Temporary Sequestration of Fingerling Channel Catfish in Cages as a Means to Improve Production of Multiple-Crop Ponds

Abstract

Two studies were conducted to determine if temporary sequestration of fingerling channel catfish, Ictalurus punctatus, in cages improves production of multiple-crop ponds. In the first study, 0.04-ha ponds were stocked with 295 large (mean weight = 566 g) and 780 fingerling (mean weight = 21 g) catfish. Fingerlings were stocked into cages or open ponds. At 120 days after stocking, fish in cages were released. After an additional 40 days, ponds were clean-harvested to remove large (>500 g) and small (<500 g) fish. In the second study, ponds (0.08-ha) were stocked with 750 large (mean weight = 46 g) and 750 small (mean weight = 20 g) fingerling catfish. Small fingerlings were stocked into cages or open ponds. At 60 days after stocking, fish in cages were released. Market-ready fish were selectively harvested at five and nine months after stocking. Results from the first study indicated that individual weight, weight gain, and yield of both size classes of fish raised in sequestered ponds were significantly greater (P< 0.05) than that of fish raised in open ponds. In addition, total weight gain and yield of fish in sequestered ponds was significantly greater (P< 0.05) than those in non-sequestered ponds. Results from the second study indicated that a significantly greater (P< 0.05) number of market-ready fish were harvested from sequestered ponds than from non-sequestered ponds. Mean yield of sequestered ponds was 31% greater than that of non-sequestered ponds; however, differences were not significant (P> 0.05). Amount of feed fed to fish raised in sequestered ponds was significantly greater (P< 0.05) than amount of feed fed to fish raised in non-sequestered ponds in both studies. It is unclear which factor or factors were responsible for the enhanced production of sequestered ponds; however, temporary sequestration may reduce agonistic behavior and competition for feed between fish size groups.     

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.     

Production Characteristics and Economic Performance for Four Channel Catfish,Ictalurus punctatus,Pond Stocking Density-Cropping System Combinations

Fingerling channel catfish, "Ictalurus punctatus," were stocked into sixteen, 0.4-ha ponds at 11,120 fish/ha or 19.770 fish/ha. Half the ponds at either density were managed as single-batch cropping systems and half as multiple-batch cropping systems. Each of the four combinations in the 2 X 2 factorial design was replicated in four ponds over a 3-year study period. Ponds were not drained until the study was terminated. Average net fish production (totaled over 3 years) was 23,717 kg/ha for the single-batch, high-density treatment; 19,501 kg/ha for the multiple-batch, high-density treatment; 17,396 kg/ha for the single-batch, low density treatment; and 16,857 kg/ha for the multiple-batch, low- density treatment. Both stocking density and cropping system significatly (P < 0.05) influenced net production. Average size of fish at harvest was significantly (P < 0.05) lower at the high stocking density and in the single-batch cropping system. Feed conversion was better (P < 0.05) at the low stocking density and in the single-batch cropping systems. Poorer feed conversion in multiple-batch systems is believed due to harvest-to-harvest carryover of large fish, which convert feed to flesh less efficiently than small fish. Observed mortality and total fish loss (observed mortality plus fish unaccounted for upon termination of the study) were not affected (P > 0.05) by cropping system but were significantly (P < 0.05) higher in ponds stocked at the high density. Production data were used to assess discounted net revenues from a synthetic 131-ha farm based upon a price of $1.54/kg either for all fish harvested or for fish harvested that were ≥0.35kg. When based on all fish harvested, discounted net revenue was highest for the single-batch, high-density treatment, but the low average size of fish harvested from ponds in that treatment (0.49 kg/fish) would not be acceptable across the industry. The multiple-batch, low-density treatment had the second highest discounted net revenue based upon all fish harvested and the highest revenue when only fish ≥ 0.34 kg were valued. Of the treatments analyzed, this was judged the economic choice for the channel catfish industry.     

