Acute Toxicity of Copper Sulfate and Chelated Copper to Channel Catfish Ictalurus punctatus

Channel catfish fingerlings Ictalurus punctatus were exposed to copper sulfate or a commercial chelated copper product in a series of static toxicity tests conducted using waters with a wide range of total alkalinity and hardness values. Estimates of mean 96 h LC50 values were 0.05, 0.73, 0.95, and 0.98 mg/L as Cu for copper sulfate and 0.06, 1.51, 1.97, and 1.74 mg/L as Cu for the chelated copper product in waters having total alkalinities of 16, 76, 127, and 240 mg/L CaCO₃ respectively. On a copper basis, the chelated product was significantly ( P < 0.05) less toxic to fish than copper sulfate in all waters except that of the lowest total alkalinity. Highly significant ( P < 0.01) linear relationships were found between LC50 values for copper from copper sulfate and pH, log [total alkalinity], and log [total hardness], of test waters. These results cast doubt on the validity of the formula commonly used to calculate practical copper sulfate pond treatment rates, which is based upon a simple linear relationship between application rate and total alkalinity.     

Biochemical Oxygen Demand in Channel Catfish Ictalurus punctatus Pond Waters

A study of the biochemical oxygen demand (BOD) of waters from ten channel catfish ponds at Auburn, Alabama, revealed that the 5-d BOD (BOD₅) seldom exceeded 8 mg/L and that the ultimate BOD (BOD_u) was usually less than 30 mg/L. Water samples from catfish ponds usually needed to be diluted only 2 or 3 times to permit BOD₅ measurements, and nitrification occurred even during a 5-d incubation period. Catfish pond waters were not extremely high in ammonia nitrogen concentration, and ammonia nitrogen introduced in the ammonium chloride-enriched dilution water caused an appreciable increase in BOD of some samples. Plankton respiration is a major component of carbonaceous BOD (CBOD) in catfish pond waters. Thus, the BOD is not expressed as rapidly during 5-d incubations as in typical waste-water. The ultimate BOD (BOD_u) would be a good measurement of oxygen demand for catfish pond effluents, but it is difficult to measure. Data from this study suggest that BOD_u can be estimated from BOD₅, but the correlation is not strong ( R ²= 0.62). An alternative is to develop a short-term BOD measurement specifically for effluents from channel catfish and other aquaculture ponds. This study suggests that a 10-d BOD conducted without nitrification inhibition or addition of ammonia nitrogen in dilution water might be a better alternative to standard BOD₅ or BOD_u measurements normally used in wastewater evaluation.     

Impact of Copper Sulfate on Plankton in Channel Catfish Nursery Ponds

Many fish culturists are interested in applying copper sulfate pentahydrate (CSP) to channel catfish, Ictalurus punctatus, nursery ponds as a prophylactic treatment for trematode infection and proliferative gill disease by killing snails and Dero sp., respectively, before stocking fry. However, copper is an algaecide and may adversely affect phytoplankton and zooplankton populations. We evaluated the effects of prophylactic use of copper sulfate in catfish nursery ponds on water quality and phytoplankton and zooplankton populations. In 2006, treatments of 0 mg/L CSP, 3 mg/L CSP (0.77 mg/L Cu), and 6 mg/L CSP (1.54 mg/L Cu) were randomly assigned to 0.04‐ha ponds. In 2007, only treatments of 0 and 3 mg/L CSP were randomly assigned to the 16 ponds. Ponds treated with CSP had significantly higher pH and significantly lower total ammonia concentrations. Treatment of both CSP rates increased total algal concentrations but reduced desirable zooplankton groups for catfish culture. CSP has been shown to be effective in reducing snail populations at the rate used in this study. CSP treatment also appears to be beneficial to the algal bloom, shifting the algal population to green algae and increasing total algal biomass within 1 wk after CSP treatment. Although zooplankton populations were adversely affected, populations of important zooplankton to catfish fry began rebounding 6–12 d after CSP treatment. Therefore, if CSP is used to treat catfish fry ponds of similar water composition used in this study, fry should not be stocked for about 2 wk after CSP application to allow time for the desirable zooplankton densities to begin increasing.     

