Comparison of Organic and Inorganic Fertilizers for the Pond Production of Walleye,Stizostedion vitreum

ABSTRACT

Walleye were stocked at 20 fry/m³ and raised for 45-47 days in earthen ponds that were fertilized with organic or inorganic fertilizers. Organically fertilized ponds received periodic doses of alfalfa meal and torrula yeast. Nitrogen and phosphorus levels of 600 ug/L and 30 ug/L, respectively, were maintained by twice-weekly additions of liquid fertilizers in ponds of the inorganic treatment. Growth, survival, and production offish were not affected by the fertilizer treatment. The use of inorganic fertilizers is recommended for the pond production of walleye because it is easier and less costly than traditional methods involving the use of organic fertilizers.     

Preliminary Comparisons of the Native Penaeus setiferus and Pacific P. vannamei White Shrimp for Pond Culture in South Carolina, USA

Two pond experiments were conducted at the Waddell Mariculture Center to compare production characteristics of the native Penaeus setiferus and Pacific P. vannamei white shrimp in South Carolina. In 1985, 7–9 day old postlarval P. setiferus were stocked in one 0.1 and one 0.25 ha ponds, while P. vannamei of the same age were stocked in one 0.1 and one 0.25 ha ponds, while P. vannamei of the same age were stocked in one 0.1, one 0.25, and one 0.5 ha ponds. Both species were stocked at 12 shrimp/m². The shrimp were fed a 25% protein commercial food and harvested by draining after 147 d. Sarvival in all ponds was > go%, but growth and production of the P. setiferus were considerably lower than values obtained for P. vannamei: 12.8 g and 1,555 kg/ha/crop for P. satiferus versus 19.7 g and 2,477 kg/ha/crop for P. vannamei. In 1989, duplicate 0.1 ha ponds were stocked with P. setiferus and P. vannamei at 60 shrimp/m², and two additional 0.1 ha ponds were stocked with P. setiferus at 40/m². The P. setiferus postlarvae were produced at the Waddell Center from captive-reared and wild South Carolina brood stock. Rearing procedures involved paddlewheel aeration (10 hp/ha), regular water exchange (averaging 16–21%/d in all ponds), and use of a 40% protein feed. Due to the availability of postlarvae, the various treatments were stocked at different times. Both P. setiferus treatments were reared for 145 d, while the P. vannamei were reared for 165 d. P. setiferus at the 40/m² density attained mean size, survival, and standing crop biomass at harvest of 13.5 g, 97.5% and 5,259 kg/ha/crop, respectively. The 60/m²P. setiferus treatment was stocked 2 wk earlier and yielded 15.2 g mean weight, 87.5% survival, and 7,995 kg/ha/crop at harvest. The P. vannamei 60/m² treatment, which was stocked 3 wk earlier than any of the P. setiferus, produced mean size, survival and standing crop biomass at harvest of 17.1 g, 69.5% and 7,187 kg/ha/crop. Both survival and production levels would have been higher had not one replicate experienced a partial mortality due to a feeding accident. The 1989 study yielded what is thought to be the highest production levels yet achieved with P. setiferus in pond culture. These results suggest that P. setiferus may be a viable alternative to P. vannamei for intensive cultivation in the continental U.S. when P. vannamei are unavailable. Further evaluation of this potential is needed.     

Comparisons of Two By-Products and a Prepared Diet as Organic Fertilizers on Growth and Survival of Larval Paddlefish,Polyodon spathula,in Earthen Ponds