Effect of Dietary Protein Concentration and Feeding Rate on Weight Gain,Feed Efficiency,and Body Composition of Pond-Raised Channel Catfish Ictalurus punctatus1

Two experiments were conducted in earthen ponds to evaluate the effect of dietary protein concentration and feeding rate on weight gain, feed efficiency, and body composition of channel catfish. In Experiment 1, two dietary protein concentrations (28% or 32%) and four feeding rates (≤ 90. ≤ 112, ≤ 135 kg/ha per d, or satiation) were used in a factorial arrangement. Channel catfish Ictalurus punctatus fingerlings (average size: 27 g/fish) were stocked into 0.04-ha ponds at a rate of 24,700 fish/ha. Fish were fed once daily at the predetermined maximum feeding rates for 282 d (two growing seasons). In Experiment 2, three dietary protein concentrations (24, 28, or 32%) and two feeding rates (≤ 135 kg/ha per d or satiation) were used. Channel catfish (average size: 373 g/fish) were stocked into 0.04-ha ponds at a rate of 17,300 fish/ha. Fish were fed once daily for 155 d. In both experiments, five ponds were used for each dietary treatment. Results from Experiment 1 showed no differences in total feed fed, feed consumption per fish, weight gain, feed conversion ratio (FCR), or survival between fish fed diets containing 28% and 32% protein diets. As maximum feeding rate increased, total feed fed, feed consumption per fish, and weight gain increased. There were no differences in total feed fed, feed consumption per fish, or weight gain between fish fed at ≤ 135 kg/ha per d and those fed to satiation. Fish fed the 28% protein diet had a lower percentage carcass dressout and higher percentage visceral fat than fish fed the 32% protein diet. Dietary protein concentrations of 28% or 32% had no effect on fillet protein, fat, moisture, and ash. Feeding rate did not affect FCR, survival, percentage carcass dressout, or fillet composition, except fillet fat. As feeding rate increased, percentage visceral fat increased. Fish fed at ≤ 90 kg/ha per d had a lower percentage fillet fat than fish fed at higher feeding rates. In Experiment 2, dietary protein concentration or maximum feeding rate did not affect total feed fed, feed consumption per fish, weight gain, FCR, or survival of channel catfish. Feeding rate had no effect on percentage carcass dressout and visceral fat, or fillet composition. This was due to the similar feed consumption by the fish fed at the two feeding rates. Fish fed the 24% protein diet had lower carcass dressout, higher visceral fat and fillet fat than those fed the 28% or 32% protein diet. Results from the present study indicate that both 28% and 32% protein diets provide satisfactory fish production, dressed yield, and body composition characteristics for pond-raised channel catfish fed a maximum rate of 90 kg/ha per d or ahove.     

Assessment of a Phytogenic Feed Additive (Digestarom P.E.P. MGE) on Growth Performance,Processing Yield,Fillet Composition,and Survival of Channel Catfish

We investigated the effects of a phytogenic feed additive (Digestarom® P.E.P. MGE) on growth performance, processing yield, fillet composition, and survival of pond‐raised channel catfish. Fifteen 0.4 ha ponds were stocked with 14,820 catfish (126 g/fish) per ha. Fish in control ponds were fed a 32% crude protein commercial floating diet whereas fish in test ponds were fed the same diet supplemented with Digestarom P.E.P. MGE at 200 g/ton. In a second study, ten 0.04 ha ponds were stocked at a similar density with fish that averaged 68 g/fish. At the end of the 6‐mo study, there was no significant difference in the amount of feed fed or the amount of weight gained between the control and Digestarom P.E.P. MGE fed fish. Food conversion ratio, net yield, and survival were also similar between the two groups. Carcass, fillet, and nugget yield were similar. Fillet proximate analysis revealed that fillet fat was lower (P < 0.01) whereas fillet protein tended to be a little higher (P < 0.10) in treated fish. In conclusion, there was a significant reduction in the amount of fillet fat in Digestarom P.E.P. MGE fed fish. Improved fillet composition (higher protein and lower lipid) is of commercial importance.     

Effects of feeding frequency, moist and dry feeds on the growth of Chrysichthys nigrodigitatus Lacépède and on pond water quality

To examine the effects of different feeding frequencies, moist and dry feeds on the growth of Chrysichthys nigrodigitatus Lacépède and on water quality of freshwater ponds, two experiments were conducted. In one experiment, fish stocked at the same densities were subjected to three different feeding regimes using equal quantities of feed. Water quality was monitored and fish growth in the different treatments was compared. To determine the effects of moist and dry feeds, fish growth and water quality in one set of ponds fed with 5% body weight of dry feed were compared to those in another set of ponds stocked at the same rate but fed with 5% body weight of moist feed. Feeding once a day produced the greatest weight gain but fish fed once on alternate days had the best feed conversion, which was associated with pond water that had the highest dissolved oxygen. This suggests that feeding once on alternate days could be adopted as a strategy for feeding fish under unfavourable conditions. Water quality of ponds holding fish fed dry feed was better than that of ponds holding fish fed moist feed, as indicated by oxygen, carbon dioxide and ammonia contents. A highly significant difference in growth (P < 0.01) was found between fish fed moist and dry with feeds: fish performed better when fed with dry feeds.     

