Mariculture Ponds Research Articles

Dynamics of dissolved nutrients in the aquaculture shrimp ponds of the Min River estuary, China: Concentrations, fluxes and environmental loads

Dissolved inorganic nutrients (NO2−-N, NO3−-N, NH4+-N, and PO43−-P) play a critical role in the effective management of water quality and prevention of fish and shrimp diseases in aquaculture systems. In this study, dissolved inorganic nutrient concentrations in the water column and sediment porewater, and the fluxes across the sediment-water interface (SWI) were investigated in three intensive shrimp ponds with zero water exchange to examine nutrient cycling during the different growth stages of shrimps. Distinct changes in the dissolved inorganic nutrient concentrations in both the water column and sediment porewater were observed among the three growth stages. Average NO2−-N, NO3−-N, NH4+-N, and PO43−-P concentrations in the sediment porewater were 3.53, 2.81, 29.68, and 6.44 times higher, respectively, than those in the water column over the study period, indicating that the pond sediment acted as a net source of nutrients to the water column. This was further supported by the net release of nutrients from the sediments to the water column observed during the incubation experiment. Nutrient fluxes were dominated by NH4+-N, while NOx−-N (NO2−-N and NO3−-N) and PO43−-P fluxes remained low. The high rates of NH4+-N release from the sediment highlight the need of taking into account the biogeochemical role of sediments in mitigating the problem of water quality degradation in coastal shrimp ponds. Based on a total water surface area of mariculture ponds and a total mariculture production of 2.57×106ha and 2.30×109kg, respectively, we estimated conservatively that approximately 4.77×104tons of total nitrogen and 3.75×103tons of total phosphorus are being discharged annually from the mariculture ponds into the adjacent coastal zones across China. Results demonstrated the importance of aquaculture pond effluent as a major contributor of water pollution in the coastal areas of China, and called for actions to properly treat these effluents in alleviating the eutrophication problem in the Chinese coastal zones.

Marine periphyton biofilters in mariculture effluents: Nutrient uptake and biomass development

Cost of effluent treatment, water quality maintenance and feeds constitute most of aquaculture's operational costs, and influence its sustainability. The present study examined the effectiveness of periphyton for biofiltration of mariculture effluents. Marine periphyton was allowed to spontaneously develop on a plastic net substrate, in experimental bioreactors that were fed with effluents from fish mariculture ponds. Biomass development and nutrient uptake were followed over four seasons. Attention was given to the orientation and area of the net substrate, season and additional operational factors. The highest specific growth rate (SGR) of 27% day−1 was measured during the second week of periphyton growth in the summer. Mean daily periphyton production rates in the spring and autumn were 2.4 and 1.8g (ash-free dry weight) m−2day−1, respectively. The vertical orientation of the net substrate was overall advantageous over the horizontal orientation. Increasing the substrate area of vertically oriented nets in the biofilter increased the removal efficiency of total ammonia nitrogen (TAN) up to 80%, and allowed more biomass production in the biofilter. Multiple polynomial regression models suggest strong effect of biomass weight and effluent retention time on the removal efficiency of TAN and dissolved inorganic nitrogen (DIN). The removal rates of TAN and DIN in these experiments were between 0.11 and 1.2gNm−2 (substrate area) day−1 for periphyton at the age of 7 and 42days, respectively. Marine periphyton seems to be a simple, low cost and sustainable component, which can perform biofiltration/rehabilitation of water quality and potentially serve as feed for fish and shrimp.

Community Based Milkfish Farming in Tanzania

In the 1990s experimental integrated mariculture of finfish, shellfish and seaweeds in a flow through system was developed to investigate bio-filtration in the ponds. The project supported mainly by WIOMSA culminated in a stakeholders’ workshop in 2004 translating the results of the experiment to community based projects. The finfish tested were milkfish ( Chanos chanos ), rabbit fish ( Siganus canaliculatus and S. sutor ), mullet ( Mugil cephalus ) and Zanzibar tilapia ( Oreochromis urolepis hornorum ). Before the workshop there were 3 milkfish mariculture ponds in Tanzania one of which was established by IMS. Following the workshop, pond finfish mariculture took off in the coastal Tanzania. In 2006, the first commercial type farm at Bagamoyo produced 1 MT/ha/yr, earning the group 2000 USD. Ever since, finfish farming has spread to all coastal districts with the highest production of 7.5 MT/ha/yr at Ndumbwe Mtwara in 2011. In 2011, trials of tilapia acclimatization and farming in estuarine and full strength sea water were started where survival and growth rates of fry and fingerlings of 4 species of tilapia were tested.

