Natural Food Selectivity Changes with Weights of Nile Tilapia,Oreochromis niloticus (Linnaeus), Reared in Fertilized Earthen Ponds

This work was carried out to study the relationship between fish weight and natural food selectivity of Nile tilapia, Oreochromis niloticus (Linnaeus) reared in earthen ponds without supplementary diet and to guide the adaptation of feeding and fertilization strategies. Fish were stocked (1.5 fish/m²) in four fertilized earthen ponds (0.1 ha) for 6 months. Fifty fish were sampled monthly to estimate individual total weight and length and evaluate stomach contents. Fish specimens were categorized into different weight classes: <25 g, 25–50 g, 50–75 g, 75–100 g, and 100–125 g. Overall, the 50–75 g weight class had the highest degree of stomach fullness. The intestinal length-fish length ratio was similar across all fish weights, ranging from 2.9–3.4. Likewise, the composition of food items found in fish stomach was ranked as phytoplankton > detritus > zooplankton. Phytoplankton contribution to gut content increased with increasing fish weight, while detritus and zooplankton contribution decreased. Zooplankton never exceeded 1% of total stomach contents. Cyanobacteria, Chlorophyceae, Bacillariophyceae and Euglenophyceae mostly represented the phytoplankton. Bacillariophyceae dominated the phytoplanktonic portion of stomach contents at small fish size (<75 g/fish), while Chlorophyceae is the dominant group at large fish size (> 75 g/fish). Fish could select Cyanobacteria and Euglenophyceae at all fish weights, meanwhile Chlorophyceae and Bacillariophyceae were eaten with slight selectivity at larger weights..     

Feed preferences of Salminus brasiliensis (Pisces, Characidae) larvae in fish ponds

Feed preferences of dorado, Salminus brasiliensis, in the early stages of life was studied in larvae, stocked 5 days after hatching in three earthen commercial ponds (810 m², 900 m² and 1480 m²) at a density of 30 m^− 2. Larvae were fed on natural food from ponds supplemented with a commercial ration (40% crude protein), and for 12 days fish samples were taken daily in the morning and in the afternoon from each pond to analyze the food items present in the diet. Zooplankton available in the environment was also analyzed. Feeding was intensive since 94% of the larvae guts examined contained food. Since the commercial diet was not found in the dorado guts, the natural diet dominated the artificial food, but the cannibalistic behavior typically found in laboratory conditions was not observed. Insect larvae and cladocerans were the main prey items found in the gut of the larvae. In fish ponds dorado larvae can be considered a generalist feeder, since small amounts of different food items were consumed, but they tend to specialize in some items, according to their developmental stage.     

Diet composition of sturgeon fry (Acipenser persicus) reared in fertilized earthen ponds

Artificial rearing of fry has been introduced as an alternative to supply fry and juvenile sturgeon in order to restock the depleted sturgeon population in the Caspian Sea. The aim of this study is to assess the feed selection characteristics of sturgeon (Acipenser persicus) fry during the period in which they stay in earthen ponds before being released into the river. Sturgeon fry weighing around 150 mg were introduced into five almost similar‐sized earthen ponds. The ponds were enriched with fertilizer to supply natural food for the fries. A weekly sample of six specimens was collected from each pond during the 5 weeks of the experiment. All collected fish were weighed and then dissected for inspection of the stomach and the intestine content. The overall stomach content measured from 150 fish showed that around 74% of the stomach content was composed of chironomids and the rest was daphnia and cyclops. At the beginning of the study (first 2 weeks), sturgeon fry feed more on daphnia and cyclops; this trend, however, reversed in the last 2 weeks of the study. In conclusion, sturgeon fry feed on three prey groups—chironomids, daphnia and cyclops—during their lifespan in earthen pond. Feeding on chironomids larvae increased with sturgeon fry size.     