Effects of Periodic Feed Deprivation on Growth, Feed Efficiency, Processing Yield, and Body Composition of Channel Catfish Ictalurus punctatus

Two studies were conducted in 110‐L flow‐through aquaria and 0.4‐ha ponds to evaluate effects of periodic feed deprivation on the growth performance of channel catfish Ictalurus punctatus. Fish were deprived of feed 0, 1, 2, or 3 consecutive d/wk, l d per 5‐d period, or 3 consecutive d per 10‐d period and fed to satiation on days fish were fed. In Experiment 1, fish fed less frequently than daily consumed significantly less feed (over the experimental period) and gained significantly less weight than fish fed daily, except that feed consumption of fish deprived of feed 1 d/wk was not significantly different from that of fish fed daily. Compared with fish fed daily, fish deprived of feed 2 d/wk had significantly lower feed conversion ratio (FCR). Visceral fat of fish deprived of feed 1 or 2 d/wk was similar to that of fish fed daily, but fish deprived of feed for longer periods had significantly lower visceral fat than fish fed daily. Regression analysis indicated that feed consumption, weight gain, and visceral fat increased linearly as the number of days that fish were fed increased. In Experiment 2, there were no significant differences in the amount of feed fed between fish deprived of feed 1 d/wk and those fed daily. Net production of fish deprived of feed 1 or 2 d/wk or 1 d per 5‐d period was not significantly different from that of fish fed daily, but fish deprived of feed for longer periods had significantly lower net production than fish fed daily. Visceral fat of fish deprived of feed 1 d/wk or 1 d per 5‐d period was similar to that of fish fed daily, but fish on other treatments had significantly lower visceral fat than fish fed daily. Regression analysis showed that as the number of days fed increased the amount of feed fed and net production increased quadratically. Feed conversion ratio, carcass yield, visceral fat, and fillet fat increased, while fillet moisture decreased linearly as the number of days fed increased. Although feeding less frequently than daily may improve feed efficiency, and fish deprived of feed may demonstrate compensatory growth when a full feeding regime is resumed, it may be difficult to provide enough feed to satiate all size‐classes of fish under a multiple‐batch cropping system without causing water quality problems. Under normal economic conditions, fish should be fed daily to apparent satiation without waste and without causing water quality problems. However, during periods of unfavorable economic conditions, channel catfish raised from advanced fingerlings to market size may be fed less frequently than daily to reduce production cost. Results from the present study indicated that feeding channel catfish to satiation 5 or 6 d/wk (not feeding on one or two weekend days) could provide some benefits in reducing production cost through reduced feed and labor costs for food‐sized channel catfish during periods of low fish prices and high feed prices.     

Growth and Bone Development in Channel Catfish Fed 17-α-Methyltestosterone in Production Ponds

Effects of feeding 17-α-methyltestosterone (MT) to channel catfish ( Icralurus punctatus ) grown to harvestable size in earthen ponds were examined. Channel catfish fingerlings (mean weight, 14.4 g), stocked in 0.04 ha ponds (7,410 fish/ha) were fed diets containing MT at concentrations of 0, 2.5, and 10 mg/kg for 123 days. Weight gain by fish fed the control diet (0 MT) was higher ( P < 0.05) than that of fish fed the treated diets. Increasing the dietary concentration of MT reduced weight gain further ( P < 0.05). Both male and female fish fed MT had enlarged and thickened heads, and their skins were dark. Their dorsal and pectoral spines were short and the tips, which are normally very sharp, were soft and blunt. Weight of the rib bones per unit of length decreased ( P < 0.05) as MT was added to the diet. Breaking strength of the ribs (force required to break the bone at its midpoint) measured by an Instron shear press, was less ( P < 0.05) for fish fed MT than for control fish. The ratio of calcium to phosphorus in bones was lower ( P < 0.05) in fish fed MT. These results indicate that feeding MT at these doses (2.5 mg/kg or above) to channel catfish suppresses growth rate and reduces size and strength of bones.     

