Dual disease resistance in a selectively bred eastern oyster, Crassostrea virginica, strain tested in Chesapeake Bay

Selective breeding efforts have yielded oyster strains, Crassostrea virginica, with improved survival and resistance against Haplosporidium nelsoni (MSX); however, because of susceptibility to the oyster pathogen Perkinsus marinus (Dermo), their utility has been limited in areas where the two parasites co-occur. Dual resistance to H. nelsoni and P. marinus was achieved through four generations of artificial selection of wild Delaware Bay oyster progeny at a site in the lower York River, Virginia, USA where both diseases are enzootic. During 1993–1995, survival, growth, and disease susceptibility of third generation Delaware Bay (F₃-DEBY) oysters were evaluated at the York River site in comparison to that of similarly selected third generation James River, Virginia oysters (F₃-JR), and first generation Louisiana oysters (F₁-LA), whose parents were naturally selected in the wild for resistance to P. marinus. During 1997–1999, the performance of F₄-DEBY was evaluated at three sites in Virginia in comparison to two groups of first generation oysters whose parents originated from Mobjack Bay and Tangier Sound, Virginia where both P. marinus and H. nelsoni are enzootic. In the presence of high infection pressure from both H. nelsoni and P. marinus, the F₃-DEBY stock showed significantly higher survival and growth than either the F₃-JR or F₁-LA strain. After 15 months of deployment, 79% of F₃-DEBY, 11% of F₃-JR and 17% of F₁-LA oysters were market size (≥76.2 mm) and cumulative mortality was only 16% in F₃-DEBY as compared to 42% in F₃-JR and F₁-LA. At the termination of the study, F₃-DEBY oysters exhibited 22% lower mortality than the F₁-LA stock, which outperformed the F₃-JR stock. Relative performance in respect to disease varied considerably with sample date; however, average H. nelsoni weighted prevalence varied such that F₃-DEBY1-LA=F₃-JR and average P. marinus weighted prevalence varied such that F₁-LA3-DEBY3-JR. In the 1997–1999 trial, F₄-DEBY oysters experienced 34–61% lower mortality, greater growth rate, and consistently lower prevalence and intensity of P. marinus than either Mobjack Bay or Tangier Sound oysters. H. nelsoni prevalences were very low (<12%) in all three stocks. This is the first study to demonstrate that reduced susceptibility to both P. marinus and H. nelsoni can be achieved through selective breeding.     

The effets of feed water flow rate on the growth of aquacultured Crassostrea virginiea in Hawaii

Selected nursed C. virginica with an initial average weight of 3.59 g were grown in vertical suspension in a tank which was divided into three chambers. The oysters were divided into three groups, glued onto strips of polyvinyl chloride and suspended in the three chambers. They were fed commercial shrimp pond effluent at the following flow rates: 4.00 liter/ day/g (high), 1.33 liter/day/g (medium), and 0.45 liter/day/g (low)^*. After 209 days the final average weights of the oysters were 66.43 g, 53.67 g and 40.65 g. The average recorded dissolved oxygen concentrations of the effluent of the three chambers were 7.0 ppm, 6.0 ppm and 5.2 ppm, respectively. The survival rates were 90.56, 73.33 and 52.12% and the percentages of oysters 55 g or larger on the harvesting day were 91.67, 76.69 and 8.33% for the high, medium and low feed water flow rates. Up to an average weight of about 20 g, there was no significant difference between the growth rate of the oysters receiving 4.00 liter/day/g and those receiving 1.33 liter/day/g. All of the oysters grew rapidly during a period of increased temperature and decreased salinity towards the end of the grow-out period.     

Short term effects of a commercial eastern oyster nursery upon nutrient and plankton dynamics of a coastal embayment: observations from mesocosm experiments

Two mesocosm experiments were conducted to study the interaction of a commercial oyster‐nursery system with the surrounding embayment, specifically, nutrient and plankton dynamics. The nursery was stocked with 80–200 L of oysters, sized 3–5 mm. Ambient water and the water passed through the oyster nursery were incubated in mesocosms, and nutrients and plankton were monitored over the course of 27‐h incubations. The first experiment conducted in July 2009 captured a phytoplankton community dominated by Peridinium quinquecorne, a rare dinoflagellate not previously reported in the northeastern USA. Dissolved nitrogen compounds in all mesocosms were depleted within the first 6 h. The second experiment was conducted in September 2009, when a more typical and diverse phytoplankton community was present. Unlike the first experiment, Nitrate plus nitrite in the mesocosms was not depleted. Both experiments indicated little difference between the water passed through the oyster nursery and the ambient water in terms of subsequent nutrient and plankton dynamics, indicating little ‘legacy effect’ of the oyster nursery upon nutrients and plankton in this embayment. This conclusion was reached under the specific operating conditions typical for this nursery system, as chosen by the commercial partner in the study; changes in oyster stocking or flow rate are likely to change the results.     