Grow-out of sandfish Holothuria scabra in ponds shows that co-culture with shrimp Litopenaeus stylirostris is not viable

We examined the potential for producing the large numbers of sandfish (Holothuria scabra) needed for restocking programmes by co-culturing juveniles with the shrimp Litopenaeus stylirostris in earthen ponds. Our experiments in hapas within shrimp ponds were designed to detect any deleterious effects of sandfish on shrimp, and vice versa. These experiments showed that a high stocking density of juvenile sandfish had no significant effects on growth and survival of shrimp. However, survival and growth of sandfish reared with shrimp for 3 weeks were significantly lower than for sandfish reared alone. Increased stocking density of shrimp also had a significant negative effect on survival and/or growth of sandfish. A grow-out trial of juvenile sandfish in 0.2-ha earthen ponds stocked with 20 shrimp post-larvae m^− 2, and densities of sandfish between 0.8 and 1.6 individuals m^− 2, confirmed that co-culture is not viable. All sandfish reared in co-culture were dead or moribund after a month. However, sandfish stocked alone into 0.2-ha earthen ponds survived well and grew to mean weights of ∼ 400 g within 12 months without addition of food. The grow-out trial demonstrated that there is potential for profitable pond farming of sandfish in monoculture. Further research is now needed to identify the optimal size of juveniles, stocking densities and pond management regimes.     

Fish polyculture system integrated with vegetable farming improves yield and economic benefits of small‐scale farmers

This study explored the yield and economic benefits of African sharptooth catfish, Clarias gariepinus, and Nile tilapia, Oreochromis niloticus polyculture, reared in earthen ponds for 270 days integrated with Chinese cabbage, Brassica rapa chinensis, farmed for 45 days to small‐scale farmers in Tanzania. An integrated aquaculture–agriculture (IAA) system involving fishes and vegetables resulted in three and 2.5 times higher net yield than the culture of fishes alone and farming of non‐integrated vegetables respectively. Vegetables irrigated with pond water resulted in 1.8 times higher net and annual yields than those irrigated with stream water. The practice of fish–vegetable integration and growing of vegetables irrigated with pond water produced 14 and 13 times higher net annual yield, respectively, than the culture of fishes alone. The integrated system produced 20 and 150 times more net returns compared with vegetables irrigated with pond and stream water respectively. Integrating fishes with vegetables resulted in significantly higher annual net cash flow than the farming of fishes and vegetables separately. The study revealed that integrating fishes with B. rapa chinensis increases yields, income and food production to small‐scale farmers. Thus, small‐scale farmers can adopt IAA technology to meet the increasing demand of fish and vegetables, stabilize their incomes and diversify food production, consequently improving food security. These benefits will be realized by providing proper training in IAA technology and management skills to small‐scale farmers.     

A Preliminary Evaluation of Naturally Occurring Organisms,Distillery By-Products,and Prepared Diets as Food for Juvenile Freshwater Prawn Macrobrachium rosenbergii

The relative acceptability and suitability of naturally occurring pond organisms identified as likely natural food items for juvenile freshwater prawn, Macrobrachiurn msenbergii, were evaluated under controlled conditions. The potential of direct consumption of materials used as organic pond fertilizer (distillers dried grains with solubles [DDGS] was also evaluated. Growth and survival of prawn fed gastropods, oligochaetes, zooplankton, or DDGS were compared with those fed a nutritionally-complete pellcted diet (control). Groups of five juvenile prawn (average weight 1.66 ± 0.10 g) were stocked into eighteen 7.5-L glass aquaria. Dietary treatments were evaluated in triplicate aquaria for 21 days. Prawn fed live zooplankton exhibited a significantly higher rate of weight gain (P < 0.05) than drawn in other treatments, as measured by differences in slopes of regression lines for weight gain over time. There were no significant differences (P > 0.05) in rates of gain for prawn fed a complete diet and those fed DDGS or gastropods. Prawn fed oligochaetes grew significantly slower (P < 0.05) than those fed the prepared diet. Results indicate that juvenile prawn as large or larger than 2g can utilize live zooplankton and that DDGS may be consumed directly by prawn. Thus, DDGS may serve a dual role as a feed and pond fertilizer. Additional research in pond management strategies that maximize zooplankton and gastropod numbers and the potential of DDGS as a combination food/fertilizer in freshwater prawn production ponds should be conducted.     