Effects of feeding frequency on the enzymes and genes involved in oxidative stress in juvenile yellow catfish Pelteobagrus fulvidraco (Richardson) exposed to ammonia

Optimal feeding strategies improve fish growth and health but may be affected by ammonia stress in closed rearing systems such as tanks or ponds. This study aimed to evaluate the effects of feeding frequency and ammonia levels in rearing water on the enzymes and genes involved in oxidative stress of yellow catfish. Experiment (ammonia exposure) and control groups were randomly assigned to one of three feeding frequencies (1, 2 and 4 times daily) for 8 weeks. Weight gain increased as feeding frequency increased from 1 to 4 times daily, but feed conversion ratio values decreased. The highest survival in ammonia group was found when fish was fed 2 times daily. Glutathione peroxidase activity and total antioxidant capacity in liver and brain of fish exposed to ammonia increased as feeding frequency increased from 1 to 4 times daily. Liver malondialdehyde content in control group decreased as feeding frequency increased from 1 to 4 times daily. The lowest liver malondialdehyde content in ammonia group was observed when fish was fed 2 times daily. Liver mRNA expression of superoxide dismutase and catalase in control group increased as feeding frequency increased from 1 to 4 times daily, but the highest superoxide dismutase and catalase expression in ammonia group were observed when fish were fed 2 times daily. This study indicates that higher feeding frequency of yellow catfish exposed to ammonia could result in oxidative stress and poor survival. The optimal feeding frequency of yellow catfish exposed to ammonia is 2 times daily.     

Effect of Dietary Protein Concentration and Stocking Density on Production Characteristics of Pond-Raised Channel Catfish Ictalurus punctatus

Diets containing 28% and 32% crude protein were compared for pond‐raised channel catfish Ictalurus punctatus stocked at densities of 14,820, 29,640, or 44,460 fish/ha. Fingerling channel catfish with average initial weight of 48.5 g/fish were stocked into 30 0.04‐ha ponds. Five ponds were randomly allotted for each dietary protein ± stocking density combination. Fish were fed once daily to satiation for two growing seasons. There were no interactions between dietary protein concentration and stocking density for any variables. Dietary protein concentrations (28% or 32%) did not affect net production, feed consumption and weight gain per fish, feed conversion ratio, survival, processing yields, fillet moisture, protein and ash concentrations, or pond water ammonia and nitrite concentrations. Fish fed the 32% protein diet had slightly but significantly lower levels of visceral and fillet fat than fish fed the 28% protein diet. As stocking density increased, net production increased, while weight gain of individual fish, feed efficiency, and survival decreased. Stocking densities did not affect processing yield and fillet composition of the fish. Although highly variable among different ponds and weekly measurements, ponds stocked at the highest density exhibited higher average levels of total ammonia‐nitrogen (TAN) and nitrite‐nitrogen (NO₂‐N) than ponds stocked at lower densities. However, stocking density had no significant effect on un‐ionized ammonia‐nitrogen (NH₃‐N) concentrations, calculated based on water temperature, pH, and TAN. By comparing to the reported critical concentration, a threshold below which is considered not harmful to the fish, these potentially toxic nitrogenous compounds in the pond water were generally in the range acceptable for channel catfish. It appears that a 28% protein diet can provide equivalent net production, feed efficiency, and processing yields as a 32% protein diet for channel catfish raised in ponds from advanced fingerlings to marketable size at densities varying from 14,820 to 44,460 fish/ha under single‐batch cropping systems. Optimum dietary protein concentration for pond‐raised channel catfish does not appear to be affected by stocking density.     

Effects of Feeding Diets Containing 34 or 38% Protein at Two Feeding Frequencies on Growth and Body Composition of Channel Catfish

Channel catfish, Ictalurus punctatus, fingerlings were stocked (13,585 fish/ha) in twelve 0.04-ha earthen ponds and fed to satiation with diets containing either 34 or 38% protein (79.1 or 88.8 mg protein/kcal), either once or twice daily for 170 days. Experimental diets with the proper levels of essential amino acids, vitamins, and minerals were formulated by a commercial feed mill. No significant differences (P < 0.05) in growth and body composition of channel catfish were found when analyzed by protein level, feeding frequency, or their interaction. Average individual fish weight at harvest was 461 g. Net production was 4,152 kg/ha. Percentage protein, fat, and ash in the waste (head, skin, viscera, and frame) were 41.5, 41.4, and 12.2%, respectively, while fillet had 65.7, 30.4, and 4.0%, respectively.     