Use of effluent water from fish-ponds as a food source for the Pacific oyster, Crassostrea gigas Thunberg

Abstract. Growth rates, condition indices and diet composition of the Japanese oyster, Crassostrea gigas Thunberg, were studied in two types of ponds which form part of a fish-bivalve integrated culture system. Although abiotic parameters (e.g. temperature, salinity, pH, ammonia, particulate inorganic matter) were similar in the two pond types, oysters supplied with water from a sedimentation pond grew significantly faster and showed better condition indices than the oysters supplied with water from the PVC-lined ponds. It is suggested that the main reasons for the better performance of the oysters supplied with water from sedimentation pond water are: higher algal diversity, additional nutritious Food consisting of attached benthic diatoms and stable algal concentration.     

The impact of varying feeding regimes on oxygen consumption and excretion of carbon dioxide and nitrogen in post-smolt Atlantic salmon Salmo salar L.

Oxygen consumption, carbon dioxide excretion and nitrogen excretion from 2 kg Atlantic salmon Salmo salar L. were studied at land-based outdoor tanks, throughout a 10 day period. Fish were fed six feed rations (0 [fasting fish], 0.15, 0.30, 0.45, 0.60 and 0.75% BW day^-1) of commercially extruded dry feed at two provision regimes: between 07.00-09.00 h and 19.00–21.00 h (periodic feeding); and between 07.00-21.00 h (continuous feeding). Fish were acclimatized to the feeding regime for 5 days prior to the start of the experiment. From days 5 to 10 of the study, oxygen consumption was measured automatically every 15 min. During day 10, carbon dioxide excretion, ammonia and urea excretion were measured hourly throughout a 24 h period. During the experiment, the water temperature and salinity were 8.5C and 33.5 ppt, respectively. Significant linear relationships between feed ration and metabolic rates were evident. Increased feed ration influenced oxygen consumption, carbon dioxide excretion, ammonia and urea excretion, ammonia quotient and the respiration quotient, proportionally. The two feed provision regimes caused the establishment of different daily rhythms in metabolic excretion. Only small differences in total daily excretion were however recorded for each feed ration. Ammonia and respiratory quotient results clearly showed that fish became more dependent on fat oxidation as an energy source, when feed was restricted.     

体重对青海湖裸鲤排氨率和排氨量的影响

为了解体重对青海湖裸鲤(Gymnocypris przewalskii)排氨率和排氨量的影响,在21℃左右的水温下,结合对青海湖裸鲤耗氧率和呼吸频率的测定,采用酚盐分光光度法测定并研究了不同体重下青海湖裸鲤的排氨量、排氨率。结果表明:不同体重的青海湖裸鲤在基础呼吸代谢过程中其排氨量方面有极显著的差异(P<0.01)。青海湖裸鲤的排氨量随着体重的增加而增加,呈幂指数关系。不同体重的青海湖裸鲤的排氨率等也有显著差异(P<0.01),随着体重的增加排氨率相对降低。     

海水酸化胁迫对紫贻贝能量分配的影响

2016年5～6月在山东桑沟湾楮岛海区,采用野外围隔和现场流水相结合的方法,以紫贻贝(Mytilus galloprovincialis)为研究对象,以pH为8.0作为对照组,探讨了酸化胁迫(p H=7.7)对其能量分配的影响。结果显示,短期(10d)海水酸化胁迫下,紫贻贝的滤水率、同化效率、氧氮比显著下降(P0.05),排氨率极显著增加(P0.01),耗氧率无显著差异(P0.05);中期(30d)海水酸化胁迫下,紫贻贝的滤水率和氧氮比显著下降(P0.05),而同化效率、耗氧率、排氨率显著升高(P0.05)。能量收支的结果显示,短期(10 d)酸化胁迫下,紫贻贝的摄食能和吸收能显著降低(P0.05),呼吸能无显著差异(P0.05),排泄能显著增加(P0.05),生长余力极显著降低(P0.01);中期(30d)海水酸化胁迫下,摄食能降低(P0.05),吸收能、呼吸能、排泄能、生长余力显著升高(P0.05)。氧氮比的结果显示,在海水酸化胁迫下,氧氮比的波动范围为14.28～20.46,贝类体内的供能物质由脂肪和碳水化合物逐渐向蛋白质过渡。研究结果为揭示紫贻贝应对海水酸化胁迫的生理响应提供了基础数据。     