Penggunaan Keong Bakau Telescopium sp (Gastropoda: Potamididae) dan Siput Bakau Cerithidea sp (Gastropoda: Potamididae) Sebagai Biofilter terhadap Limbah Budidaya Ikan Bandeng (Chanos chanos)

Mangrove snail Telescopium sp and Cerithidea sp are natural biofilter that able used to manage the changes in water quality caused by the culture sewage. This research aimed to analyze the utilization of Telescopium sp and Cerithidea sp as natural biofilter for re-improving water quality level from culture sewage in the laboratory scale. The outcome of this study was expected to be valuable information that mangrove gastropods not only as pests in mariculture ponds, but also able to use as natural biofilter in pond sewage management for recovering water quality level. This research was conducted from April to July 2016 in Hatchery and Aquaculture Technology Laboratory, Aquaculture Department, Agriculture Faculty, Malikussaleh University. Descriptive and quantitative methods used in this research including two treatment and three replications. Water quality such as turbidity, temperature, ammonia, nitrate, nitrite, orthophosphate, pH and dissolved oxygen measured periodically as research parameters. The result showed that the utilization of mangrove gastropod Telescopium sp and Cerithidea sp as natural biofilter was able to re-improving the water quality value such as pH, ammonia, nitrat, nitrit, orthophosphate and turbidity to the normal level. Meanwhile, the utilization of mangrove gastropods as natural biofilter does not gave any significant changes in the value of temperature, salinity and dissolved oxygen. Cerithidea sp also has better performance to reduce the water nutrient level in culture sewage compared than Telescopium sp. Keyword: mangrove gastropod, biofiltration, water quality, culture sewage

Effects of Mariculture and Solar-Salt Production on Sediment Microbial Community Structure in a Coastal Wetland

ABSTRACT Li, Y.; Wang, Y.; Xu, S.; Hu, B., and Wang, Z.-L., 2017. Effects of mariculture and solar-salt production on sediment microbial community structure in a coastal wetland. Mariculture and solar-salt production are two pervasive anthropogenic activities in worldwide coastal areas; however, their effects on sediment microbial biomass, community composition, and diversity have received less attention. Here, this question was investigated using the phospholipid fatty acids (PLFAs) analysis and 16S rRNA gene sequencing in Bohai Rim, northern China. Both mariculture and salt production increased bacterial (+135% and +84%), fungal (+45% and +20%), and total PLFAs contents (+72% and +39%) compared with intertidal wetlands. Furthermore, mariculture and salt production shifted microbial PLFAs compositions. The ratio of fungi:bacteria-PLFAs decreased in mariculture ponds (−40%) and salt fields (−37%) relative to the undisturbed wetland, and the ratio of Gram-positive:Gram-negative bacteria decreased in the sa...

Taxonomy and morphology of four "ophrys-related" scuticociliates (Protista, Ciliophora, Scuticociliata), with the description of a new genus, Paramesanophrys gen. nov.

Generally, “ophrys- related” scuticociliates belong to a specialised group of ciliated protozoa that may act as commensals or pathogens of fishes and crustaceans. In the present study, four “ophrys- taxa” scuticociliates, i.e., Paramesanophrys typica gen. et sp. nov., Mesanophrys carcini (Grolière & Léglise, 1977) Small & Lynn in Aescht, 2001, Metanophrys sinensis Song & Wilbert, 2000, and Metanophrys similis Song et al., 2002, were collected from Chinese coastal waters or mariculture ponds and investigated. Paramesanophrys gen. nov. is assigned to the family Orchitophryidae and differs from its other genera mainly by the position of the paroral membrane relative to membranelle 1–3, i.e., the membrane extends anteriorly to the posterior end of membranelle 3. The type species P. typica gen. et sp. nov., is defined by an elongated body with the posterior end depressed where the caudal cilium is located; 20 or 21 somatic kineties; double-rowed membranelle 1 with eight to ten basal bodies in each kinety; irregularly multi-rowed membranelle 2 and membranelle 3; scutica comprising c. seven or eight kinetosome pairs; a single macronuclear nodule; and marine habitat. The redescription of the three previously known species can be summarized as follows: 1) improved diagnosis is provided for Metanophrys sinensis Song & Wilbert, 2000 based on the original description and the present study; 2) some population-dependent characteristics of our new Mesanophrys carcini isolate are presented; 3) Metanophrys similis, collected from the South China Sea, resembles the original Qingdao population.