Slow‐release Coated Copper Sulfate as an Algicide for Aquaculture

A coated copper sulfate algicide designed for controlled release of copper was evaluated for its effectiveness in controlling phytoplankton in hybrid catfish, ♀Ictalurus punctatus × ♂Ictalurus furcatus, ponds. Copper concentrations were greater in ponds receiving weekly treatments with copper sulfate crystals than in ponds in which the coated copper sulfate was suspended in porous bags and left in ponds during the study. However, the coated copper sulfate treatment provided a similar degree of phytoplankton control for a period of about 4 mo. Copper additions did not negatively affect catfish survival, production, or feed conversion in either the copper sulfate crystal treatment or in the coated copper sulfate treatment as compared with the control (P > 0.05). Flavor scores for fish did not differ between control and treatments (P > 0.05). The coated copper sulfate appeared to be a potentially effective method for controlling phytoplankton in aquaculture ponds. It would be easier to apply and require fewer applications, and the coated copper algicide would not present a fish toxicity issue that can arise from high copper concentration immediately following copper sulfate crystal treatment.     

Acute Toxicity of Copper to Juvenile Freshwater Prawns,Macrobrachium rosenbergii

Abstract

Copper sulfate is an algicide that is commonly used for phytoplankton and filamentous algae control and has been used as a therapeutant in aquaculture. The objectives of this study were to determine the acute toxicity of copper sulfate and the safe level for use in freshwater prawn, Macrobrachium rosenbergii, production ponds in a high calcium and alkalinity environment. Six concentrations of copper sulfate (0, 0.2, 0.4, 0.6, 0.8, 1.0 mg/L) were tested in 8-L glass aquaria for 48 hours with three replicate aquaria per treatment. Concentrations of calcium hardness and alkalinity were set at 100 mg/L using calcium chloride and sodium bicarbonate, respectively. After 48 hours, survival of the control treatment (0% CuSO₄) averaged 97%, which was significantly higher (P< 0.05) than that of all other treatments. The survival in the 0.2 mg/L and 0.4 mg/L (70% and 73%, respectively) concentrations of CuSO₄ were significantly greater (P< 0.05) than higher dose treatments; but were not significantly different from each other (P> 0.05). Treatments containing 0.6, 0.8, and 1.0-mg/L copper sulfate demonstrated a dramatic decrease in prawn survival, which averaged 30, 7, and 0%, respectively. Regression analysis of the data predicted 48-hour LC₅₀ for copper sulfate tobe0.46 mg/L. Since recommended application rates for use of copper sulfate as an algicide are 1.0 mg/L or more for water with alkalinities of 100 mg/L, copper sulfate treatments are not recommended for prawn production ponds.     

Comparison of Copper Sulfate Concentrations to Control Ichthyophthiriasis in Fingerling Channel Catfish

ABSTRACT

Fingerling channel catfish Ictalurus punctatus were exposed to Ichthyophthirius multifiliis-infested fish until immature trophonts developed. The fish were transferred to individual static fiberglass tanks filled with 600 L of pond water (total alkalinity and total hardness was 220 mg/L and 101 mg/L, respectively) and were treated with 0, 1.1, 2.2, 3.3, or 4.4 mg/L copper sulfate (CuSO₄ · 5H₂O) every other day for four treatments to evaluate its effectiveness to control mortality associated with ichthyophthiriasis. Water temperature was maintained at 18 ± 1°C. Fish were observed for ten days post-treatment and mortalities were recorded. Results indicate that half of the recommended dose (1.1 mg/L CuSO₄) is needed to effectively control an occurrence of ichthyophthiriasis under the conditions of this study. However, fish culturists should be aware that effective CuSO₄ treatment of ichthyophthiriasis on channel catfish raised in ponds may be influenced by water chemistry characteristics and suspended materials such as pond sediments.     