POLYCULTURE OF CHANNEL CATFISH (Ictalurus punctatus) WITH ALL-MALE TILAPIA HYBRID

Channel catfish (Ictalurus punctatus) (x? = 0.8 g) and all-male hybrid tilapia fingerlings (Sarotherodon mossambica ♂ × S. hornorum ♀) (x? = 35.0 g) were stocked in 0.04 ha replicated ponds in Baton Rouge, Louisiana, in March and July 1981, respectively. The ponds were stocked at densities of 11,110 catfish per ha, 11,110 catfish with 5,550 tilapia per ha, 7,400 catfish per ha, and 7,400 catfish with 3,700 tilapia per ha. The fish were fed daily at 4% of estimated catfish biomass and were harvested in November 1981. There were no differences in dissolved oxygen or water temperature among the four culture systems (P > 0.05). The presence of tilapia, however, significantly increased water turbidity, pH and chlorophyll a concentrations (P < 0.05). Tilapia did not improve water quality and may have deteriorated it. Tilapia did not affect channel catfish growth or production (P > 0.05), but the presence of tilapia did significantly increase total fish yield (P < 0.05) by 13.5 and 32.2% at low and high catfish densities, respectively. Channel catfish and tilapia averaged 390 and 245 g at harvest, respectively. Overall catfish survival averaged 61%. Tilapia survival was 72% and 61% at low and high densities, respectively.     

Effect of Stocking Density on Growth and Water Quality for Largemouth Bass Micropterus salmoides Growout in Ponds

Juvenile largemouth bass Micropterus salmoides , trained to accept artificial diets, were stocked into six 0.04-ha ponds at stocking densities of either 6,175 or 12,350 fish/ha. Fish were fed a floating custom-formulated diet, containing 44% protein, once daily to satiation for 12 mo (May 1994–May 1995). At final harvest, the total yield of fish was significantly greater (P < 0.05) and feed conversion ratio (FCR) was significantly lower, for bass stocked at the higher density (4,598 kg/ha and 2.3, respectively) than when stocked at the lower density (2,354 kg/ha and 3.3, respectively). There was no significant difference (P > 0.05) in average weight, length, or survival of bass stocked at the two densities. Averaged over the study period, there were no significant differences (P > 0.05) in total ammonia-nitrogen (TAN), nitrite-nitrogen, or un-ionized ammonia concentrations in ponds in which bass were stocked at the two densities. These data indicate that largemouth bass of the size used in this study are amenable to pond culture at densities of at least 12,350 fish/ha and that higher stocking densities may be possible.     

Production Characteristics of Pond-Raised Channel Catfish Ictalurus punctutus Fed Diets With and Without Animal Protein for Three Growing Seasons1

An experiment was conducted to determlne the long-term effects of an all-plant-protein diet on production characteristics (harvest yield, dressing percentage, and body composition) of catfish Ictalurus punctatus taken from top-harvested, multiple-stocked ponds over a 2.5-yr period of continuous production. Fish in eight 0.08-ha ponds were fed an extruded, 32% protein control diet (CON) containing animal and plant proteins, while fish in eight replicate ponds were fed an isonitrogenous diet containing only plant proteins, primarily from cottonseed meal and soybean meal (APP). Diets were fed once dally to apparent satiation during the growing season. Ponds were top-harvested twice per year in the spring and fall and partially restocked after each harvest. CON-fed fish received 13,335 kg of feed during the 2.5-yr period. APP-fed fish received 13,506 kg of feed. Total yields were 5,562 kg of CON-fed fish and 5,840 kg of APP-fed fish; average annual yields were 3,477 kgha per yr and 3,650 kgha per yr, respectively (P > 0.05). Feed conversion ratios, 2.5 for CON-fed fish and 2.6 for APP-fed Ash, did not differ significantly (P > 0.05). Live weights at harvest averaged 529 g (CON) and 481 g (APP), and were not significantly different. Dressing percentages were 59% for fish fed both diets (P > 0.05). APP-fed fish had less (P < 0.05) visceral fat and less (P < 0.05) muscle lipid than CON-fed fish. Results indicate that a lysine supplemented, all-plant-protein diet containing 40% cottonseed meal and 20% soybean meal is suitable for long-term production of channel catfish in earthen ponds and such a diet can reduce the fat content of pond-reared fish.     