Effects of Feeding Rate on Habitat Quality in Fish Rearing Ponds

Manufactured feeds are commonly added to earthen ponds to enhance growth and survival of juvenile fish. However, excessive feeding may decrease fish production efficiency and yields by causing hypoxia (dissolved oxygen, DO < 2 mg/L) and stimulating excessive phytoplankton, filamentous green algae, and vascular plant growth. In this study, we quantified the effects of manufactured feed addition (no feeding, 1%, or 3% body‐weight/day, BW/d) on DO and inorganic phosphorus (P) and nitrogen (N) concentrations, plant abundance, and invertebrate prey production in ponds stocked with age‐0 channel catfish, Ictalurus punctatus. We found that the 3% BW/d ponds had lower DO concentrations and greater infestation by filamentous green algae (Rhizoclonium spp.) as compared to the 1% BW/d and no‐feeding ponds. Using stable N and carbon (C) isotopes to trace the fate of feed‐derived N and C in ponds, as well as analysis of zooplankton abundance, we determined that the supplied feed did not support or enhance production of natural invertebrate prey. To improve fish production efficiency, we recommend that managers leverage natural prey support of growth during early life, then adjust feeding levels to enhance growth of older fish and maintain suitable habitat quality.     

Effects of introducing ducks into fish ponds on water quality, natural productivity and fish production together with the economic evaluation of the integrated and non-integrated systems

Raising ducks on fish ponds (fish-duck culture) on a commercial scale is a new practice in Egypt, therefore, a study was undertaken to evaluate this practice from production, carcass composition and economic viewpoints.Five earthern ponds were used in the non-integrated system (no ducks) whereas four earthen ponds, in which each pond was supplied with 125 Pecking ducks per 0.42 ha, were used for the Integrated system. In both systems, each pond was stocked with four species of fish (common carp Cyprinus carpio, silver carp Hypophthalmichthys molitrix, Grey mullet Mugil cephalus and tilapias Oreochromis niloticusand O. aureus) at the same densities.There were no differences in temperature or pH in any of the ponds but dissolved oxygen levels were lower in integrated ponds concomitant with increasing levels of ammonia, phosphate and nitrate. Water in integrated ponds was richer in natural productivity (phytoplankton and zooplankton) either in species or density when compared with those variables in non-integrated ponds.Fish species reared in integrated ponds exhibited better body weight, food conversion and protein efficiency ratios compared with those of fish species in the non-integrated ponds. Fish yield per 0.42 ha produced from the integrated ponds was significantly higher than that obtained from non-integrated ones. Also, body composition of fish species was affected by the type of farming. Carcass crude protein of grey mullet, silver carp and tilapia was improved in the integrated system. The data on return on sales, return on costs, return on equity, pay-back period and break-even point showed that the integrated system was more profitable than the non-integrated system.     

Stable isotope analysis to quantify contributions of supplementary feed in Nile Tilapia Oreochromis niloticus (GIFT strain) aquaculture