Effects of Aeration, Alum Treatment, Liming, and Organic Matter Application on Phosphorus Exchange between Soil and Water in Aquaculture Ponds at Auburn, Alabama

Application of readily-oxidizable organic substrate to laboratory soil-water systems and fish ponds caused anaerobic conditions in bottom soil and water, and concentrations of soluble reactive phosphorus (SRP) increased. Aeration of ponds increased total phosphorus (TP) concentrations by suspending soil particles in the water, but SRP concentrations declined because of increased oxy- genation of bottom water and soil, Alum [Al₂(SO₄)₃·14H₂O] treatment of ponds reduced SRP and TP concentrations in ponds, but the low concentration of alum used, 20 mg/L, had little residual effect on phosphorus concentration. Application of agricultural limestone at 0.2 kg/m² to ponds with soil pH of 5.5 and Ca²⁺ concentration of 5 mg/L did not affect SRP and TP concentration. Unless pond soils were anaerobic at their surfaces, a condition not acceptable in thermally-unstratified fish ponds, soils released little phosphorus to the water. Strong adsorption of phosphorus by soils in intensive ponds with feeding is beneficial, because removal of phosphorus by aerobic soils is a control on excessive phytoplankton growth. In fertilized ponds, phosphorus must be applied at frequent intervals to replace phosphorus removed from the water by soils.     

Species Sensitivity to Copper

Abstract

Channel catfish, Ictalurus punctatus (Rafinesque 1818), and sunshine bass, female white bass Morone chrysops (Rafinesque 1820) × male striped bass M. saxatilis (Walbaum 1792), juveniles (10 and 12 g, respectively) were exposed to copper sulfate (CuSO₄) in a series of static toxicity tests to observe species sensitivity. The water used in this study was 18.9°C filtered well water with initial pH of 8.71, and total alkalinity and total hardness of 224 and 110 mg/L, respectively. Estimates of mean 96-hour median lethal concentration (LC50) values were 1.75 mg/L Cu (6.89 mg/L CuSO₄) for channel catfish and 0.85 mg/ L Cu (3.35 mg/L CuSO₄) for sunshine bass; LC50 values were calculated using nominal CuSO₄ concentrations. These values differed significantly. This study demonstrates that sunshine bass juveniles are less tolerant of CuSO₄ than channel catfish fingerlings when exposed concurrently in waters from the same source.     

The Potential Use of Mangrove Forests as Nitrogen Sinks of Shrimp Aquaculture Pond Effluents: The Role of Denitrification

A generalized nitrogen budget was constructed to evaluate the potential role of mangrove sediments as a sink for dissolved inorganic nitrogen (DIN) in shrimp pond effluents. DIN concentrations were measured in pond effluents from three semi-intensive shrimp ponds along the Caribbean coast of Colombia between 1994–1995. Mean NH₄⁺ concentrations in the discharge water for all farms were significantly higher (67 × 12 μg/L) than in the adjacent estuaries (33 × 8 μg/L). Average NH₄⁺ concentrations in the pond discharge over all growout cycles were similar, representing an approximate doubling in relation to estuarine water concentrations. In contrast, NO₂^-+ NO₃^- concentrations were similar in both pond effluent and estuarine waters. Dissolved inorganic nitrogen loading of the ponds was similar. The estimated reduction of DIN in pond effluents by preliminary diversion of outflow to mangrove wetlands rather than directly to estuarine waters would be × 190 mg N/m² per d. Based on this nitrogen loss and depending upon the enrichment rate, between 0.04 to 0.12 ha of mangrove forest is required to completely remove the DIN load from effluents produced by a 1-ha pond.     

Environmental Assessment of Channel Catfish Ictalurus punctatus Farming in Alabama