不同饲料料型及投喂频率对斑点叉尾鮰幼鱼生长及肌肉品质的影响

本研究旨在探究不同饲料料型及投喂频率对斑点叉尾鮰(Ictalurus punctatus)生长及肌肉品质的影响。研究采用双因素试验设计,以饲料料型(膨化饲料,EF;颗粒饲料,PF)和投喂频率(2次/日,F2;3次/日,F3)为影响因素,共4个组,分别命名为EFF2、PFF2、EFF3和PFF3,每组3个平行,投喂8周,每天定时投喂两次(7:30和16:30)或3次(7:30, 12:00, 16:30)。结果显示,斑点叉尾鮰的末重和增重率受到投喂频率的影响,F2组显著高于F3组(P0.05);而饲料料型则对斑点叉尾鮰的生长无显著影响(P0.05)。颗粒饲料组的肌肉粗脂肪含量和内聚性、回复性显著低于膨化饲料组(P0.05),而硬度显著高于膨化饲料组(P0.05)。F3组的肌肉硬度、胶着性和咀嚼性则显著高于F2组(P0.05)。颗粒饲料组生肌调节因子5 (myogenic factor 5, Myf5)和肌肉生长抑制素(myostatin,MSTN)基因的相对表达量显著低于膨化饲料组(P0.05)。F3组肌肉中MSTN基因相对表达量显著高于F2组,而肌细胞生成素(myogenin,MyoG)基因相对表达量则呈现相反趋势。综上,投喂同种配方的膨化饲料和颗粒饲料对斑点叉尾鮰的生长效果相似,但是投喂颗粒饲料的斑点叉尾鮰硬度更大,而投喂膨化饲料则肌肉脂肪含量更高;斑点叉尾鮰的最佳投喂频率是每天2次。     

Effects of Protein Level and Feeding Frequency on Growth and on Body Composition of Third-Year Channel Catfish Cultured in Ponds

Channel catfish, Ictalurus punctatus, adults were stocked at 3,705 fish/ha in twelve 0.04-ha earthen ponds and fed to satiation either once or twice daily with diets containing either 32 or 38% protein for 170 days. Experimental diets with the appropriate levels of essential amino acids, vitamins, and minerals were formulated by a commercial feed mill. There were no significant differences (P > 0.05) in growth and body composition of channel catfish when analyzed by protein level, feeding frequency, or their interaction. Average individual fish weight at harvest was 1,600 g. Average net production was 3,125 kg/ha. Dry-weight percentages of protein, fat, and ash in the carcass were 55.5, 38.1, and 6.7%, respectively, and in the waste (head, skin, and viscera) were 40.5, 43.2. and 12.5%. respectively. Third-year channel catfish may be able to utilize a diet with lower (<32%) protein levels and a reduced energy: protein ratio.     

Evaluation of potassium ricinoleate as a selective blue-green algicide in channel catfish ponds

The effectiveness of potassium ricinoleate as a selective blue-green algicide was investigated in experimental channel catfish, Ictalurus punctatus, culture ponds. Five ponds were treated with 0.8 mg/l potassium ricinoleate three times per week from May through October and five ponds served as controls. Treatment did not affect concentrations of chlorophyll-a, total and un-ionized ammonia-nitrogen, or dissolved oxygen; nor did it affect average hours of supplemental aeration or net fish production. The mean nitrite-nitrogen concentration in control ponds was higher (P<0.05) than that in treated ponds, but concentrations of nitrite never reached levels considered detrimental to the health of the fish. Treatment did not reduce the incidence or percentage of blue-green algae in phytoplankton communities and did not prevent severe episodes of off-flavor in fish from treated ponds.     

