Use of Cottonseed Meal in Channel Catfish Feeds

Solvent extracted cottonseed meal was substituted for soybean meal in catfish feeds on a nitrogen basis. The feeds, which contained either 0, 10, or 20% cottonseed meal, were formulated to contain about 32% protein and 2.9 kcal digestible energy/g. The fish were reared in 6 m³ net pens suspended in a 1.6 ha earthen pond. Twelve pens (four per treatment) were stocked with 400 fish with an initial average weight of 95 g/fish. All fish were fed to satiation once daily. A sample of 60 fish from each pen was weighed at 76 days to evaluate feed consumption, feed conversion, and weight gain. At the end of the experiment (132 days), fish from each net pen were weighed collectively and samples were taken to determine tissue free gossypol concentrations, proximate composition of fillets, and dressout percentages. There were no significant differences in weight gain, feed conversion, or survival of fish sampled at 76 days or of fish at the end of the experiment regardless of dietary treatment. At 76 days, feed consumption of fish fed the 20% cottonseed meal feed was significantly higher than that of other fish, but there were no significant differences in feed consumption at the end of the experiment. Free gossypol levels were below detectable limits in fish tissue. There were no significant differences in percentage dressout or in body composition, except for a slightly higher ash content in fish fed the feed containing 10% cottonseed meal. It appears that cottonseed meal can be used to partially substitute for soybean meal in catfish feeds. At the present, it is recommended that cottonseed meal be limited to 15% of the catfish diet.     

Nitrogen recovery in a decoupled aquaponic system with lamellar settler and trickling biofilter: implications for system management

Careful nitrogen (N) management will be needed to nourish the growing human population while minimizing adverse environmental impacts. Aquaponic systems (AS) have a great potential to become a sustainable technology making further use of N-rich aquaculture wastewater. In the present study, we observed the N retention and losses in a running prototype of decoupled AS with Nile tilapia (Oreochromis niloticus) and tomatoes (Solanum lycopersicum) over 24 days. N losses amounted to 32.5% of feed N input and were observed in the recirculating aquaculture system (RAS) of the AS. Fish retained 21.1% of N input while 25.2% of N input accumulated in the RAS water. About 14.1% of the loss of N was caused probably by anaerobic denitrification processes in the lamellar settler (LS). In addition, 18.4% of N input was discharged during the three cleanings of LS. In the hydroponic unit of the AS that has been due to space limitations much smaller than an optimized AS could be (only about 20% of the optimal size relative to fish biomass), the tomato plants, including fruits, leaves, and stems, recovered 3.1% of N input with water uptake of 1700 L. The fish culture management, system design, and environmental management in the greenhouse affect the N recovery in the decoupled AS.

     

Nutrient dynamics in integrated aquaculture–hydroponics systems

Changes in concentrations of dissolved Ca, Cu, Fe, K, Mg, Mn, NO₃-N, Na, P, and Zn, as a function of increasing biomass of Nile tilapia (Oreochromis niloticus) fed a commercial diet in integrated aquaculture–hydroponic systems growing romaine lettuce (Lactuca sativa longifolia cv. Jericho), were monitored over three, 28-day experimental trials. The integrated systems, 320–330 l in volume, were filled initially with a complete nutrient hydroponic solution, and were operated at a 100% recirculation rate. Treatment levels were 0 (control) 151, 377, 902, and 1804 g of fish/system and treatments were conducted in duplicate. Nutrient concentrations and mutual ratios of nutrients quickly departed from initial conditions because the relative proportion of dissolved nutrients excreted by fish and subsequently absorbed by plants differed. The removal of nutrients by lettuce, fish, and solids collection was determined as a function of treatment size. The objective of this study was to quantify both the flow of nutrients through representative integrated aquaculture–hydroponics systems and the effects of different quantities of feed nutrient input on changes in nutrient-specific concentrations.     

杂交鳢和乌鳢池塘养殖对比试验

对杂交鳢和乌鳢进行池塘养殖对比试验.前者投喂人工饲料,后者投喂冰鲜鱼,结合水质调控和病害防治等技术,杂交鳢成活率80.9%,乌鳢53.9%;杂交鳢平均单产为5.2 kg/m~2,饵料系数1.367;乌鳢1.8 kg/m~2,饵料系数4.29.整个养殖过程杂交鳢塘换水2次,乌鳢塘换水6次.     