Nile tilapia (Oreochromis niloticus) is currently one of the most farmed freshwater fish and contributes significantly to total global aquaculture production. The genetically improved strain of O. niloticus (GIFT) was introduced to Papua New Guinea (PNG) in 1999 to improve food and income security. The high cost and low availability of commercial fish feed hinder the growth of GIFT farming in PNG. Stable carbon and nitrogen isotopes were used to determine the role of supplementary and natural food sources in the diet of GIFT in pond‐based aquaculture. Two treatments were used: treatment 1 was daily feeding, and treatment 2 was weekly feeding, each with three replicates. Isotopic analysis of muscle tissue and all potential food sources showed that pellet feed contributed 7% to the growth of GIFT in daily‐fed ponds and 33% in the weekly‐fed ponds. Highly enriched δ¹⁵N values for chicken manure, compared to depleted values for GIFT and other natural food sources in both treatments, clearly indicate insignificant contributions of this input to production. After 90 days of cultivation, the average final body weight of GIFT receiving daily feed inputs was 134 g (average 19 cm), while for weekly‐fed it was 92 g (17 cm). The feed conversion ratio (FCR) was poor (6.4:1) in the daily‐fed GIFT ponds compared to a better, and preferable, FCR (1:1) in the weekly‐fed ponds. The findings of this study show that pelleted feed was not the major contributor to the growth of GIFT. Genetically improved farmed tilapia aquaculture should focus on enhancing natural food availability for fish production.     

Food Selection by Larval Paddlefish Polyodon spathula Supplied with Rice Bran to Promote Production of Live Foods, with Prepared Diets, or with their Combination in Earthen Ponds

Food selection of larval paddlefish Polyodon spathula was evaluated by gut analysis in nine 0.02-ha ponds either fertilized with rice bran (RB) to promote zooplankton production, supplied with prepared diets (PD), or with a combination of rice bran and prepared diet (CB). After 40 d, mean fish yields in RB and CB ponds were significantly higher ( P < 0.05) than fish yield in PD ponds, but there was no significant difference ( P > 0.05) in survival among treatments. Cladocerans were the main Live food items selected by paddlefish in RB and CB ponds. Chironomid larvae were the main food items selected by paddlefish in PD ponds. Less than 10% of the food found in paddlefish guts was prepared diets in PD and CB ponds. Prepared diets apparently were not as available to the fish or were not as preferred by the fish as Live foods. Levels of un-ionized ammonia were significantly greater in CB and PD ponds than that in RB ponds. Decomposition of uneaten high-protein diets in PD and CB ponds probably led to production of ammonia. Elevated un-ionized ammonia levels during week 5 caused abnormal swimming behavior and some paddlefish mortalities in PD and CB ponds. Based upon these results, use of RB or other organic fertilizers to promote zooplankton production is recommended over direct feeding or a combination of fertilization and feeding for larval paddlefish in earthen ponds.     

Effect of fish species combinations on water chemistry and plankton composition in earthen fish ponds

Fish-environment relationships in ponds with several different combinations of fish species are analysed. The study was carried out in 18 earthen fish ponds in a farm at Lohamei HaGetaot, Israel, during the 1986 fish culture season. Water was analysed for temperature, dissolved oxygen, pH, ammonium, nitrite, nitrate, and phyto- and zooplankton. Factor analysis was applied to the physico-chemical and plankton datasets to identify respectively the main ecological processes and species groups in the ponds. The general linear model was applied to analyse the effect of fish species combination and month on the ecological and plankton factors identified. The main source of water quality variability was accounted for by three factors: pond loading (CHF1), oxygenation of the water (CHF2), and pH effect on the second step of nitrification (CHF3). The main source of variability in the plankton composition was due to presence or absence of a blue-green algal bloom (PLF1). Another four plankton factors were identified. Each factor was differently affected by the fish species combination in the pond and the month. The complex nets of interactions between common carp, tilapia and mullet, and how these fish in different cominations affect pond water quality and food webs are discussed.     