Carbon dioxide and methane fluxes from feeding and no-feeding mariculture ponds

The CO2 and CH4 fluxes at the water–air interface were measured in shrimp (Marsupenaeus japonicus) monoculture ponds (S) with feed supply and shrimp-sea cucumber (Apostichopus japonicus) polyculture ponds (SS) without feed supply. During farming seasons of the whole year, cumulated CO2–C fluxes were −5.69 g m−2 (S) and 11.23 g m−2 (SS), respectively. The cumulated CO2 emissions from S and SS did not differ significantly. The cumulated CH4–C emissions from S (0.57 g m−2) were significantly higher than those from SS (0.068 g m−2). S absorbed C from the atmosphere with a mean absorption rate of −5.12 g m−2, whereas SS emitted C to the atmosphere with a mean emission rate of 11.30 g m−2. Over 20-year horizon, the compressive global warming potentials (cGWPs) were 33.55 (S) and 47.71 (SS), respectively, indicating both feeding and no-feeding mariculture ponds could promote global warming.

Simultaneous determination of 23-antibiotics in mariculture water using solid-phase extraction and high performance liquid chromatography-tandem mass spectrometry

A method for the determination of 23 antibiotics from 6 categories in water was developed by using solid-phase extraction and high performance liquid chromatography-tandem mass spectrometry (SPE-HPLC-MS/MS). Water samples were enriched and cleaned-up by solid-phase extraction cartridges. The MS detection parameters of the analyzed antibiotics, the pH values of loading buffers and the volumes of the eluents were optimized by comparing the sample recoveries under different conditions. All antibiotics were separated by gradient elution with the mobile phases of 0.1% (v/v) formic acid and 1 g/L ammonium formate in water and aceto-nitrile-methanol (1:1, v/v) mixture. The eluate was then analyzed by HPLC-MS/MS in both positive and negative electrospray ionization conditions with multiple reaction monitoring (MRM) mode. The method detection limits (MDLs) were in the range of 0.1-2.9 ng/L and the recoveries of 23 antibiotics in water ranged from 47.3% to 132.6%. The developed method was applied to the analysis of 5 water samples from mariculture ponds located in Dongying City, Shandong Province. The results showed that the antibiotics could be detected in all water samples. The trimethoprim showed the highest detection rate, and the florfenicol had the highest mass concentration which reached 261. 0 ng/L. The results showed that the developed method is efficient, sensitive and reliable, which is suitable for the detection of antibiotics in seawater samples.

Assessing mariculture water quality with the structural and functional characteristics of a ciliate community

Ciliated protozoa play important roles in micro-ecosystems, especially in marine biotopes. However, few studies have been carried out on the periphytic, or aufwuch, forms in mariculture waters so far. In this study, we sampled periphytic ciliate communities in two closed mariculture ponds (ponds CP1 and CP2) and a natural seawater reservoir (pond RP) using a glass slide method to evaluate their colonizing processes and general ecological features, as well as their application as water quality indicators. We analyzed species compositions, structural parameters (species number, richness, diversity, evenness, abundance and dBP) and functional parameters (G, Seq and T90%). Pond RP was characterized by higher levels of structural parameters (except for abundance and dBP) and more equal proportion of the major taxonomic groups. The values of Seq were significantly higher in pond RP and similar in both pond CP1 and CP2. It was also demonstrated that environmental factors, including NO2-H, NO3-H, NH3-H, soluble reactive phosphate, temperature and pH, were the first principal factors affecting the communities. Among them, temperature and chemical factors were all significantly and negatively correlated with species number (P<0.01), richness (P<0.01), diversity (P<0.01), and positive correlated with abundance (P<0.01). Opposite correlations between pH and structural parameters were observed. This study showed that there were significant differences in species composition, structural parameters and functional parameters of the periphytic ciliate communities among the ponds, which were in agreement with the water quality. Results of this study confirmed the periphytic ciliate communities to be useful bioindicators of water quality in intensive mariculture waters.