An environmental assessment was made of Alabama channel catfish Ictalurus punctatus farming which is concentrated in the west‐central region of the state. There are about 10,000 ha of production ponds with 10.7% of the area for fry and fingerlings and 89.3% for food fish. Food fish production was about 40,800 tons in 1997. Watershed ponds filled by rainfall and runoff make up 76% of total pond area. Water levels in many of these ponds are maintained in dry weather with well water. The other ponds are embankment ponds supplied by well water. Harvest is primarily by seine‐through procedures and ponds are not drained frequently. The main points related to Alabama catfish farming and environment issues are as follows: 1) catfish farming in Alabama is conservative of water, and excluding storm overflow, about two pond volumes are intentionally discharged from each pond in 15 yr; 2) overflow from ponds following rains occurs mostly in winter and early spring when pond water quality is good and stream discharge volume is high; 3) total suspended solids concentrations in pond effluents were high, and the main sources of total suspended solids were erosion of embankments, pond bottoms, and discharge ditches; 4) concentrations of nitrogen and phosphorus in effluents were not high, but annual effluent loads of these two nutrients were greater than for typical row crops in Alabama; 5) ground water use by the industry is about 86,000 m³/d, but seepage from ponds returns water to aquifers; 6) there is little use of medicated feeds; 7) copper sulfate is used to control blue‐green algae and off‐flavor in ponds, but copper is rapidly lost from pond water; 8) although sodium chloride is applied to ponds to control nitrite toxicity, stream or ground water salinization has not resulted from this practice; 9) fertilizers are applied two or three times annually to fry and fingerling ponds and occasionally to grow‐out ponds; 10) hydrated lime is applied occasionally at 50 to 100 kg/ha but this does not cause high pH in pond waters or effluents; 11) accumulated sediment removed from pond bottoms is used to repair embankments and not discarded outside ponds; 12) sampling above and below catfish pond outfalls on eight streams revealed few differences in stream water quality; 13) electricity used for pumping water and mechanical aeration is only 0.90 kW h/kg of production; 14) each metric ton of fish meal used in feeds yields about 10 tons of dressed catfish. Reduction in effluent volume through water reuse and effluent treatment in settling basins or wetlands does not appear feasible on most farms. However, some management practices are recommended for reducing the volume and improving the quality of channel catfish pond effluents.     

Dry-Tilling of Pond Bottoms and Calcium Sulfate Treatment for Water Quality Improvement

Three different pond bottom treatments were evaluated in 12 earthen ponds. Bottoms of four ponds on the Auburn University Fisheries Research Unit, Auburn, Alabama, were dried for 1 mo and tilled with a roto-tiller (dry-till treatment). Four other ponds were dried and tilled, and after filling with water, enough gypsum (calcium sulfate) was applied to give a total hardness of about 200 mg/L. Gypsum was reapplied as needed to maintain the hardness (dry-till with gypsum treatment). Four ponds were not subjected to bottom drying, tilling or gypsum treatment (controls). Channel catfish Ictalurus punctatus fingerings were stocked at 15,000/ha. Selected water quality variables were measured at 1- to 2-wk intervals during the growing season. Concentrations of most variables increased over time because feeding rate was increased progressively as fish grew. Compared to the controls, both treatments had lower concentrations of total phosphorus and soluble reactive phosphorus, and higher concentrations of dissolved oxygen ( P < 0.05). In addition, ponds of the dry-till with gypsum treatment had in addition lower concentrations ( P < 0.05) of chlorophyll a , chemical oxygen demand, gross primary productivity, and total alkalinity than control ponds. The reduction in chlorophyll a concentration suggested less phytoplankton in gypsum-treated ponds, and this effect was probably related to lower phosphorus availability because of calcium phosphate formation. Secchi disk visibility, total suspended solids concentrations, and turbidity did not differ significantly among the treatments ( P < 0.05). Total fish production and survival rate did not differ significantly ( P < 0.05) among the treatments. These findings suggest that water quality improvement can be achieved by drying and tilling pond bottoms between crops, and benefits possibly may be increased by treating low hardness waters with gypsum.     

Hemolymph Oxyhemocyanin and Protein Levels and Acid-Base Balance in the Tiger Shrimp Penaeus monodon Exposed to Copper Sulfate

Abstract.— Subadult tiger shrimp Penaeus monodon (30.15 ± 2.19 g) were exposed individually in sea water of 25%o to 0 (control), 1.11, 4.76, 10.06 and 19.09 mg/L copper for 24 h. Hemolymph pH, PO₂ (partial oxygen pressure), PCO₂ (partial carbon dioxide pressure), HCO₃, oxyhemocyanin and protein levels were determined. Hemolymph PO₂ increased, whereas hemolymph pH, PCO₂, HC0₃-, oxyhemocyanin. protein and the ratio of oxyhemocyanidprotein levels decreased with increasing concentrations of ambient copper in the range of 1.11 to 19.09 ma/L. It is concluded that P. monodon following 24-h exposure to ambient copper as low as 4.76 mg/L shows a reduction of oxyhemocyanin, protein, and the ratio of oxyhemocyanin to protein, and develops metabolic acidosis in the hemolymph.     