Analysis of nutrient flows in integrated intensive aquaculture systems

This paper analyses nutrient conversions, which are taking place in integrated intensive aquaculture systems. In these systems fish is cultured next to other organisms, which are converting otherwise discharged nutrients into valuable products. These conversions are analyzed based on nitrogen and phosphorous balances using a mass balance approach. The analytical concept of this review comprises a hypothetical system design with five modules: (1) the conversion of feed nutrients into fish biomass, the “Fish-Biomass-Converter”; (2) the separation of solid and dissolved fish waste/nutrients; the “Fish-Waste-Processor”; (3) the conversion of dissolved fish waste/nutrients, the “Phototrophic-herbivore-Converter”; (4 and 5) the conversion of solid fish waste, the “Bacterial-Waste-Converter”, or the “Detrivorous-Converter”. In the reviewed examples, fish culture alone retains 20–50% feed nitrogen (N) and 15–65% feed phosphorous (P). The combination of fish culture with phototrophic conversion increases nutrient retention of feed N by 15–50% and feed P by up to 53%. If in addition herbivore consumption is included, nutrient retention decreases by 60–85% feed N and 50–90% feed P. This is according to the general observation of nutrient losses from one trophic level to the next. The conversion of nutrients into bacteria and detrivorous worm biomass contributes only in smaller margins (e.g. 7% feed N and 6% feed P and 0.06% feed N 0.03 × 10⁻³% feed P, respectively). All integrated modules have their specific limitations, which are related to uptake kinetics, nutrient preference, unwanted conversion processes and abiotic factors.     

Chemical Budgets for Organically Fertilized Fish Ponds in the Dry Tropics

Chemical budgets were determined for nitrogen, phosphorns, dissolved oxygen and chemical oxygen demand for three 0.1-ha earthen ponds stocked with Onwchrornis nilotieus at the El Carao National Fish Culture Research Center, Comayagna, Honduras, for two 150-d culture periods, corresponding to the rainy and dry seasons. Layer chicken litter was added to ponds weekly at 500 kg dry matter/ha. Concentrations of nitrogen (N), phosphorus (P), and chemical oxygen demand (COD) in pond water increased during each season. No significant seasonal differencea in concentrations of water quality variables were observed. Chicken litter added to ponds represented 92–94% of N input, 93–95% of P input, and 43–52% of COD input. Photosynthesis by phytoplnnkton provided 47–56% of COD and 98% of dissolved oxygen (DO) added to ponds. Net inward diffnsion of oxygen added 1.2–1.5% of total DO. Regulated inflow was a minor source of nutrients, and contributed 3–4% of input N, 3–4% of input P, 1% of COD input, and 1% of DO input. Nutrient inputs from rain were ≤1% of total for each nutrient. Fish harvest accounted for 18–21% of total N, 16–18% of total P and 2% of COD added to ponds. Community respiration accounted for 48–57% of COD and 99.5% of DO added to ponds. Nutrient losses in pond effluent at draining were: 7–9% of total N, 29–37% of total P and 2–3% of COD. While measured gains exceeded measrued losses, significpntly greater N, P and organic matter concentrations in pre-drain samples indicated pond mud was a major sink for added nutrients, accumulation in mud represented 70% of total N, 35–40% of total P, and 38–46% of COD.     