Effect of Time of Feeding on Growth of Channel Catfish1

Channel catfish fingerlings were stocked into 16 0.04-ha ponds at a rate of 24,700 fish/ha on 5 May 1992. Four replicate ponds were used for each of the following treatments: 1) fed once daily at 0830h; 2) fed once daily at 1600h; 3) fed once daily at 2000h; and 4) fed on demand using demand feeders. Fish on the first three treatments were fed to satiation. All fish were harvested 145d after stocking. Results from this study showed that when channel catfish raised in ponds were fed once daily to satiation, time of feeding had no significant impact on water quality, feed consumption, feed conversion, weight gain, or body proximate composition. Fish fed on demand consumed more feed than fish fed once daily to satiation, but difference in weight gain was not significant. These data indicated that feeding time may not be critical for channel catfish production as long as fish are fed when dissolved oxygen is sufficient. Although feeding at night was not detrimental in this study, night feeding is not recommended on large ponds unless sufficient aeration is available to quickly provide oxygen in an emergency—and even then it would be problematic.     

Effect of dietary Yucca schidigera extract on growth,total ammonia–nitrogen excretion and haematological parameters of juvenile striped catfish Pangasianodon hypophthalmus

A feeding trial with striped catfish, Pangasianodon hypophthalmus was performed to determine the effect of Yucca schidigera in practical diet on the growth, feed utilization, body composition, total ammonia–nitrogen (TAN) excretion and haematological parameters. A diet with fish meal as the main protein source without yucca extract was used as the control diet (Diet 1). Four diets were formulated with 0.075 (Diet 2), 0.1 (Diet 3) and 0.15 (Diet 4)% of yucca extract respectively. Fifteen fish per tank (initial mean weight 1.78 ± 0.05 g) were randomly allocated to 15 fibreglass tanks (80‐L) connected to a freshwater closed recirculation system (temperature 29.7 ± 1.0°C). The experimental diets were tested in triplicates for 12 weeks. The specific growth rate of fish fed Diet 4 was significantly higher when compared with fish fed Diet 1. The growth of fish fed diets Diet 2 and Diet 3 were not significantly different compared with fish fed the Diet 1. Striped catfish fed Diet 4 had significantly lower feed conversion ratio compared with fish fed Diet 1 and Diet 2 (P < 0.05).The incorporation of high level Yucca schidigera extract in the diets reduced TAN compared with Diet 1. Dietary inclusion of Yucca extract levels did not significantly affect the biometric parameters or whole body proximate composition of the striped catfish (P > 0.05). The PCV (%) in fish significantly increased with high levels of Yucca inclusion (Diet 4) compared with control diet. Fish fed Diet 4 showed significantly higher haemoglobin levels than Diet 1 (P < 0.05). The results indicate that dietary inclusion of Yucca schidigera extract is promising as a feed additive that could improve growth performance and some haematological parameters and the best Yucca schidigera level was 0.15%.     

Effects of dietary Nutrafito Plus on growth,haemotological parameters and total ammonia‐nitrogen excretion of juvenile striped catfish Pangasianodon hypophthalmus

A feeding trial was performed to determine the effect of a commercial source of Yucca schidigera and Quillaja saponaria extracts (Nutrafito Plus^®), in practical diets, on striped catfish Pangasianodon hypophthalmus growth, feed utilization, body composition, total ammonia‐nitrogen (TAN) excretion and haematological parameters. Four experimental diets were supplemented with Nutrafito Plus^® at 0%, 0.01%, 0.02% and 0.03% (diets: control, N01, N02 and N03 respectively). Three replicate groups of striped catfish, with initial mean weight of 1.78 ± 0.05 g, were fed one of the four diets for 12 weeks. The specific growth rate (SGR) and final weight of fish fed diet N03 was significantly higher (P < 0.05) than fish fed the other dietary treatments. The growth performance of fish fed diets N01 and N02 were not significantly different compared to fish fed the control diet. Striped catfish fed diet N03 had improved feed conversion ratio (FCR), net protein utilization (NPU) and protein efficiency ratio (PER) than the control (P < 0.05). The inclusion of the high dietary level of Yucca schidigera and Quillaja saponaria, diet N03, reduced TAN compared to all groups. Dietary inclusion of Yucca schidigera and Quillaja saponaria at all levels investigated did not affect the whole body proximate composition of the striped catfish (P > 0.05). The packed cell volume (PCV) and haemoglobin level in fish fed diet N03 was significantly higher than in the fish fed the control diet. The present study demonstrates that dietary inclusion of Yucca schidigera and Quillaja saponaria induced positive effects on growth performance and haematological parameters and decreased TAN excretion in striped catfish.