Impact of farming intensity and water management on nitrogen dynamics in intensive pond culture: a mathematical model applied to Thai commercial shrimp farms

A mathematical model is used to investigate the impact of farming intensity and water management on nitrogen dynamics in the water column of intensive aquaculture ponds. The model describes the input of ammonia, its assimilation by phytoplankton or nitrification, and the loss of nitrogen through sedimentation, volatilization, and discharge. The model is calibrated for two commercial shrimp (Penaeus monodon Fabricius) farms in Thailand. Assimilation by phytoplankton with subsequent sedimentation or discharge is the principal process of ammonia removal. When inputs of ammonia exceed the algal assimilation capacity (carrying capacity), nitrification and volatilization of excess ammonia become significant. Carrying capacity is negatively affected by non-chlorophyll turbidity, and was estimated as 6 t ha^?1 cycle^?1 at a non-chlorophyll extinction of 2.6 m^?1. In ponds managed within their carrying capacity, ammonia concentrations are lowest at no water exchange, reach a maximum at exchange rates between 0.2 and 0.4 day^?1, and decline again at higher rates. When the carrying capacity is exceeded, excess ammonia concentrations decline continuously with increasing water exchange. Average exchange rates used in intensive shrimp farms (up to 0.2 day^?1) reduce phytoplankton abundance and sedimentation within ponds, but not ammonia concentrations. Discharges are high in particulate nitrogen at water exchange rates up to 0.3 day^?1, but contain mainly dissolved nitrogen at higher rates.     

Influence of starvation, body size and temperature on ammonia excretion in the marine bivalve Tapes decussatus (L.)

Abstract. Ammonia excretion rate of the marine bivalve Tapes decussatus (L.) varied with body weight, temperature and starvation. There was a steady state in the excretion rates, in which these rates neither increased nor decreased during the first 6 days of starvation. The highest rates of ammonia excreted during the steady state (before decline to lower level) depended on the temperature (715 ± 86 and 395 ± 55 μg NH₄.N/clam/h × 10⁻²) at 28°C and 20°C, respectively. At 16°C, the steady state extended from 6h to 18d starvation. Ammonia excretion rates were higher for starved clams than for fed clams at all sizes, e.g. clams of 0·07 g dry flesh weight (28 ± 9 and 13 ± 5 μg NH₄.N/clam/h × 10⁻² respectively) at 16°C but not at 20°C and 28°C. At each temperature, weight-specific ammonia excretion rates were related to dry flesh weight of starved clams but were not related to fed ones.     

Feeding has the largest effect on the ammonia excretion rate of the southern rock lobster, Jasus edwardsii, and the western rock lobster, Panulirus cygnus

The total ammonia nitrogen (TAN) excretion of spiny lobsters Jasus edwardsii and Panulirus cygnus, was determined in relation to temperature, body weight, emersion, daily rhythm and feeding. Temperature and body weight had large influences on the rate of TAN excretion. Exponential relationships were found between temperature (T) and TAN excretion of both species. These were described by the following equations: J. edwardsii Log₁₀ TAN=0.041T−3.57 (r²=0.979, F=143.2, P=0.001), P. cygnus Log₁₀ TAN=0.057T−3.90 (r²=0.987, F=302.2, P<0.001). TAN excretions of both species were positively correlated to body weight (W), and the relationships were described by the following equations: J. edwardsii Log₁₀ TAN=0.473 log₁₀ W−1.704 (r²=0.42, F=14.05, P=0.001), P. cygnus Log₁₀ TAN=0.499 log₁₀ W−1.346 (r²=0.69, F=44.18, P<0.001). TAN excretion increased significantly when lobsters were re-immersed after a 30 min period of emersion. However, it returned to pre-emersion levels by the second hour of re-immersion. Daily rhythm resulted in a significantly higher nocturnal TAN excretion rate for J. edwardsii; no daily rhythm was observed for P. cygnus. Feeding had the largest influence on TAN excretion, with maximum increases of 6.28 (J. edwardsii) and 5.60 (P. cygnus) times the pre-feeding level. TAN excretion rates remained significantly higher than the pre-feeding levels for an extended period (26 h, J. edwardsii; 30 h, P. cygnus). Implications for the use of purging tanks in lobster holding facilities and for the design of biofiltration systems are discussed.     