Timing of Supplemental Feeding for Tilapia Production

The staged addition of feed to fertilized fish ponds was evaluated by adding fertilizers to 15 ponds stocked with Nile tilapia Oreochromis niloticus , then adding feed at half ad libitum rates once fish in the ponds reached a target weight. Each pond was stocked with 750 fish (3 fish/m²), and each treatment included three ponds with first feeding at (a) 50 g, (b) 100 g, (c) 150 g, (d) 200 g, and (e) 250 g. Ponds in Thailand (at the Ayutthaya Freshwater Fisheries Station, Royal Thai Department of Fisheries) were maintained for 236–328 d until the fish reached 500 g.
Growth was similar for all treatments under fertilizer alone (1.17 g/d) and was also similar when feed was applied (3.1 g/d). Feed application rates averaged 1.17% BW/d, indicating substantial use of natural food. Pond water quality did not deteriorate under supplemental feeding. Feed conversion rates averaged 1.03. Multiple regression indicated that 73.8% of the variance in growth was explained by design variables (feed input and days), while 86.2% of the variance in growth was explained by adding dissolved oxygen content and alkalinity into the equation.
The most efficient system was to grow fish to 100–150 g with fertilizers alone, then add feed. First adding feed (at 50% ad libitum) once fish reached 100 g produced the highest predicted annual revenues ($6,164 per hectare). Results of this experiment indicated that either critical standing crop occurred early (before the first fish sample) or did not occur at all in these ponds.     

Supplemental Feeding of Tilapia in Fertilized Ponds

The addition of feed to fertilized fish ponds was evaluated by adding feed alone, feed plus fertilizer, or fertilizer alone to nine ponds stocked with Nile tilapia Oreochromis niloticus . Two experiments were conducted. The first had 500 fish per 250 m² pond in 3 treatments: ad-libitum feeding; fertilizer only; or fertilizer and ad-libitum feeding. The second experiment had 5 treatments with 750 fish per pond ad-libitum feed only; fertilizer only; or 0.25, 0.50, and 0.75 satiation ration plus fertilizer. Ponds in Thailand were maintained for 155–162 d, during which chemical and physical properties were monitored. In experiment 1 tilapia growth was highest in feed only ponds, and lowest in fertilizer only ponds. Net yield did not differ significantly among treatments, due to variation in survival. In experiment 2, tilapia growth was lowest in fertilizer only ponds, intermediate in 0.25 ration ponds, and highest in 0.50, 0.75, and ad-libitum ponds. The latter treatments were not significantly different. Multiple regressions for each experiment indicated only 47–87% of the variance in growth was explained by feed and fertilizer input, while 52–89% of the variance in yield was explained by those factors. For both experiments combined, 90.3% of the variance in growth was explained by feed input, fertilizer input, alkalinity, and total inorganic nitrogen concentration. For yield, R ² was 0.888 and the regression included feed input, pH, and number of low dissolved oxygen events. Experiment 1 appeared to approach carrying capacity near the end, while no reduction in growth occurred in experiment 2 at higher fish density and biomass. Reductions in growth in experiment 1 were not correlated with declining water quality late in the grow out. Combinations of feed and fertilizer were most efficient in growing tilapia to large size (500 g) compared to complete feeding or fertilizing alone.     

深水网箱高体(鱼师)养殖试验报告

通过对均重1 225 g的大规格高体(鱼师)苗种进行252天的深水网箱养殖,高体(鱼师)的平均体重由1 225 g增至3 350 g, 共收成鱼5 521尾,养殖成活率92.02%,杂鱼饵料系数7.76。     

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 common carp Cyprinus carpio (L.) and feed addition in rohu Labeo rohita (Hamilton) ponds on nutrient partitioning among fish, plankton and benthos

The effects of introducing common carp (CC) and of adding artificial feed to fertilized rohu ponds on water quality and nutrient accumulation efficiency were studied. All ponds were stocked with 15 000 rohu ha^?1. Treatments included ponds with rohu alone, rohu plus 5000 common carp ha^?1 and rohu plus 10 000 CC ha^?1. A comparison was also made between supplementally fed and non‐fed ponds. The overall highest nitrogen (N) and phosphorus (P) concentrations were observed in ponds with 5000 CC ha^?1, followed by ponds with 10 000 and 0 CC ha^?1. The largest fractions of N and P inputs accumulating in fish, phytoplankton and zooplankton were observed in ponds with 5000 CC ha^?1, followed by ponds with 10 000 CC ha^?1 and subsequently ponds without CC. Relatively more nutrients accumulated in benthic organisms in ponds without than in ponds with CC. A smaller fraction of the nutrient input was retained in fish, plankton and benthic organisms in ponds without CC compared with ponds with CC. Compared with 5000 CC ha^?1, stocking 10 000 CC ha^?1 can be considered as overstocking, because this leads to lower fish production and relatively less nutrients retained in plankton and benthic organisms.     