Acute Toxicity of Several Chemicals to the Oligochaete Dero digitata

Proliferative gill disease (PGD) is a serious problem in the farm-raised channel catfish Ictalurus punctatus industry. Interrupting the life cycle of the sporozoan causative agent by eliminating Dero digitata worms from culture ponds would be one method of controlling PGD. Eight chemicals—sodium chloride, hydrogen peroxide, formalin, potassium permanganate, liquid copper sulfate, chloramine-T, rotenone and Bayluscide—were tested for acute toxicity against D. digitata . Static, single compound acute toxicity tests were conducted using three replications (10 worm/replicate) of six chemical concentrations and a control. Spearman-Karber analysis was used to calculate 24- and 48-h LC50 concentrations based on active ingredient for each compound. Calculated 24-h LC50 values were: sodium chloride 6,800 mg/L, hydrogen peroxide 13.2 μL/L, formalin 23.3 μL/L, potassium perrnanganate 5.7 mg/L, copper sulfate 7.6 mg/L, chloramine-T 29.5 mg/L, rotenone 0.26 μL/L, and Bayluscide 0.24 mg/L. Formalin and hydrogen peroxide may be options for eliminating D. digitata populations in ponds with fish because their LC50 concentrations were consistent with safe concentrations for fish. Rotenone, Bayluscide, chloramine-T, formalin, and potassium permanganate may be useful as a pond sterilization strategy by treating fingerling ponds prior to stocking fish each year. However, the presence of substrate and organic matter in ponds could impact the efficacy of the chemicals and D. digitata's response to treatment. Treatments should be further evaluated to determine field efficacy, procedures for use, and effects on cost of production.     

Chlorination of Channel Catfish Ponds

Abstract— Laboratory studies with pond water samples revealed that 5 mg/L active chlorine was needed to provide enough chlorine residual to reduce biological activity. Treatment of channel catfish ponds with repeated, 0.1-mg/L doses of active chlorine from calcium hypochlorite at 6- to 8-d intervals, as sometimes done by catfish farmers, had little influence on water quality. Dissolved oxygen, total ammonia-nitrogen, and chlorophyll a concentrations and pH were similar between treated and control ponds. Concentrations of chemical oxygen demand and particulate organic matter were seldom different between treated and control ponds. Channel catfish survival and net production were not improved by chlorine treatment. Thus, chlorination of production ponds during the grow-out period is not a useful technique. Treatment of sediment samples from ponds with up to 1,200-mg active chlorinelkg soil did not reduce bacterial abundance, so chlorination of bottoms of empty ponds may not he an effective disinfection procedure. Chlorination of pond waters with 30-mg/L active chlorine caused complete kill of bacteria 24 h after treatment, although heterotrophic bacteria quickly re-populated the water. Thus, chlorination can be an effective way to disinfect ponds before stocking.     

A Practical Calcium Hardness Criterion for Channel Catfish Hatchery Water Supplies

Three pairs of brood channel catfish Ictalurus punctatus were induced to spawn in aquaria supplied with flowing water from a reservoir filled with ground water (calcium hardness = 110 mg/L as CaCO₃= 44 mg/L as calcium). Fertilized egg masses were allowed to incubate in aquaria for 6 h and each mass was then split into five portions. The five portions were then allowed to hatch and the resulting sac fry developed in waters with calcium hardnesses of 0, 1, 5, 10, or 100 mg/L as CaCO₃ (0, 0.4, 2, 4, or 40 mg/L as calcium). Test waters were prepared from distilleddeionized water and reagent-grade chemicals; tests were conducted using static-renewal conditions. Survival from hatch to onset of exogenous feeding ("swim-up") averaged 62% in calcium-free water and 98% at all other calcium hardness levels. Wet weight gain, dry weight loss, and resistance to environmental hypoxia were significantly affected ( P < 0.05) by environmental calcium levels: best growth, yolk utilization rate (indicated by changes in dry weight and visual observation), and tolerance to low dissolved oxygen concentrations were found at calcium hardnesses of 10 and 100 mg/L as CaCO₃. Based upon these results, a minimum calcium hardness of 10 mg/L as CaCO₃ (4 mg/L as calcium) is recommended for channel catfish hatchery water supplies.     