Comparison of growth,digestive system maturation and skeletal development in sea bass larvae reared in an intensive or a mesocosm system

The quality of development in intensive or mesocosm hatchery‐reared Dicentrarchus labrax larvae was investigated using physiological indicators assessing ontogeny. Larvae were reared in intensive (120 L tanks) and in mesocosm systems (20 m³ enclosures) with the same feeding sequence, excluding the wild zooplankton naturally available in mesocosms. Faster growth was recorded since early development [16 day after hatching (DAH)] in the mesocosm. Maturation of the digestive system also occurred earlier as indicated by the higher amylase secretion ratios, the intestinal maturation index (alkaline phosphatase/leucine–alanine peptidase and aminopeptidase‐N/leucine–alanine peptidase ratios) and the more developed intestinal epithelium at 23 DAH. Nevertheless, the delay in digestive maturation in the intensive system seemed retrieved within few days. In both the groups, the number of vertebrae ranged between 24 and 26, with the dominant class being 25 vertebrae. However, the distributions differed between treatments for meristic characteristics, ossification stages and incidence of malformation types. Loss of a vertebra was more frequent in the intensive system, while the appearance of an additional vertebra was more frequent in the mesocosm. Ossification at 37 DAH was also more advanced in the mesocosm in addition to a lesser rate and severity of skeletal malformations. It is suggested that the early nutritional contribution of mesocosm wild zooplankton, yet at densities of 0.2–0.7 prey mL^?1, had key effects on larvae development since the early stages.     

Effects of microbial products and extra carbon on water quality and bacterial community in a fish polyculture system

A 55‐day mesocosm experiment was conducted to evaluate the effects of commercial microbial products (Novozymes Pond Protect and Novozymes Pond Plus) and extra carbon (glucose) on water quality and bacterial community in a fish polyculture system. A 2 × 2 layout, including four treatments (non‐supplementation of the microbial products or glucose, adding glucose, adding the microbial products and adding the microbial products and glucose in combination), was established. The microbial products and glucose were added on the 40th day, 46th day and 52th day. Ammonia, nitrite and nitrate reduced in the tanks after glucose addition, while adding the microbial products did not significantly affect ammonia, nitrite, nitrate, reactive phosphate, total nitrogen, total phosphorus, chemical oxygen demand and total organic carbon. Adding the microbial products and glucose affected relative abundance of some bacterial taxa, but did not reshape bacterial community. Non‐positive interactive effect on water quality and bacterial community was detected between the microbial products and glucose. This study reveals that supplementation of the microbial products did not benefit water quality in the fish polyculture system, and glucose addition could reduce ammonia, nitrite and nitrate.     

Effects of body weight, water temperature and ration size on ammonia excretion by the areolated grouper (Epinephelus areolatus) and mangrove snapper (Lutjanus argentimaculatus)

The effects of body weight, water temperature and ration size on ammonia excretion rates of the areolated grouper Epinephelus areolatus and the mangrove snapper Lutjanus argentimaculatus were investigated. Under given experimental conditions, L. argentimaculatus had a higher weight-specific ammonia excretion rate than E. areolatus. Weight-specific ammonia excretion rates of fasted individuals of both species showed an inverse relationship with body weight (W, g wet wt.), but a positive relationship with water temperature (t, °C). The relationships for total ammonia nitrogen (TAN) were: E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=21.4·exp^0.11t·W^−0.43 (r²=0.919, n=60); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=121.5·exp^0.12t·W^−0.55 (r²=0.931, n=60). Following feeding, the weight-specific ammonia excretion rate of E. areolatus increased, peaked at 2 to 12 h (depending on temperature), and returned to pre-feeding levels within 24 h. A similar pattern was observed for L. argentimaculatus, with a peak of TAN excretion being found 6 to 12 h after feeding. Stepwise multiple regression analysis indicated that weight-specific TAN excretion rates of both species increased with increasing temperature and ration (R, percent body wt. d⁻¹): E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=22.8·t−28.8·R−378.2 (r²=0.832, n=24); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=22.9·t−25.4·R−216.4 (r²=0.611, n=24). The effect of body weight on weight-specific postprandial TAN excretion was not significant in either species (p>0.05). This study provides empirical data for estimating ammonia excretion of these two species under varying conditions. This has application for culture management.     