Effects of supplementary feeds with different protein levels on growth and economic performances of Nile tilapia (Oreochromis niloticus) cultured in a rain-fed rice–fish ecosystem

This study investigated the effects of supplementary feeds with different crude protein (CP) levels on the growth and economic performances of sex-reversed Nile tilapia (Oreochromis niloticus) reared in a rain-fed rice–fish ecosystem for a period of 120 days. There were four treatments—namely, traditional feed (21% CP), formulated feed (26% CP), commercial feed (30% CP), and control (no feed was used)—with three replicates per treatment. Fish (30.04 g) were stocked in ditches at a rate of 0.5 fish m^?2 considering the total area and fed one of the tested feeds twice daily at the rate of 2%–5% of body weight. Water-quality parameters of the ditches were monitored fortnightly, and these parameters were found suitable for fish farming. Organic matter, total nitrogen, and available phosphorous in soil were increased significantly (P < 0.05) in the feed treatments after fish cultivation. Highly significant weight gain and SGR were observed with fish fed the commercial feed as compared with other treatments. The highest benefit-cost ratio (2.15) was found in the control, followed by formulated feed (1.90), but in the case of numerical net return, it was the opposite. However, commercial feed showed the lowest benefit-cost ratio (1.67) due to higher feed cost than other supplementary feeds. Therefore, this study suggests that fish fed with a formulated feed (26% CP) produced significantly higher net economic return in the rice–fish farming system.     

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.     

Appropriate Timing of Supplemental Feeding for Production of Nile Tilapia, Silver Carp, and Common Carp in Fertilized Polyculture Ponds

In an attempt to identify appropriate times for initial application of supplemental feed in polyculture fertilized fish production earthen ponds, a study was conducted for 19 wk to establish the growth performance, yield, survival, and body composition of Nile tilapia, common carp, and silver carp as influenced by four different feeding regimens (treatments). The four treatments were: 1) supplemental feeding beginning at onset of the experiment (T-I) (control treatment); 2) 6-wk delay of feeding after fish stocking (T-II); 3) 13-wk delay of feeding after fish stocking (T-III), and 4) no supplemental feed application (T-IV). Two ponds were assigned to each treatment and each pond was stocked with a similar number and weight of each fish species. A commercial pelleted fish feed (25% protein) was used to feed fish in T-I, T-II, and T-III at 3% of their body weight, twice a day. At the end of the experiment, fish species (except for silver carp) in T-II showed weight gain, growth rates, and yields significantly higher than fish in T-III or T-IV. Also, the total fish production and net profit in T-II were significantly higher than in T-III or T-IV. Fish species in T-II showed weight gain, growth rates, survival rates, and yields similar to those of T-I (control treatment) with no significant differences. The amount of feed consumed by fish in T-II was reduced by approximately 7.3% compared to that consumed by fish at T-I. Moreover, there was increase in th net profit in T-II by 4.8% over that achieved in T-I. Therefore, T-II appears to be the most appropriate among the tested feeding treatments and recommended for use in order to achieve the best growth, production, and net profit.     

Effect of replacing fish meal with soybean meal on growth,feed utilization and nitrogen and phosphorus excretion of juvenile Pseudobagrus ussuriensis

An 8‐week feeding trial was conducted to evaluate the effects of replacing fish meal with soybean meal (SBM) on growth, feed utilization, and nitrogen (N) and phosphorus (P) excretion of juvenile Pseudobagrus ussuriensis (initial average weight 0.50 ± 0.00 g). Seven isonitrogenous and isolipidic diets were formulated to contain SBM to replace fish meal protein at 0% (S0), 10% (S10), 20% (S20), 30% (S30), 40% (S40), 50% (S50) and 60% (S60) respectively. To investigate the effects of supplementation with crystalline amino acid to balance diet S60, one diet was formulated to add 0.30% methionine (SM60). The results showed that there was no significant difference in weight gain among fish fed S0, S10, S20, S30 and S40 diets, however, a significant reduction in this variable occurred when 50% and 60% of fish meal protein was replaced by SBM (P < 0.05). Apparent digestibility coefficients of dry matter, crude protein and phosphorus of diets were affected by dietary SBM levels. N and P excretion indicate that fish meal replacement by SBM led to an increase in N excretion, but led to a reduction in P excretion. No differences were detected in growth, feed utilization and N and P excretion between fish feed diets S60 and SM60. The results of this study show that 40% of fish meal protein could be replaced by SBM in diets of juvenile P. ussuriensis without having a significant negative effect on growth or feed efficiency, but that higher dietary SBM levels reduce fish performance.     