Two agro-industrial by-products, rice bran (RB) and distillers dried solubles (DS), and a prepared diet (PD) were evaluated as organic fertilizers for the production of juvenile paddlefish in nine 0.02-ha earthen ponds over a 40-day culture period. Paddlefish yield from ponds fertilized with RB (209 kg/ha) was significantly greater (P≤0.05) than that from ponds fertilized with DS (129 kg/ha), but it was not significantly greater than yields from ponds fertilized with PD (258 kg/ha). Fish survival from ponds fertilized with PD (79%) was significantly higher than from ponds fertilized with RB (55%) or DS (50%). There was no significant difference in survival between ponds fertilized with RB and DS. Secchi disk visibilities in ponds fertilized with RB were significantly lower than in ponds fertilized with DS and PD. Relatively low Secchi disk visibilities in RB-fertilized ponds were because of a brown stain or coloration which reduced sunlight penetrationa and growth of filamentous algai, not observed in Ds- or PD-fertilized ponds. Larvae congregated in areas where PD was being applied, whcih suggested direct feeding on PD. Paddlefish did not respond when RB and DS were applied to ponds. Cost per juvenile paddlefish raised in ponds fertilized with RB was $0.004, cheaper than $0.011 for fish raised in ponds fertilized with PD or DS. Rice bran is the recommended agro-industrial by-product to raise juvenile paddlefish greater than 120 mm total length based on improved fish yields, pond water quality, and lower cost per fish. The prepared diet may be used not only as an organic fertilizer, but also as a supplemental feed.     

Effect of using different types of organic animal manure on plankton abundance, and on growth and survival of Tilapia rendalli (Boulenger) in ponds

An experiment was conducted to evaluate the effect of using different types of organic manure on the plankton abundance, and growth and survival of Tilapia rendalli juveniles in ponds. Fish weighing 18.15±0.44 g were stocked into 12, 20 m² ponds at 2 fish m^?2 (40 fish pond^?1). There were three replicate ponds per treatment (chicken manure, cattle manure, pig manure, and no‐manure as a control). After 84 days the T. rendalli in the chicken manure treatment were significantly larger and had higher net annual yields than those in the cattle manure, pig manure and no‐manure treatments. The survival rates were not significantly different across the treatments. Significantly higher amounts of chlorophyll a and higher numbers of zooplankton were found in ponds fertilized with the chicken manure treatment. The overall results obtained in this study suggest that the use of chicken manure produces better results than cattle and pig manure treatments on unfertilized ponds.     

Design and Performance of a Horizontal,Axial-Flow Water Circulator

An axial-flow water circulator was developed for use in channel catfish, Ictalurus punctatus, culture ponds. The circulator design incorporated a series of 0.76-m diameter fan blades housed within a belled inlet duct 0.92 m in diameter and 1.22 m in length. Power was provided by a 2.24-kW gear motor. Power demand and discharge rates were established using all combinations of the following design variables: impeller type-three blades set at 30' angle or six blades set at 25' angle; impeller speed-90, 120, 144, and 180 rpm; number of impellers in series-1, 2, 3, or 4. The highest discharge rate of 63 m³/minute was established using four six-blade impellers operating at 144 rpm. A maximum discharge rate per unit of power input (efficiency) of 91.4 m³/minute-kW was obtained using two three-blade impellers operating at 90 rpm. Circulator efficiency decreased with increasing discharge rates as described by the model Y = 12888.8X^-1.68315, where Y = m³/minute-kW and X = m³/minute. Field tests conducted in 1.62-ha channel catfish production ponds demonstrated the ability of the circulator to increase water movement in all areas of the ponds and to reduce the frequency and total duration of required emergency aeration by 39.3% and 54.6%, respectively. Net production of channel catfish in ponds outfitted with the water circulator (6,683 kg/ha, n = 3) was not different (P > 0.05) than production in control ponds (6,205 kg/ha, n = 3).     

Influence of pond fertilization and feeding rate on growth performance, economic returns and water quality in a small-scale cage-cum-pond integrated system for production of Nile tilapia (Oreochromis niloticus L.)