Using a macroalgae Ulva pertusa biofilter in a recirculating system for production of juvenile sea cucumber Apostichopus japonicus

A simple indoor recirculating system for production of juvenile sea cucumber (Apostichopus japonicus) was operated on a commercial scale for 90 days during winter. The system consists of three 70 m³ sea cucumber rearing tanks and one biofilter tank where macroalgae (Ulva pertusa) was used as a biofilter in order to reduce water requirements. Effluent from the sea cucumber tanks drained into the macroalgae biofilter tank and were then returned to the sea cucumber tanks by a discontinuous-flow recirculation system. Survival and growth rates in the sea cucumber culture tanks were similar to those in the control tank (with one water exchange per day). The survival rate averaged about 87%. The average body weight increased from 3.5 ± 0.3 g to 8.1 ± 0.8 g and total sea cucumber biomass production over the experimental period was 745 g m⁻² after initial stocking densities of 375 g m⁻². The growth rate of U. pertusa was 3.3% day⁻¹. U. pertusa was efficient in removing toxic ammonia and in maintaining the water quality within acceptable levels for sea cucumber culture; there were only small daily variations of temperature, pH and DO. The U. pertusa tank removed 68% of the TAN (total ammonia-nitrogen) and 26% of the orthophosphate from the sea cucumber culture effluent; the macroalgae biofilter removed ammonia at an average rate of 0.459 g N m⁻² day⁻¹. It would be efficient to use the U. pertusa biofilter in a recirculating system for production of A. japonicus juveniles in winter.     

Farming triploid oysters

Although the commercial benefits of triploidy have been evaluated in the Pacific oyster Crassostrea gigas (Thunberg, 1793), eastern oyster C. virginica (Gmelin, 1791), Sydney rock oyster Saccostrea glomerata (Gould, 1850) and European flat oyster Ostrea edulis (Linnaeus, 1750), so far this technique has only been commercialised for Pacific oysters.

Commercial production of triploids on the West Coast of North America began in 1985. Since then production of triploids has greatly increased and the use of tetraploid males to fertilise eggs from diploids to produce batches of 100% triploids has been developed. In 1999/2000, triploid Pacific oysters made up 30% of all Pacific oysters farmed on the West Coast of North America. Some hatcheries now use tetraploid males instead of chemical or physical stress to produce triploids. The rapid uptake of triploid and tetraploidy techniques has been facilitated by the almost total dependence that these oyster industries have on hatcheries for the supply of seed. This industry in the Pacific Northwest of the US and in British Columbia, Canada, would not have developed to its current size without hatchery seed supplies. Triploids are preferred over diploids in summer because diploids are less marketable when in spawning condition.

There was only limited interest in triploidy production in France until 1999, when IFREMER began to make sperm from tetraploids available to commercial hatcheries. In 1999/2000, only 10% to 20% of all the hatchery-supplied Pacific oyster spat were triploids, but with the use of sperm from tetraploid oysters, this could increase sharply.

Elsewhere around the world, the commercial uptake of triploid oysters has been slow to develop. However, in countries where the production of Pacific oysters is based on hatchery supply of seed, it is likely that with the use of tetraploid oysters, the farming of triploid oysters will increase in the near future.     

The effect of diet and photoperiod on ammonia efflux rates of the African catfish, Clarias gariepinus (Burchell, 1822)

Total ammonia efflux rates of the African catfish, Clarias gariepinus (Burchell), were measured under different combinations of photoperiod (LD 24:0. LD 0:24, LD 12:12) and feeding regime (50% protein diet, 41% protein diet and zero food). A time-dependent variation of ammonia efflux following feeding was observed, with postprandial excretion rates in the first 12 h being greater than those in the following 12 h. Ammonia efflux rates were directly related to the level of protein in the diet under all photoperiod conditions. Photoperiod had no effect on ammonia efflux rate, except in the LD 24:0-high protein diet group, which may indicate a stress response.     