Feed efficiency, nutrient retention and body composition of Nile tilapia, Oreochromis niloticus L., fed diets containing L-ascorbic acid, L-ascorbyl-2-sulphate or L-ascorbyl-2-polyphosphate

Seven purified diets were formulated and fed to seven groups of Nile tilapia, Oreochromis niloticus L., fingerlings for 12 weeks. Six of the formulated diets contained 5 or 50 mg kg^?1 of ascorbic acid equivalent supplied by either L-ascorbic acid (AA), L-ascorbyl-2-sulphate (AS) or L-ascorbyl-2-polyphosphate (APP). The seventh basal diet was ascorbate-free and served as the control. The results of diet analysis for ascorbic acid showed that it was not detected or negligible in the control diet and in the diets containing AA at the end of the experiment, whereas there was no loss of ascorbic acid from diets prepared with AS or APP. The results demonstrated that the feed efficiency and growth parameters in fish fed APP-5, AS-5, AA-5 or AA-50 diets were statistically similar to the same parameters in fish fed the control diet. The study indicated that diets supplemented with 5 or 50 mg kg^?1 ascorbic acid in the form of APP or AS were more effectively utilized as sources of vitamin C than equimolar AA in promoting growth, improving food efficiency, increasing nutrient retention and preventing scurvy in Nile tilapia. Fish fed the ascorbate-free diet and the diet containing 5 mg AA kg^?1 exhibited external signs of scurvy during the last growth period of the experiment. Diets containing 5 mg kg^?1 of ascorbic acid from AS or APP provided some growth with no overt signs of scurvy, indicating that this concentration of AS and APP might be near the minimum requirement for the species. The APP-50 diet was the most efficient, and significantly (P < 0.05), had the lowest value of the amount of dietary protein necessary for 100 g weight gain (dietary protein index, DPI), the highest values of feed conversion efficiency (FCE) and the highest values of nutrient retention, i.e. protein (PRV), fat (FRV), ash (ARV) and gross energy (ERV) compared to the other diets. Fish that received the APP-50 diet had a significantly (P < 0.05) higher weight and protein gains in tissues than the other fish groups. The increase in the feed efficiency and growth parameter values in fish receiving the APP-50 diet compared with the values for the same parameters in the AA-50 diet were calculated as percentages, and the results were: weight gain, 36.2%; protein gain, 40.9%; FCE, 53.3%; PRV, 58.1%; FRV, 34.9%; ARV, 57.4%; and ERV, 51.9%. The diet containing APP-50 was followed in order by the AS-50 diet. The AS-50 diet had statistically comparable (P > 0.05) values of weight gain, protein gain and FRV to the APP-50 diet. The increased feed efficiency and growth parameters values of fish receiving the AS-50 diet compared with the AA-50 diet were calculated as percentages, and the results were: weight gain, 2 7.9%; protein gain, 27.9%; FCE, 18.2%; PRV, 17.9%; FRV, 19.2%; ARV, 8.9%; and ERV, 18.2%. There were no significant (P > 0.05) differences between the groups in the percentages of moisture, protein and ash in whole fish at the end of the study, whereas lipid percentages were significantly (P < 0.05) lower in all the tested groups in comparison with the control fish. Increasing the level of ascorbic acid equivalent from 5 to 50 mg kg^?1 diet from APP, AS or AA reduced the percentage of fat in Nile tilapia bodies. These results indicate that all the tested vitamin C sources were effective in inducing lipolysis in Nile tilapia tissues.     