The effects of pond fertilization and feeding rate on growth, economic returns and water quality were investigated to develop a low‐cost cage‐cum‐pond integrated system for production of Oreochromis niloticus (L.). Hand‐sexed male fingerlings averaging 19±0.39 and 32±0.69 g were stocked in cages and open ponds at 150 fish cage^?1 and 2 fish m^?2 respectively. Fish were cultured for 114 days in five triplicate treatments. Cages were installed into ponds and caged fish were fed a 24% protein diet at 3% (T1) and 6% (T2) body weight day^?1 (BWD) without pond fertilization, and 6% BWD with pond fertilization (T3). The open water in the fourth treatment (T4) was not stocked but contained caged fish, which were fed 6% BWD for the first 57 days followed by 3% BWD for the remaining period. Ponds in the control (T5) had no cages and were neither fertilized nor open‐pond fish fed. Feeding rate and pond fertilization significantly (P<0.05) affected fish growth, profitability and water quality among treatments. Fish growth, feed utilization, fish yield, water quality and profits were significantly (P<0.05) better in T3 than the other treatments. It was concluded that fish production and economic returns were optimized at 6% BWD in fertilized ponds.     

Fry Production of Shire River Tilapia Oreochromis shiranus at Two Broodstock Sex Ratios1

Abstract.— Shire River tilapia Oreochromis shiranus broodfish were stocked at a density of 1.25 fish/m² and sex ratios of either 1:1 or 1:3 (males: females). Two weeks after stocking, fry collection began. Fry were then harvested weekly for 9 wk with a fine-meshed dip net operated from the pond bank for 1.5 h each morning and afternoon. Ten weeks after fry collection began, all ponds were drained and completely harvested. Over the entire 84 d, fry production averaged 0.78 fry/m² per d and did not differ (P < 0.05) between treatments. Fry production per female was significantly higher (P < 0.02) in ponds stocked at a 1:1 sex ratio (111 fry/female) compared to a 1:3 sex ratio (66 fry/female). To avoid inbreeding without sacrificing production, a broodstock sex ratio of 1:1 can safely be used when producing O. shiranus fry at a density of 1.25 fsh/m² in earthen ponds. Competition among females is a possible cause of reduced fry production in densely-stocked brood ponds.     

Effects of Fertilization and of Fry Stocking Density on Pond Production of Fingerling Walleye,Stizostedion vitreum

The influence of fertilization and of fry stocking density on production of fingering walleye, Stizostedion vitreum, was evaluated in earthen ponds at North Platte State Fish Hatchery, North Platte, Nebraska. In 1990, five 0.4-ha ponds were fertilized with alfalfa pellets, and five were fertilized with soybean meal; four unfertilized ponds served as controls. All ponds were stocked with D2 (Dl = the day at hatch) walleye fry at 250.000ha. Differences in yield, number of fingerlings harvested, mean length, and mean weight amone treatments were not statistically significant (P> 0.05). In 691, two fertilization schedules (no fertilizer and fertilization with alfalfa pellets) and two fry stocking rates (250.000 and 375,000 fry/ha) were evaluated. Four ponds were used for each treatment. Statistically significant treatment differences were found in yield, number of fingerlings harvested/ha, average length, and average weight. Yield was higher in fertilized ponds compared with yield from unfertilized ponds at both stocking densities, but yield did not differ significantly between stocking density treatments given the same fertilizer treatment. Survival did not differ between density treatments, but total number of fish harvested was significantly greater from ponds stocked at the higher density. Fingerlings with the largest average weight were raised in fertilized ponds that were stocked at 250,00O/ha, while the smallest fingerlings were from unfertilized ponds that were stocked at 375,000ka. Days in culture interval, which varied among ponds by 9 days in 1990 and 10 days in 1991, was significantly correlated with most production variables in 1990 and with all production variables in 1991. Means of water quality variables were not significantly different between fertilized and unfertilized ponds in either year, but significant differences were found in means of three water quality variables between 1990 and 1991. Yield in both fertilized and unfertilized ponds in 1991 was less than in 1990.     