Acute Toxicity of 5% Non-Synergized Emulsifiable Rotenone to White River Crayfish Procambarus acutus acutus and White Perch Morone americana

Annual drawdown of crayfish culture ponds to plant forage crops also serves to eradicate most predaceous finfish. Without annual drawdown predaceous fish populations may reach numbers that can significantly reduce the crayfish crop. Frequent drawdown may not be feasible or desirable in some management schemes. Evidence in the literature suggests that differential toxicity of rotenone would allow removal of fish without harming crayfish in the same pond. In the current study, laboratory and in situ acute toxicity bioassays (96 h) were conducted with 5% non-synergized emulsifiable rotenone to define the maximum non-lethal concentration (LC₁₀₀) for white river crayfish Procambarus acutus acutus and the minimum lethal concentration (LC₁₀₀) for white perch Morone americana . Six concentration levels of rotenone formulation were tested in each of six toxicity trials with crayfish using dechlorinated tap water at 21–25 C. LC₀ (compensated for control mortality) was determined to be 3.0 mg/L. Significant crayfish mortality began at 4.0 mg/L. Acute toxicity to white perch was anticipated to be within recommended concentration levels on product label for similar fish, and was corroborated by laboratory bioassay (LC₁₀₀ of 0.15 mg/L). Both species were then tested together in laboratory aquaria utilizing pond water at room temperature. Concentration levels of 0.05–2.5 mg/L killed all white perch with no crayfish mortality. In the final phase of the study a 1.0 mg/L concentration of rotenone was applied to a pond containing both species held in cages. All white perch were dead within 24 h; no crayfish mortality was observed for the 96-h duration of the trial. It may therefore be possible to use this rotenone formulation to control white perch and other finfish in active crayfish culture ponds.     

Modeling industry-wide sediment oxygen demand and estimation of the contribution of sediment to total respiration in commercial channel catfish ponds

Data collected from 45 commercial channel catfish, Ictalurus punctatus, ponds were used to develop empirical models predicting sediment oxygen demand (SOD). Seven acceptable models were combined with a Monte-Carlo sampling distribution to predict industry-wide sediment oxygen demand (SOD_i). The SOD_i values obtained from the best equation were used in simulations to assess the effect of diurnally varying water column dissolved oxygen (DO) concentrations on SOD and the effect of pond water depth on the contribution of SOD to overall pond respiration. Estimated SOD_i ranged from 62 to 962 mg m⁻² h⁻¹, with a mean of 478 mg m⁻² h⁻¹. There was a 95% probability of mean SOD_i being ≥700 mg m⁻² h⁻¹. The effects of diurnal variation in DO concentration in the water column on expression of SOD was modeled by combining maximum SOD_i, an empirical relationship between DO and SOD, and simulated pond DO concentrations. At DO concentrations >15 mg l⁻¹, diel SOD in catfish ponds exceeded 20 g O₂ m⁻² day⁻¹. But when average diel DO was <4 mg l⁻¹ and the range of DO concentration was 6–8 mg l⁻¹, SOD decreased to 13 g O₂ m⁻² day⁻¹ because DO availability limited the full expression of potential SOD. Respiration totals for sediment (average SOD_i), plankton, and fish respiration were calculated for pond water depths ranging from 0.25 to 4 m. Although whole-pond respiration increases as pond depth increases, the proportion of total respiration represented by sediment decreased from 48 to 10% by increasing water depth over this range. The results of these studies show that SOD is a major component of total pond respiration and that certain management practices can affect the impact of SOD on pond oxygen budgets. Mixing ponds during daylight hours, either mechanically or by orienting ponds for maximum wind fetch, will increase oxygen supply to sediments, thereby allowing maximum expression of SOD and maximum mineralization of sediment organic matter. Given a mixed condition caused by wind or other artificial means, the construction of deeper ponds increases the total mass of DO available for all respiration, causing nighttime DO concentrations to decline at a slower rate, reducing the need for supplemental aeration. Because a pond’s water volume decreases over time from sediment accumulation, annual aeration costs will increase with pond age. Constructing ponds with greater initial depth will therefore reduce long-term cost of aeration, allow more flexible management of pond water budget, and reduce the long-term expense associated with pond reconstruction.     