投喂不同饵料对长薄鳅生长的影响

在水温18.6～21.6℃条件下,将初始体质量为(3.91±0.22) g的长薄鳅幼鱼随机分为5组,每组3个重复,每个重复10尾鱼,饲养在圆形玻纤缸(直径1 m、高0.8 m)中,分别投喂刀额新对虾、鳙鱼、配合饲料(粗蛋白≥46.0%)、虾+饲料、鱼+饲料5种饵料,以筛选适宜于长薄鳅幼鱼的适宜饵料投喂模式。75 d的饲养结果表明,不同投喂模式对长薄鳅的存活率无显著性影响(P>0.05),而对长薄鳅的生长影响显著(P<0.05)。试验结果表明,虾组、鱼组、饲料组、鱼+饲料组的长薄鳅最终体质量无显著性差异(P>0.05),但虾+饲料组最终体质量和体质量特定生长率显著高于其他4组(P<0.05),依次为虾+饲料组>饲料组>虾组>鱼组、鱼+饲料组。5个试验组鱼的体长特定生长率无显著性差异(P>0.05),依次为虾+饲料组>虾组>饲料组、鱼+饲料组>鱼组。试验结束时,各试验组鱼的生长离散均有所升高,生长离散变化依次为鱼组>鱼+饲料组>饲料组>虾组>虾+饲料组。各试验组长薄鳅的的摄食率差异显著(P<0.05),摄食率依次为鱼组>虾组>鱼+饲料组>虾+饲料组>饲料组;虾组和鱼组的饵料系数无显著性差异(P>0.05),但显著高于其他3组(P<0.05),其他3组间无显著性差异(P>0.05)。不同投喂模式下长薄鳅幼鱼的生长系数b值均小于3,呈负异速生长,但虾+饲料组的长薄鳅幼鱼生长系数b值最大。试验过程中各组鱼的肥满度均下降。研究结果显示,在本试验的不同饵料投喂模式中,投喂虾+饲料更利于长薄鳅的摄食和生长。     

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.     

Apparent Digestibility Coefficients of Nutrients and Nutritional Value of Poultry By-product Meals for Rainbow Trout Oncorhynchus mykiss Measured in vivo Using Settlement

Fish meal production is not growing worldwide, therefore, it is important to search for alternative protein sources. Three types of poultry by-product meals (feed grade, prime, and refined) and two fish meals (herring and menhaden) were mixed into a casein-gelatin purified reference diet at 30% to measure apparent digestibility coefficients (ADCs) for rainbow trout Oncorhynchus mykiss . A total of 90 fish (initial mean body weight 294.6 ± 10.7 g) were stocked into six 140-L fiberglass digestibility tanks at 15 fish per tank. Individual tanks were assigned randomly to each of the five experimental diets and the reference diet. Fecal collection by settlement lasted for 2 wk. Feces collected in each week represented a replicate, and they were analyzed separately. The ADCs of nutrients for herring meal, menhaden meal, feed grade poultry by-product meal, prime poultry by-product meal, and refined poultry by-product meal were: dry matter, 81.3, 70.9, 70.9, 71.5, and 74.5%, respectively ( P = 0.0168); crude protein, 89.8, 85.8, 83.1, 84.8, and 87.1%, respectively ( P = 0.0032); crude fat, 91.5, 90.7, 79.7, 82.7, and 79.9%, respectively ( P = 0.0004); ash, 76.6, 66.2, 74.1, 77.4, and 79.6%, respectively ( P = 0.2880); phosphorus, 58.2, 46.9, 49.4, 45.8, and 56.0%, respectively ( P = 0.0143); gross energy, 88.2, 84.0, 81.9, 83.4, and 79.8%, respectively ( P = 0.2466). Significant differences in ADCs of essential amino acid existed only for arginine, leucine, and tryptophan when comparing refined poultry by-product meal with herring meal. Results showed that refined poultry by-product meal had similar ADC values to herring meal, thus, it has a similar nutritional value and can replace portions of herring meal in rainbow trout feeds. Furthermore, differences exist in ADC values among grades of poultry by-product meals that should dictate appropriate use levels in rainbow trout feeds.     

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.