Bacterial diversity in various coastal mariculture ponds in Southeast China and in diseased eels as revealed by culture and culture-independent molecular techniques

NSFC [40632013, 40521003, 30900045]; MOST [200805068]; State Key Laboratory of Marine Environmental Science (Xiamen University) [MEL0701]; Natural Science Foundation of Guangdong Province, China [B09292]

Temporal population dynamics of dinoflagellate Prorocentrum minimum in a semi-enclosed mariculture pond and its relationship to environmental factors and protozoan grazers

The ecological processes and interrelationships between protists, either autotrophic or heterotrophic, and environmental factors in mariculture ponds are largely unknown. This study investigated the temporal dynamics of potentially harmful dinoflagellate, Prorocentrum minimum (Pavillard) Schiller, and its relationship to physico-chemical factors and protozoan grazers over a complete cycle in a semi-enclosed shrimp-farming pond near Qingdao, Northern China. P. minimum occurred frequently in low numbers from June to August, followed by a sharp increase from the middle of August, reaching a single maximum peak value of 2.2×105 cells L−1 in October. Temporal variation in abundance was positively correlated with dissolved nitrogen, but showed a significant inverse relationship to abundance of the dominant ciliates, Tintinnopsis lohmanni and Askenasia stellaris. The results provide statistical evidence that the number of P. minimum increased with increasing nitrogen, and the suppression or shortening of algal bloom may be associated with protozoan grazers, such as Tintinnopsis lohmanni, in mariculture ponds.

Colonization of periphytic ciliated protozoa on an artificial substrate in mariculture waters with notes on responses to environmental factors

Colonization of periphytic ciliates and their usefulness for monitoring water quality were evaluated using the glass slide method in two enclosed mariculture ponds used to culture crab larva and in a natural seawater reservoir. The results revealed that (1) the ciliate species composition and colonizing process differed between the culturing ponds and the natural reservoir and (2) the dominant ciliate species showed a greater distribution in terms of both the abundance and the occurrence frequency. This study also demonstrated that structural parameters were strongly related to water conditions. For example, the abundance was positively associated with NO 3 - – N and soluble reactive phosphate ( P < 0.05), whereas the species number, species diversity and evenness were negatively correlated with nutrients (e.g. NO 3 - – N and NH 3–N) and temperature ( P < 0.05). These findings support the evidence that periphytic ciliates are useful bioindicators of water quality in enclosed mariculture ecosystems.

Comparison of bacterioplankton communities in three mariculture ponds farming different commercial animals in subtropical Chinese coast

In order to explore the responses of the bacterioplankton community to different types of aquaculture environments, three mariculture ponds comprised of groupers (Epinephelus diacanthus, ED), prawns (Penaeus vannamei, PV), and abalone (Haliotis diversicolor supertexta, HDS) in southeast, coastal China were investigated. The free-living bacterial diversity was analyzed through the construction of 16S rDNA clone library. A total of 203 16S rDNA sequences from three clone libraries were classified into 118 operational taxonomic units (OTUs), of which 51, 31, and 42 OTUs were distributed in the ED, PV, and HDS pond, respectively, with Bacteroidetes (30.6%), Actinobacteria (55.2%), and Cyanobacteria (32.8%) as the dominant division in the respective ponds. Meanwhile, each pond occupied some unique OTUs that were affiliated with uncommon (sub-)phyla, such as candidate OP11 division, Acidobacteria, Deltaproteobacteria, Planctomycetes, and Verrucomicrobia. Bacterial diversity in the ED pond was the richest, followed by the HDS and the PV pond. OTUs of 61.9% and 94.9% have less than 90% and 97% similarity to their nearest neighbors in public databases, respectively. All OTUs were grouped into 67 clusters, covering 11 (sub-)phyla. The OTUs only from single pond distributed in 53 clusters (79.1%), the OTUs shared by two ponds were affiliated with 14 clusters (20.9%), and none of clusters was formed by the OTUs which commonly originated from the three pond libraries, suggesting that the composition of bacterial populations in these ponds were significantly different. These results indicate that the aquatic environment created by different mariculture animals may foster very special and complex bacterial communities.

Taxonomic studies on three marine pleurostomatid ciliates, Litonotus bergeri nov. spec., L. blattereri nov. spec. and L. petzi nov. spec. (Ciliophora, Pleurostomatida) from North China Sea