Characteristics of Effluents from Central Arkansas Baitfish Ponds

Scientific information on baitfish effluents is important to provide a basis for the development of appropriate and cost-effective management practices that minimize environmental impacts. Effluents from 10 commercial golden shiner Notemigonus crysoleucas ponds in central Arkansas were sampled December 2000 through June 2001. Grab samples of the first and last 10% of pond volume were collected during intentional draining events. Effluents were sampled as they exited pond drainpipes and at the ends of drainage ditches just prior to stream discharge. Concurrent receiving stream samples were collected upstream and downstream of the discharge point. Total nitrogen (TN), total phosphorus (TP), 5-d biochemical oxygen demand (BOD_S), and total suspended solids (TSS) of each sample were measured. Mean whole effluent concentrations for the first 10% were 36 mg TSS/L, 9 mg/L BOD₅, 2 mg TN/L, and 0.5 mg TP/L. The water quality of the first and last 10% of pond effluent were not significantly different ( P < 0.05). Filtering effluents through a 5-pm mesh screen did not significantly reduce nutrient concentrations. Serial fractionation of effluents resulted in small but significant decreases in TSS concentrations in samples filtered through the 10, 8, and 5-μm meshes ( P < 0.05). Effluent discharge through farm ditches generally did not improve effluent water quality. Effluents collected at ditch ends were significantly less than drainpipe samples in BOD, concentrations only ( P < 0.05). Limited data on receiving stream water quality indicated that only TP concentrations were greater in pond effluents than in receiving streams. Overall, baitfish pond effluents are similar in composition to effluents of other phytoplankton-based pond production systems.     

Chemistry of Sediment Pore Water in Aquaculture Ponds Built on Clayey Ultisols at Auburn, Alabama

The composition of sediment pore water was determined for ponds constructed on clayey Ultisols at Auburn, Alabama. Pore water was anaerobic and contained much higher concentrations of ferrous iron (Fe²⁺), soluble reactive phosphorus (SRP), total phosphorus (TP), total ammonia-nitrogen (TAN), and sulfide (S²⁻) than surface or bottom waters. Concentrations of SRP and TP in pore water were higher in ponds with high soil phosphorus concentrations than in a new pond with less soil phosphorus. Increased concentrations of organic matter in soil or larger inputs of feed to ponds favored greater microbial activity in soils and higher concentrations of TAN in pore water. The pH of pore water was 6.5–7.0, and pH was apparently controlled by the equilibrium:

Movement of Fe²⁺, SRP, and S²⁻ from pore water into pond water apparently was prevented by the oxidized layer of soil just below the soil-water interface. Pond managers should concentrate on maintaining this oxidized layer to reduce the tendency for toxic substances to diffuse into the pond water.     

Water and Sediment Quality,Phytoplankton Communities,and Channel Catfish Production in Sodium Nitrate-Treated Ponds

Three channel catfish (Ictalurus punctatus) ponds were treated at two-week intervals with sodium nitrate at 2 mg NO₃ ^?-N/L per application and three ponds served as controls. Average concentration of nitrite-nitrogen measured midway between application dates never exceeded 1.2 mg/L in treated ponds, but on most sampling dates, nitrate concentrations were greater than those in control ponds (P < 0.1). Disappearance of nitrate-nitrogen from waters of treated ponds resulted primarily from nitrate reduction to free nitrogen gas. Soluble reactive and total phosphorus concentrations tended to be higher (P < 0.1) in treated ponds than in control ponds. There were no differences (P > 0.1) in pH and concentrations of total alkalinity, total ammonia nitrogen, and dissolved oxygen between treated and control ponds. The higher chlorophyll a concentration (P < 0.1) suggested that greater availability of nutrients in treated ponds resulted in more phytoplankton growth than in control ponds. Because of greater phytoplankton biomass, turbidity was higher and Secchi disk visibility less in treated ponds as compared to control ponds (P < 0.1). There were no obvious differences in phytoplankton community composition with respect to treatment—blue-green algae dominated the phytoplankton community in both treated and control ponds. Redox potential in sediment during crops was higher in ponds treated with sodium nitrate than in control ponds, indicating less anaerobic conditions. However, catfish survival, production, and feed conversion ratio did not differ (P > 0.1) between treatment and control.