Significance of nitrogen fixation in fish ponds

The magnitude of nitrogen fixation in an inorganic fertilized and cereal fed system (fish pond) was measured by an in situ application of the acetylene reduction method. The effects of inorganic fertilization were intensively examined. In comparison with natural lakes, the fish ponds exhibited a relatively low fixation rate. The midday nitrogen fixation rate was usually less than 30 μg at N·m^?2·h^?1. The total income was equal to 5.7 kg N·ha^?1 or 0.575 g N·m^?2 for the growing season. Fish-induced bioperturbation and nitrogen fertilization, in the form of inorganic and organic fertilizers and foods, are considered to be the major regulatory factors in nitrogen fixation.     

Pond Production of Fingerling Walleye,Stizostedion vitreum,in the Northern Great Plains

The cultural practices used to produce fingerling walleye, Stizostedion vitreum, in drainable earthen ponds are described for a state fish hatchery in Nebraska and two federal hatcheries in North Dakota. The ponds were filled 1 to 7 days before D2-D4 (Dl=the day of hatch) walleye fry were stocked. At one hatchery, ponds were sometimes double-cropped, first for production of northern pike, Esoxlucius. The two federal hatcheries fertilized ponds with ground alfalfa hay or pellets, while the standard practice at the Nebraska hatchery was not to fertilize walleye ponds, because of concern that fertilization would result in weed problems and oxygen depletion. One hatchery seeded the ponds with rye grass in the fall. Two of the hatcheries regularly used herbicides to prevent the stranding of fingerlings during harvest and their mortality caused by entangment with net algae, Hydrodicton. When used, herbicide treatment was applied before ponds were filled (Aquazine^TM) or as needed during the culture interval (Aquazine^TM) or copper sulfate). Harvesting was done after 24 to 58 days; the extreme range represented variation among hatcheries; the variation among ponds at a given hatchery ranged from 4 to 10 days. Harvest occurred when fingerlings were 25 to 50 mm total length and weighed 1,500-5,440 fish/kg. Harvests ranged from 11,933 to 308,537 fingerlings/ha. Survival ranged from 3 to 104% of the estimated number of fry stocked.     

Production of the Malawi chambo, Oreochromis karongae (Trewavas, 1941) association, and Oreochromis shiranus (Boulenger, 1896) in polyculture with the African catfish, Clarias gariepinus (Burchell, 1822)

Results are reported of the growth and yield of the Malawi chambo, Oreochromis karongae (Trewavas, 1941) association, and Oreochromis shiranus (Boulenger. 1896) in polyculture with Clarias gariepinus (Burchell. 1822). Six ponds of 150 m² were assigned to two replicates of three treatments: C. gariepinus and O. shiranus; C. gariepinus and chambo spawned on station; C. gariepinus and chambo collected from the lake. Total fish stocking density was 3 m^?2, and stocking ratio 1:2 (C. gariepinus: titapias). Initial mean body weights were 10.9 g for O. shiranus. 13.2 g for C. gariepinus and 13.3 g for chambo. The ponds were fertilized with chicken manure at the rate of 13.5 kg dry matter ha^?1 day^?1, representing the daily NPK loading of 0.618.0.186 and 0.191 kg ha^?1, respectively. Maize bran was applied at 3% body weight day^?1 for 168 days. Fish growth rate for C. gariepinus was significantly higher (P < 0.05) than that of the tilapias. Weight gains were 0.48-0.57 g day^?1 for C. gariepinus, 0.30-0.31 g day^?1 for chambo and 0.24 g day^?1 for O shiranus. There was no difference (P > 0.05) in the growth of chambo despite the source of fingerlings. More fish biomass came from C. gariepinus stocked at 1 m^?2 than from the tilapias stocked at 2 m^?2. Extrapolated fish yields in the range of 4.37-4.75 t ha^?1 year^?1 were obtained from the polyculture of chambo and C. gariepinus. Oreochromis shiranus and C. gariepinus gave 3.95 t ha^?1 year^?1. Low water temperatures for 112 days slowed the growth of tilapias but did not seem to inhibit the growth of C. gariepinus. Chicken manure and maize bran, applied at smallholder farmer's level, has produced higher yields than by using O. shiranus in monoculture at optimal temperatures. The yields obtained show that the polyculture system is feasible during the cold season and may justify investment in aquaculture at semi-intensive level in Malawi.     