Strategies and Tactics for Larval Culture of Commercially Important Carp

This paper reviews state-of-the-art techniques for culture of larval common carp, Cyprinus carpio, silver carp, Hypophthalmichthys molitrix, bighead carp, H. nobilis, and grass carp, Crenopharyngodon idella. Water temperature, food, and predation are important factors influencing larval survival and growth. Lower and upper lethal temperatures range from 3 to 44°C. Optimum growth temperatures range from 38 to 40°C. Lethal and optimum temperatures vary with acclimation temperature, fish age, and development stage of fish. Water temperatures are close to optimum for larval culture in tropical regions but are often too low in temperate climates. Intensive culture in temperature-controlled systems is important in temperate climates. The first food eaten by larvae in ponds consists mainly of protozoa, rotifers, and copepod nauplii. As fhe larvae grow, they quickly shift to larger food items, including cladocera and insect larvae. Management practices to enhance natural food development in earthen ponds include bottom drying, soil preparation, liming, fertilization, and agricultural crop cultivation. The development of food organisms in freshly filled ponds follows a pattern of succession. For best results, a pond should be stocked at the stage of succession when the size relationship between fish larvae (predators) and zooplankton (prey) is proper. A common practice is to stock larvae 3-7 days after filling. If ponds are filled too long before larvae are stocked, food relationships between fish and invertebrates can be reversed. Predator control includes biological, chemical, physical, and mechanical methods. Although great progress has been made in the development of dry starter diets, prepared feeds are not yet available for successful large-scale production. This problem is usually overcome by starting larvae with live food or with a mixture of live food and dry feed and by shifting larvae to dry diets as they grow. Live food either is collected from zooplankton ponds or is produced in intensive culture conditions. Systems for larval culture can range from ponds to intensive culture with water recirculation systems. Choice of the best system depends on the local climate, technical, and socio-economic conditions.     

Growth and Food Habits of Cage-Cultured Bighead Carp x Silver Carp Hybrids in Ponds of Varying Trophic Status

Four 20m³ cages stocked with 120 bighead carp x silver carp hybrids per cage were placed in each of four ponds varying in trophic status from mesotrophic to hypereutophic. Fish were cultured, without feeding, from 13 March to 1 Octorber 1987. Fish in the mesotrophic pond survived but lost weight (-0.37 g/fish/d). The mesotrophic pond produced insufficient food to sustain fish growth. Maximum fish growth rate occured in the two eutotrophic ponds (6.61vand 7/04 g/fish/d). Fish growth in the hypereutrophic pond was about one-half (3.64 g/fish/d) that in the two eutrophic ponds. Guy analysis of fish in the hypereutrophic pond revealed consumption of larger quantities (P < 0.05) of colonial blue-green algae that were apparently poorly digested and less (P < 0.05) zooplankton (primarily cladocerans) than was found in fish from the eutrophic ponds.     

Comparison of bacterial communities in channel catfish Ictalurus punctatus culture ponds of an industrial ecological purification recirculating aquaculture system

The industrial aquaculture pond system has gradually replaced the use of traditional earthen pond, as it causes less pollution and is more economical. In this study, an industrial ecological purification recirculating aquaculture system consisting of the water source pond, high‐density culture ponds, a deposit pond, and ecological purification ponds for channel catfish cultivation was established. Twelve water samples from different ponds were sequenced, and the bacterial communities were analysed. The abundances of Cyanobacteria and Merismopedia varied in different functional ponds of the system. The water quality was stable after two months of cultivation at 1.89 ± 0.22 mg/L total nitrogen, 1.1 ± 0.08 mg/L NH₄‐N and 0.43 ± 0.1 mg/L total phosphorus. The fish weight increased in a nearly linear manner, reaching 237.63 ± 23.8 per fish at day 120. An analysis of the environmental parameters, water quality and fish weight suggested that the system had an effective water purification process. Canonical correspondence analysis showed that the community was affected at the genus and phylum levels by different environmental parameters. We identified several dominant beneficial bacteria with nutrient removal abilities. Overall, our results demonstrated that the ecological purification recirculating aquaculture system had notable effects on water quality improvement and promoted changes in bacterial populations. These results provide important information on the microbial ecology of pond industrial eco‐aquaculture systems.     

