bacteria-free conditions. However, Chlorella enriched with vitamin B₁₂ can support rotifer growth. To attain stable mass production of Brachionus , it is desirable to develop a food that can completely support growth of the rotifers. The authors cultured rotifers at experimental and mass culture scale with concentrated Chlorella vulgaris suspension enriched with vitamin B₁₂ in their cells.
Chlorella suspensions were prepared containing different amounts of vitamin B₁₂ in their cells, and rotifers were then cultured in 20 ml of the prepared suspensions. The highest rotifer yield was obtained from the group cultured with Chlorella containing more vitamin B₁₂ in their cells. The suitable content of vitamin B₁₂ in the concentrated Chlorella suspension commercially available for mass culture of the rotifer is considered to be 200 _μg per 100 g dry matter of Chlorella . The amount of vitamin B₁₂ necessary to produce one individual rotifer is calculated at 0.32 pg.
The authors conducted mass production of the rotifer with baker's yeast and refrigerated concentrated Chlorella containing vitamin B₁₂ Rotifer culture with vitamin B₁₂ was more stable and showed 1.3 times higher production than with normal Chlorella .     

Optimum Feeding Rate of the Rotifer Brachionus plicatilis on the Marine Alga Nannochloropsis sp.

The optimum feeding rate of the rotifer Bruchionus plicutilis was investigated to determine the best conditions for growth of the rotifer, and also in order to maintain good water quality of the culture. Fifty rotifers of a large size strain were cultured individually at five food density levels of Nannoehloropsis sp. (0.5 ± 10⁶, 1.5 ± 10⁶, 3 ± 10⁶, 5 ± 10⁶, and 8 ± 10⁶ cells/ml). At each level, daily survival and offspring production were recorded until the death of the final individual. The data obtained were analyzed by the life table method. The maximum value of three growth indices (the net reproduction rate, mean life expectancy at age 0, and intrinsic rate of increase) was obtdned at the food density of 1.5 ± 10⁶ cells/ml. The ration size was calculated to be 325% (dry weight)/ day, which is equivalent to about 70% of the saturated feeding rate. It was suggested that the feeding rate should be controlled to lower than the saturated value for an efficient mass culture.     

Effects of secondary crops on bacterial growth and nitrogen removal in shrimp farm effluent treatment systems

Secondary crops provide a means of assimilating some effluent nitrogen from eutrophic shrimp farm settlement ponds. However, a more important role may be their stimulation of beneficial bacterial nitrogen removal processes. In this study, bacterial biomass, growth and nitrogen removal capacity were quantified in shrimp farm effluent treatment systems containing vertical artificial substrates and either the banana shrimp Penaeus merguiensis (de Man) or the grey mullet, Mugil cephalus L. Banana shrimp were found to actively graze biofilm on the artificial substrates and significantly reduced bacterial biomass relative to a control (24.5±5.6 mg C m⁻² and 39.2±8.7 mg C m⁻², respectively). Bacterial volumetric growth rates, however, were significantly increased in the presence of the shrimp relative to the control (45.2±11.3 mg C m⁻² per day and 22.0±4.3 mg C m⁻² per day, respectively). Specific growth rate, or growth rate per cell, of bacteria was therefore appreciably stimulated by the banana shrimp. Nitrate assimilation was found to be significantly higher on grazed substrate biofilm relative to the control (223±54 mg N m⁻² per day and 126±36 mg N m⁻² per day, respectively), suggesting that increased bacterial growth rate does relate to enhanced nitrogen uptake. Regulated banana shrimp feeding activity therefore can increase the rate of new bacterial biomass production and also the capacity for bacterial effluent nitrogen assimilation. Mullet had a negligible influence on the biofilm associated with the artificial substrate but reduced sediment bacterial biomass (224±92 mg C m⁻²) relative to undisturbed sediment (650±254 mg C m⁻²). Net, or volumetric bacterial growth in the sediment was similar in treatments with and without mullet, suggesting that the growth rate per cell of bacteria in grazed sediments was enhanced. Similar rates of dissolved nitrogen mineralisation were found in sediments with and without mullet but nitrification was reduced. Presence of mullet increased water column suspended solids concentrations, water column bacterial growth and dissolved nutrient uptake. This study has shown that secondary crops, particularly banana shrimp, can play a stimulatory role in the bacterial processing of effluent nitrogen in eutrophic shrimp effluent treatment systems.     

Contaminant washout in a hydraulically integrated serial turbidostat algal reactor (HISTAR)

A hydraulically integrated serial turbidostat algal reactor (HISTAR) was mathematically modeled and designed for large-scale production of microalgae. HISTAR, which combines turbidostats with a series of continuous-flow stirred-tank reactors (CFSTRs), was designed with contaminant mitigation as a primary design parameter. The concept of contaminant mitigation in the series of CFSTRs is discussed and three mathematical models presented to predict contaminant washout within the CFSTRs. Model simulations indicated that the hydraulic regime within each CFSTR is crucial to the contaminant mitigation process in the series of CFSTRs. Experiments on the HISTAR system with a liquid volume of about 8500 l, culturing Chaetoceros muelleri (CHAET 10), demonstrated that 0.8 million live rotifers, intentionally added to the first CFSTR, were washed out of the six CFSTRs at a local dilution rate of 4 day⁻¹. In another experiment, Thalassiosira sp. cultured at a dilution rate of 0.667 day⁻¹ fell victim to a few rotifers that inadvertently entered the CFSTRs. The validity of the washout concepts was demonstrated further when the ≈300 million live rotifers in the CFSTRs were completely washed out by simply increasing the dilution rate to 4 day⁻¹.