Role of organic fertilizers in walleye (Sander vitreus) production in plastic‐lined culture ponds

This study used six 0.04 ha plastic‐lined ponds to compare the effects of a fertilization regime using a one‐time initial application of an organic fertilizer (alfalfa pellets) with the current regime of weekly applications of organic fertilizers on the abundance and distribution of aquatic invertebrates and walleye, Sander vitreus, fingerling production. Walleye, 3–4 days post hatch, were stocked on 1 May 2002 and harvested on 6–7 June 2002. Throughout the growing season, a ratio of 7:1 total nitrate‐nitrogen to total phosphorus was maintained in all ponds regardless of the treatment. Once fry were stocked, ponds in Treatment #1 were fertilized weekly with organic fertilizer (alfalfa pellets; 112 kg ha^?1 week^?1) for a total of 795 kg ha^?1 pond^?1. Ponds in Treatment #2 only received an initial application of alfalfa pellets (112 kg ha^?1). Ponds in Treatment #1 had significantly higher ammonia and nitrate levels as well as higher chironomid larvae but not zooplankton compared with the other treatment. At harvest, walleye in the Treatment #1 ponds were significantly longer and heavier; however, the survival and relative weight were not significantly different. These results suggest that weekly applications of organics are important for the benthic food base and growth of fingerling walleye reared in plastic‐lined ponds.     

Intensification of Shrimp Culture in Earthen Ponds in South Carolina: Progress and Prospects

Experiments on the intensive cultivation of Pacific white shrimp, Penueus vunnumei, in ponds in South Carolina were begun in 1985 at the Waddell Mariculture Center. A preliminary study involved two 0.1 ha ponds stocked at an average of 43 postlarvae/m², with management practices based on those used in Taiwan for intensive pond culture of Penueus monodon. Harvest yields averaged 6,757 kg/ha for one crop, demonstrating the technical feasibility of such intensive culture of P. vannumei. In 1986, 2.5 ha of ponds at the Waddell Center (six ponds totaling 2.0 ha at 40 postlarvae/m² and two totaling 0.5 ha at 60/m²) yielded a total of 13,606 kg (5,442 ke/hn). These results were obtained even though aeration and water exchange rates were substanthlly reduced and South Carolina experienced its worst heat wave and drought. This served as a pilot-sde, proof-ofconcept test. Tank studies in 1985 and 1986 showed little effect of stocking density on shrimp growth rate at densities of 20–100 animals/m². This was confirmed in ponds in 1987 when no differences in growth rates were observed at densities of 20–100 postlarvae/m². Harvest biomass increased directly with stocking density in all trials, reaching a maximum of 12,680 kg/ha/crop at 100 shrimp/m² in 1987. Initial attempts to intensify production in the nascent South Carolina shrimp farming industry occurred in 1986, when approximately 32 ha of private ponds were stocked at densities of 10–32 postlarvae/m². Farm harvests increased with stocking density, with maximum yield of 3,656 kg/ ha/crop. This trend toward intensification in the private sector is continuing, and in 1987 maximum harvests from private ponds were 5,050 kg/ha from a 0.3 ha pond and 4,625 kg/ha from a 1.5 ha pond. Prospects for further implementation of intensive culture in the private sector appear excellent, with yields of ≥ 10,000 kg/ha/crop expected from private farms within the next few years.     

Nursery rearing of the Asian catfish, Clarias macrocephalus (Günther), at different stocking densities in cages suspended in tanks and ponds

Growth and survival of hatchery‐bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m^?3 in tanks and 114, 228 and 457 fry m^?3 in ponds. Fish were fed a formulated diet throughout the 28‐day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3–14.6% day^?1, than those in cages suspended in tanks (SGR range 9–11.3% day^?1). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m^?3 were similar to each other but were significantly lower than those of fish held at 114 m^?3. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m^?3 in tanks and at 114 m^?3 in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3–4 cm total length for stocking in grow‐out culture can still be attained at stocking densities of 457 m^?3 in nursery pond and 571 m^?3 in tanks.     