The risk of parasite transfer to juvenile fishes by live copepod food with the example Triaenophorus crassus and Triaenophorus nodulosus

Natural zooplankton is a potential food resource for juvenile fish in fish farms as it is a good source of fats, carbohydrates, and protein. However, it is also a potential source of parasites and pathogens. The present study was conducted (1) to estimate the risk of parasite transfer by live copepod food under intensive farming conditions using the parasites Triaenophorus crassus and Triaenophorus nodulosus as example and (2) to look for strategies to avoid parasite infestation of juvenile fish.An easy and routinely applicable aniline blue staining method was developed to check the infestation levels of copepods with procercoids during the on-growing season of juvenile fish. From the copepod species occurring in zooplankton Cyclops spp. was infested frequently (9.4 ± 12.0%, maximum 38.7%), Diaptomus spp. infrequently (1.5 ± 1.6%, maximum 3.2%), Daphnia spp. never. Juvenile grayling, Thymallus thymallus, and corgonids, Coregonus sp., which had been fed with natural zooplankton revealed infestations rates with T. crassus of circa 5%, with T. nodulosus of circa 10%. As the occurrence of procercoids in the zooplankton was temporary limited, Triaenophorus infestation can be avoided by using artificial food instead of live copepods during the risky season.To prevent parasite infestation of juvenile fish methods were investigated to eradicate procercoids from copepods by chemical treatment (sodium chloride, hydrogen peroxide, citric acid treatment) and by freeze-thawing methods. Chemical methods failed to remove procercoids. In fish, which had been fed with frozen thawed zooplankton, no Triaenophorus spp. infestation was observed. Their survival rates were similar as in the control fed with live zooplankton, however the weight of the fish was significantly lower.     

Preliminary Comparisons of Yield and Profit Achieved from Different Rainbow Trout,Oncorhynchus mykiss,Production Systems in Inland Western Australia

Abstract

Farmers throughout the wheatbelt of Western Australia are interested in farming rainbow trout, Oncorhynchus mykiss, in saline groundwater on salt-affected farmland, to generate an alternative source of income. We compared the relative productivity and profitability of three different production systems: extensive (trout stocked in earthen ponds and totally reliant on natural food); semi-intensive (trout stocked in earthen ponds and provided with supplementary diet); intensive (trout stocked in closed, recirculating tanks). The yield of fish increased with increasing production intensity. The mean wet weight (±SE) of trout after 4 months of grow-out was 61.3±2.7 g in extensive systems, 157.9±5.2 g in semi-intensive systems and 137.9±3.9 g in intensive systems, giving mean yields of 10.8 kg/pond (13.5 kg/ha), 27.9 kg/pond (34.8 kg/ha) and 54.9 kg/tank (21.1 kg/m³), respectively. A preliminary economic analysis of the different production systems showed that the increases in yield were sufficient to balance the extra operating costs involved in semi-intensive systems, but not in intensive systems. We conclude that semi-intensive production systems deserve further study for the commercially viable production of rainbow trout from saline groundwater in Western Australia.     

Extension of nursery culture of Scylla serrata (Forsskål) juveniles in net cages and ponds

To address the preference of mud crab farmers for larger size Scylla serrata juveniles (5.0–10 g body weight or BW; 3.0–5.0 cm internal carapace width or ICW), a study was conducted to compare the growth and survival of crab juveniles (2.0–5.0 g BW; 1.0–3.0 cm ICW) produced a month after stocking of megalopae in net cages when reared further in net cages installed in earthen ponds or when stocked directly in earthen ponds. In a 3 × 2 factorial experiment, three stocking densities (1, 3 and 5 ind m⁻²), two types of rearing units (net cages or earthen pond) were used. Megalopae were grown to juvenile stage for 30 days in net cages set inside a 4000 m² brackishwater pond and fed brown mussel (Modiolus metcalfei). Crab juveniles were then transferred to either net cages (mesh size of 1.0 mm) or earthen ponds at three stocking densities. After 1 month, no interaction between stocking density and rearing unit was detected so data were pooled for each stocking density and rearing unit. There were no significant differences in the growth or survival rate of crab juveniles across stocking density treatments. Regardless of stocking density, survival in net cages was higher (77.11±6.62%) than in ponds (40.41±3.59%). Growth, however, was significantly higher for crab juveniles reared in earthen ponds. The range of mean BW of 10.5–16.0 g and an ICW of 3.78–4.33 cm obtained are within the size range preferred by mud crab operators for stocking grow‐out ponds.     