Seasonal Changes in Water Quality in Commercial Channel Catfish Ponds in Mississippi

Selected water quality variables were measured at monthly intervals for 1 yr in 10 commercial channel catfish ponds in northwest Mississippi. Temporal changes in most variables appeared to be related to seasonal periodicity of phytoplankton abundance. Phytoplankton standing crops and total organic matter were highest in summer months when primary production was favored by warm water temperatures, high solar irradiance, and large inputs of nutrients resulting from high summer fish feed allowances. As day length, water temperature, and feed inputs decreased in autumn and winter, phytoplankton abundance and organic matter concentrations decreased. Seasonal changes in total nitrogen and total phosphorus concentrations were similar to phytoplankton abundance because much of the total nitrogen and phosphorus was contained within phytoplankton cells. Contrasting to the seasonal trend for total nitrogen, concentrations of dissolved inorganic nitrogen were lowest in the summer and highest in the cooler months. Rapid assimilation by phytoplankton served to maintain relatively low concentrations of dissolved inorganic nitrogen during the summer despite highest nitrogen loading rates during that period. Low water temperatures and generally less favorable conditions for phytoplankton growth decreased rates of nitrogen assimilation in the winter and ammonia, nitrite, and nitrate accumulated. Soluble reactive phosphorus concentrations were low throughout the year because physico-chemical processes, such as precipitation and adsorption to bottom muds acted to continually remove inorganic phosphorus from the water column.     

The effect of four microbial products on production performance and water quality in integrated culture of freshwater pearl mussel and fishes

An 80‐day mesocosm experiment was conducted to evaluate the effect of four commercial microbial products on production performance and water quality in integrated culture of freshwater pearl mussel Hyriopsis cumingii, grass carp, gibel carp, silver carp and bighead carp. Five treatments were tested. One treatment with non‐supplementation of microbial products served as control (C). In the other four treatments, Novozymes Pond Protect (NO), Bio‐Form BZT‐Water Reform (WR), Bacillus natto (BN) and Effective Microbes (EM) were added at the intervals of two weeks, respectively. Mussel yield declined in the tanks with supplementation of the microbial products. No significant differences were found in fish yield and chemical water quality among the treatments except total nitrogen (TN) was higher in tanks EM than in tanks C. Biomass of phytoplankton and Cyanophyta was higher in tanks NO, WR, BN and EM than in tanks C. Supplementation of the microbial products resulted in change in bacterial community in which Actinobacteria, Chlorobi, Verrucomicrobia and Proteobacteria dominated. Bacterial community in the tanks was significantly affected by TN, total phosphorus, chemical oxygen demand and Cyanophyta biomass. This study reveals that the function of these microbial products as probiotics is limited in H. cumingii farming.     

葡萄糖添加对太湖水体浮游植物生长的影响

为探索葡萄糖(碳源)添加对浮游植物生长的影响,于2015年7月30日—8月6日用太湖梅梁湾水体进行了碳、氮、磷的营养盐添加试验。试验设置3个处理,每个处理均添加相同水平的氮、磷营养盐,而碳添加质量浓度分别为0 mg/L(对照组)、51 mg/L(低碳组)和102 mg/L(高碳组)。结果显示,对照组与低碳组的叶绿素a(Chl-a)均显著高于高碳组(P0.05),3个处理间总悬浮颗粒物(TSS)质量浓度没有显著差异(P0.05);整体上,第1~8天和第6~8天,高碳组的硝酸盐氮(NO_3~--N)、活性磷(SRP)质量浓度的降低速率均是最高的,低碳组次之,对照组最慢(P0.05)。研究表明,葡萄糖添加控制了浮游植物生长,促进了水体中无机氮、磷质量浓度降低;但在添加葡萄糖的处理中,无机氮、磷质量浓度降低速度的加快并没有得到更高的浮游植物浓度。     

Ammonia distribution and excretion in fish

This paper reviews the literature concerning ammonia production, storage and excretion in fish. Ammonia is the end product of protein catabolism and is stored in the body of fish in high concentrations relative to basal excretion rates. Ammonia, if allowed to accumulate, is toxic and is converted to less toxic compounds or excreted. Like other weak acids and bases, ammonia is distributed between tissue compartments in relation to transmembrane pH gradients. NH₃ is generally equilibrated between compartments but NH₄ ⁺ is distributed according to pH. Ammonia is eliminated from the blood upon passage through the gills. The mechanisms of branchial ammonia excretion vary between different species of fish and different environments, and primarily involves NH₃ passive diffusion and NH₄ ⁺/Na⁺ exchange. Water chemistry near the gill surface may also be important to ammonia excretion, but a more accurate measurement of the NH₃ gradient across the gill epithelium is required before a more detailed analysis of NH₃ and NH₄ ⁺ excretion can be made.