The morphology and infraciliature of three pleurostomatid ciliates, Litonotus bergeri nov. spec., L. blattereri nov. spec. and L. petzi nov. spec., collected from mariculture ponds near Qingdao (Tsingtao), China, were investigated using live observations and the protargol impregnation method. These new species are distinguished from their congeners by a combination of characters including the typical distribution of extrusomes, i.e., along entire ventral margin, the number of macronuclear nodules, features and number of somatic kineties, living morphology, number and position of contractile vacuoles and their marine biotopes. Considering the distribution of extrusomes and general morphology, five new combinations are suggested, Litonotus vermiforme (Sauerbrey, 1928) nov. comb. [basionym: Loxophyllum vermiforme Sauerbrey, 1928], Litonotus levigatum (Sauerbrey, 1928) nov. comb. [basionym: Loxophyllum levigatum Sauerbrey, 1928], Litonotus undulatum (Sauerbrey, 1928) nov. comb. [basionym: Loxophyllum undulatum Sauerbrey, 1928], Loxophyllum pictus (Gruber, 1884) nov. comb. [basionym: Litonotus pictus Gruber, 1884] and Loxophyllum trichocystiferus (Foissner, 1984) nov. comb. [basionym: Litonotus trichocystiferus Foissner, 1984].

Water Quality Control for Intensive Shrimp Culture Ponds in Developing Countries Using Ammonia-Nitrogen Uptake by Seaweed

We studied the practical use of seaweed to remove inorganic nitrogen, especially ammonia-nitrogen, from the intensive shrimp culture ponds in developing countries. At first, we considered and experimentally evaluated the performance of ammonia-nitrogen uptake by seaweed in terms of parameters essential to the designing of intensive mariculture ponds. Based on the mechanism of ammonia-nitrogen uptake by seaweed, it was predicted that the ammonia-nitrogen concentration in the shrimp culture pond could be controlled by keeping it lower than a certain limit of value using a sufficient amount of seaweed with a condition that the rate of ammonia-nitrogen generation was constant. Experimental ammonia-nitrogen uptake runs confirmed this prediction and gave the parameters essential to design the culture pond with seaweed. Secondly, the control of the pond water quality for the practical shrimp culture batch was simulated by simple calculation based on the material balance of ammonia-nitrogen with parameters obtained from the experiments. The concentration of ammonia-nitrogen could be favorably controlled using seaweed in the practical batch and this method found to be feasible. Consequently, the water quality control using ammonia-nitrogen uptake by seaweed was proposed as a simple and convenient method appropriate for the intensive shrimp culture pond in developing countries.

Ammonia-Nitrogen Uptake by Seaweed for Water Quality Control in Intensive Mariculture Ponds

We applied seaweed to controlling the ammonia-nitrogen content in intensive shrimp aquaculture ponds in developing countries. Sterile Ulva sp. in Kanazawa Bay, Yokohama, Japan, was selected as model algae. The water content in the alga cells was almost the same as the previous result for Ulva lactuca. The rates of ammonia-nitrogen uptake by algae were measured under various conditions including tropical conditions, i.e., higher light flux density and temperature, to know the effects of these conditions. Sterile Ulva sp. could remove ammonia-nitrogen in culture medium effectively. The algae took up ammonia-nitrogen even under no light. Light enhanced assimilation of ammonia-nitrogen in the alga cell. The tropical condition enhanced ammonia-nitrogen uptake by the alga. The ammonia-nitrogen uptake rate decreased with an increasing ammonia-nitrogen content in the alga cell. Based on these experimental results, we studied the mechanism of ammonia-nitrogen uptake by algae in terms of a Michaelis–Menten model with an inhibitory effect. The ammonia-nitrogen uptake obeyed the Michaelis–Menten model with uncompetitive inhibition by the inhibitor working on the complex of ammonia-nitrogen and its carrier, and the ammonia-nitrogen content in an alga cell was positively related to the inhibitory effect on ammonia-nitrogen uptake. Consequently, the uptake by alga was proposed for controlling the ammonia-nitrogen content in shrimp aquaculture ponds in developing countries, and useful information for shrimp pond design was provided.

Water Quality Modeling in the Rio Chone Estuary

Abstract Water quality within the Rio Chone estuary, a seasonally inverse, tropical estuary, in Ecuador was characterized by modeling the distribution of biochemical oxygen demand (BOD) and dissolved inorganic nitrogen (DIN) within the water column. These two variables are modeled using modified advection-diffusion equations within a two-dimensional, laterally-averaged hydrodynamic model. The model includes sources of salt, BOD and DIN from shrimp mariculture ponds in the region surrounding the estuary. The model was successful in simulating seasonal concentrations in DIN and BOD over a range in source concentrations. Seasonal BOD measurements along the length of the estuary were coincident with dissolved oxygen concentrations in the estuary (high BOD generally corresponding to low dissolved oxygen). Results suggest that the citing of shrimp ponds near the head of the estuary should be avoided in order maintain estuarine water quality and to maximize production.