The effects of rearing water depths and feed types on the growth performance of African catfish (Clarias gariepinus)

African catfish (Clarias gariepinus) has been growing in popularity as a culture species globally. Although considerable research has been carried out on this species’ feeding preferences, no research has been carried out on optimum water level for growth. This is particularly surprising given this species' benthic nature. This study assessed the effect of different combinations of water levels and types of feed on the growth performance of African catfish. The study employed a 3 × 2 factorial design with three ponds of different water levels (0.5, 1 and 1.5 m) and two types of feeds (floating and sinking). Twelve earthen ponds (1 × 2 m) were each stocked with 16 catfish fingerlings (mean weight ~100 g), and their growth was monitored for 12 weeks. The fish cultured in the shallowest water grew significantly faster than those cultured in the deepest ponds. At the same time, fish cultured in the shallowest ponds had the lowest feed intake rates and consequently the lowest feed conversion ratios. Catfish fed sinking pellets grew faster than those fed floating pellets although the difference was not significant. There was no significant interaction between pond water depth and feed type. The results of this study suggest that the growth and feeding efficiency of C. gariepinus can be optimized by culturing in fairly shallow ponds (0.5 m).     

Split Ponds Effectively Overwinter Golden Shiners

Baitfish producers have expressed interest in adopting the split‐pond production system. However, confining fish to 20% of the pond area in split‐pond systems effectively quintuples fish density within the culture unit as compared with densities in open ponds. Winter conditions are known to be relatively more stressful on smaller fish, and high densities within split‐pond culture units could increase losses. A 139‐d study was conducted during the winter to compare the production of golden shiners, Notemigonus crysoleucas, in traditional earthen ponds and split ponds at two densities. Golden shiners were stocked at 646 kg/ha or 1292 kg/ha (ca. 370,500 or 741,000 fish/ha, respectively) into 12, 0.04‐ha, netted earthen ponds (six split ponds and six traditional). Feeding rate, nightly aeration hours, and daily circulation hours were reduced when water temperature decreased. At harvest, net yields were significantly lower in the split ponds as compared with traditional ponds at each density (53 and 113 kg/ha less in the low‐ and high‐density split‐pond treatments, respectively). Estimated survival was high (>87%) and did not differ among treatments. Results showed that, although net yield was reduced, small baitfish could be successfully overwintered in split‐pond culture units in preparation for the spring crappie market.     

Effect of supplemental feed type on water quality,plankton and benthos availability and carp (Cyprinus carpio L.) growth in semi‐intensive monoculture ponds

A four‐and‐a‐half months study was conducted in nine earthen ponds to evaluate the addition of different supplemental feeds as a management tool for enhancing natural food availability and common carp growth, while maintaining optimal water quality in the semi‐intensive system. Three supplemental feeds were used: commercial extruded and pelleted feed with 25% protein and 7% fat and cereals. The type of supplemental feed did not influence water quality, except hardness, but significantly affected abundance of cyanobacteria, natural food availability and common carp growth. The use of pelleted feed was related to the lowest abundance of cyanobacteria in the ponds. For the two groups of large zooplankton, Cladocera and Copepoda, abundances were higher in the ponds with pelleted feed compared with the ponds where cereals and extruded feed were used. The abundance of benthic macroinvertebrates in the treatment with pelleted feed was three times higher than in the other two treatments. The results of this study indicate that pelleted feed can help farmers not only as a source of nutrients for carp growth but also indirectly as a management tool for maintaining ecological stability and control of cyanobacterial bloom in ponds.