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.     

Cage‐pond integration of African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) with carps

Cage‐pond integration system is a new model for enhancing productivity of pond aquaculture system. A field trial was conducted using African catfish (Clarias gariepinus) and Nile tilapia (Oreochromis niloticus) in cages and carps in earthen ponds. There were four treatments replicated five times: (1) carps in ponds without cage, (2) tilapia at 30 fish m^?3 in cage and carps in open pond, (3) catfish at 100 fish m^?3 in cage and carps in open pond, (4) tilapia and catfish at 30 and 100 fish m^?3, respectively, in separate cages and carps in open pond. The carps were stocked at 1 fish m^?2. The cage occupied about 3% of the pond area. The caged tilapia and catfish were fed and the control ponds were fertilized. Results showed that the combined extrapolated net yield was significantly higher (P < 0.05) in the catfish, tilapia and carps integration system (9.4 ± 1.6 t ha^?1 year^?1) than in the carp polyculture (3.3 ± 0.7 t ha^?1 year^?1). The net return from the tilapia and carps (6860 US$ ha^?1 year^?1) and catfish, tilapia and carps integration systems (6668 US$ ha^?1 year^?1) was significantly higher than in the carp polyculture (1709 US$ ha^?1 year^?1) (P < 0.05). This experiment demonstrated that the cage‐pond integration of African catfish and Nile tilapia with carps is the best technology to increase production; whereas integration of tilapia and carp for profitability.     

Effects of stocking density and feeding duration in cage‐cum‐pond‐integrated system on growth performance,water quality and economic benefits of Labeo victorianus (Boulenger 1901) culture

We evaluated the effect of varying cage stocking density (60, 90 and 120 fish m^?3) and feeding duration (10, 30 and 60 min) in a cage‐cum‐pond‐integrated system on growth performance, water quality and economic benefits in Labeo victorianus culture. Interactions between stocking density and feeding duration significantly (P < 0.05) affected the fish growth performance and yields in the cages‐cum‐pond system. Stocking density of 60 fish m^?3 resulted in the highest growth in cages and in ponds regardless of the feeding duration, but produced lower yields than at stocking density 90 fish m^?3_. The lowest Apparent Food Conversion Ratio (AFCR) in cages occurred at stocking density of 60 fish m^?3 and feeding duration of 30 min. Growth performance in the open ponds declined with increased feeding duration of the caged fish. Survival in cages and in the open ponds decreased with increased cage density, but was not affected by feeding duration. Low dissolved oxygen were recorded, at stocking density of 120 fish m^?3, the lowest DO occurred when feeding of caged fish lasted 60 min. Growth performance, water quality and economic benefits in Labeo victorianus culture positively respond to interaction between stocking density and feeding durations.     

Effects of Pond Volume Manipulation on Production of Fingerling Largemouth Bass,Micropterus salmoides

Hatchery ponds were manipulated by timing of filling to increase the efficiency of production of fingerling largemouth bass, Micropterus salmoides. The effects on pond productivity of fertilizing with chicken manure versus plant meals (consisting of equal parts by weight of cottonseed meal, alfalfa meal, and wheat shorts) were also examined. When ponds were filled in stages, more favorable water temperatures for largemouth bass were achieved, and desirable dissolved oxygen concentrations were maintained. Chlorophyll a levels and plankton community respiration rates were higher in ponds that were fertilized with the plant meals than in ponds fertilized with chicken manure (25% dry matter). Secchi disk visibility was relatively greater in chicken manure ponds than in ponds fertilized with the plant meals; however all differences were not significant. Zooplankton densities were comparable among treatments. Filling ponds in stages had no significant effects on chlorophyll a, plankton community respiration rate, Secchi disk visibility, or zooplankton abundance and population dynamics. Daily production of largemouth bass was greater in ponds filled in stages and fertilized with plant meals than in other treatment ponds. Yield was highest in stage-filled ponds fertilized with plant meals and lowest in full ponds fertilized with chicken manure. Filling ponds in stages reduced the fertilizer cost per kilogram of largemouth bass by 50% in ponds fertilized with plant meals and by 65% in manure-fertilized ponds.     