Two new marine pleurostomatid ciliates from China, Amphileptus gui nov. spec. and Amphileptus yuianus nov. spec. (Ciliophora, Pleurostomatida)

The morphology and infraciliature of two pleurostomatid ciliates, Amphileptus gui nov. spec. and A. yuianus nov. spec., collected from mariculture ponds near Qingdao (Tsingtao), China, were investigated using living observations and the protargol impregnation method. These new species are distinguished from their congeners by a combination of characters including their marine habitat and the presence of an apical group of densely packed extrusomes. Amphileptus gui nov. spec. differs from A. yuianus nov. spec. mainly in the number of contractile vacuoles (3–7 vs. 1), the shape of extrusomes (thin bar-like vs. clavate), and the number of left and right somatic kineties (7–11 and 37–50 vs. 4 and 18–22).

Observations of pond hydrodynamics

This paper provides a detailed observation of pond hydrodynamics. Bathymetry and aerator deployment largely control the hydrodynamic regime. Aerators drive pond circulation, which is resisted by bottom and bank friction. Hydrodynamic friction is characterized by sediment grain size. One particular pond is offered as a proxy representative of Australian mariculture ponds in general: Pond X. The pond had been stocked with P. monodon at densities in the range 25–35 m −2 about ten times during the period from 1989 to 1995. Observations were made in the year 1996. The site was on the east coast of Australia at 18° south latitude. The location was sheltered by a mountainous offshore island, such that winds effecting the pond averaged 2.3 m s −1. Water exchange occurred at a rate of about 8.3% of pond capacity per day. Pond X was found to be rectangular, 120 m long and 87 m wide. The banks were found to slope between 1:1.5 and 1:7.6, with an average slope near 1:3. The pond was shallowest in one corner, where depth was 834 mm, and drained diagonally with 1872-mm maximum water depth. Aeration was provided by a total of six 1.5-kW machines, comprised of two of the paddlewheel type and four of the propeller-aspirator type. Each machine was found to deliver 200 N of horizontal thrust into the pond water column. The combined effect of the aerators created a circulation current averaging about 11 cm s −1 around the pond periphery. The central region of the pond was found to have a fluctuating velocity of less than 1 cm s −1. The mass-average size of pond soil and sediment was found to vary from 25 μm in the central region to 250 μm at the banks and where the bottom was swept by paddlewheels.

Benthic shear stress and sediment condition

This article presents a literature review and analysis which finds that the conditions in a shallow waterway are dependent on the underlying shear stress. Circulation and mixing have been recognised as somehow important to the health of the lower water column and sediment of a pond. Benthic shear stress is identified as one of the principal governors of sediment condition. Benthic shear stress regulates the convection of volatile substances such as oxygen across the sediment–water interface. Benthic shear stress is the primary determinant of where particulate matter scours, rolls, saltates, settles, and consolidates. The critical shear stress of very small particles tends to be determined by density rather than size. Excessive shear stress may cause organic material to become buried under a fallout of silt in locations with lower shear stress. Such organic matter trapped in a sludge blanket consumes oxygen faster than it can diffuse through the pores between grains of soil, resulting in anaerobic soils. The objective of pond aeration and circulation systems should be to optimise conditions for the growth of cultured stock. Better management of the epi-benthic habitat of shrimp and prawns would concurrently reduce the use of energy and soil. The finding is that pond sediment condition may be assessed in terms of benthic shear stress. Control of benthic shear stress would enable resuspension and oxygenation of organic detritus without making the situation worse by intermixing organic matter with mineral soil. Desirable benthic shear stresses are expected to exist in the range of 0.003–0.03 N/m 2 where organic matter is gently maintained in an aerobic state. Locations having less than 0.001 N/m 2 benthic shear stress are subject to burial under accumulating mineral silts. Excessive scour occurs in locations having more than 0.1 N/m 2. High stress locations are the source of suspended solids which fallout on locations experiencing lower rates of benthic shear stress. The declining productivity of shrimp mariculture ponds is associated with excessive stocking and feeding because these practices necessitate intensive aeration, which results in high rates of pond circulation. The circulation causes soil to be scoured in some places while fallout covers the bottom in other places. Consequently intensive cropping of a pond causes feed pellets and other organic material to be buried in the soil, creating anaerobic conditions whereby bacterial metabolites are produced and released into the water column.