Effects of Two Densities of Caged Monosex Nile Tilapia, Oreochromis niloticus, on Water Quality, Phytoplankton Populations, and Production When Polycultured with Macrobrachium rosenbergii in Temperate Ponds

The effects of different densities of caged Nile tilapia, Oreochromis niloticus, on water quality, phytoplankton populations, prawn, and total pond production were evaluated in freshwater prawn, Macrobrachium rosenbergii, production ponds. The experiment consisted of three treatments with three 0.04‐ha replicates each. All ponds were stocked with graded, nursed juvenile prawn (0.9 ± 0.6 g) at 69,000/ha. Control (CTL) ponds contained only prawns. Low‐density polyculture (LDP) ponds also contained two cages (1 m³; 100 fish/cage) of monosex male tilapia (115.6 ± 22 g), and high‐density polyculture (HDP) ponds had four cages. Total culture period was 106 d for tilapia and 114 d for prawn. Overall mean afternoon pH level was significantly lower (P ≤ 0.05) in polyculture ponds than in CTL ponds but did not differ (P > 0.05) between LDP and HDP. Phytoplankton biovolume was reduced in polyculture treatments. Tilapia in the LDP treatment had significantly higher (P ≤ 0.05) harvest weights than in the HDP treatment. Prawn weights were higher (P ≤ 0.05) in polyculture than prawn monoculture. These data indicate that a caged tilapia/freshwater prawn polyculture system may provide pH control while maximizing pond resources in temperate areas.     

Determination of dosage of Azotobacter and organic fertilizer for optimum nutrient release, net primary productivity and fish growth in fresh water fish ponds

Four experiments were conducted in order to determine the optimum dosageof Azotobacter chroococcum vis-a-vis organic fertilizer(cow-dung) required for optimum pond productivity. Hydrobiological parameters ofpond water, Azotobacter survival (viable counts), netprimary productivity (NPP) and fish growth were monitored. Studies have revealedthat irrespective of the treatments, dissolved oxygen (DO) levels weresignificantly (P < 0.05) lowered on inoculating the ponds withAzotobacter. Alkalinity, O-PO₄,NO₃-N, turbidity, NPP, plankton population and fish growth weresignificantly (P < 0.05) enhanced in ponds inoculated withAzotobacter @ 100.0 ml pond^–1w^–2 in combination with cow-dung @ 10000 kgha^–1 y^–1. At higher or lower dosages offertilizers, the values in most of these parameters remained low. On the otherhand, total kjeldahl nitrogen and NH₄-N increased continuously. Ingeneral, viable bacterial counts decreased with increase in pH, however, therate of nitrogen fixation was not affected. Multivariate analysis of the data revealed a significantpositive correlation of nutrients (Total kjeldahl Nitrogen, NO₃-N andO-PO₄), with NPP and plankton populations. NH₄-N, however,showed a significant negative correlation with DO, NPP and plankton populations.Highest fish biomass and SGR also coincided with the highest NPP and planktonpopulations, revealing that a dose of 100.0 ml pond^–1w^–2 (for 25 m³ ponds) ofAzotobacter along with 10000 kg ha^–1y^–1 of cow-dung appears to be optimum for obtainingoptimum pond productivity and fish yield. Nutrients in the sediment(NO₃-N and O-PO₄) also followed similar trend. On theother hand, organic carbon increased continuously with each increase in thedosage of fertilizers. A decline in fish biomass and pond productivity at higherfertilizer dosages has been attributed to low DO, high NH₄-N and BOD.