Growth induction of common carp, Cyprinus carpio L., fry as a function of plankton density and improved water quality

Abstract. One hundred and ninety-eight fry of common carp, Cyprinus carpio L., were reared in outdoor tanks containing 9580 1 of water under five management schemes — separate live-food system (LF), intermediate system (I), static manured system (M), manured system with water exchange (EM) and supplementary food system (SF) — in triplicate for a growing period of 90 days. Examination of frequency distribution of different weight groups of fishes at the time of harvest showed a maximum proportion of larger and smaller fishes in the live-food and supplementary food system, respectively. Maximum growth and production of common carp in the LF treatment was the consequence of greater abundance of plankton food and improvement of water quality expressed in terms of higher values of pH and DO and lower values of COD and BOD.     

Optimum food particle size in relation to body size of common carp, Cyprinus carpio L., fry

Abstract. An investigation was conducted under laboratory conditions to determine the optimum food particle size of an inert diet for common carp fry ranging in size from 15 to 466mg body weight and 13 to 31 mm total length (TL). Speed of consumption of a standard quantity of food was used as a measurement of feeding preference/efficiency for different particle size ranges. It was observed that for carp of this size range preferred food particle size increases with fish size. On the basis of ingestion time and feeding behaviour, food particle sizes in the ranges 125-300μm. 300-500μm, 300-790μm and 500-1000μm diameter were found to be most appropriate for carp fry weighing 15-23mg(TL 13-18), 46-97 mg(TL 17-22), 105-209 mg (TL 20-25) and 210-466mg (TL 24-31) respectively. This study also demonstrated that for carp fry of these size ranges the mean preferred food particle sizes are about 02-04 that of mouth size. Based on this relationship, general recommendations are made on the optimum food particle sizes for different size classes of carp fry reared under hatchery and nursery conditions.     

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) ×Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

The effects of four levels of food supply (0.5%, 1%, 2% and 3% body weight daily) were investigated on some reproductive traits and growth of hybrid tilapia in outdoor concrete tanks. Fast-growing fish matured early in the season (March), but spawning started late in May. Smallest size of males and females at first maturity was 8.1 cm. Fish size at maturity appears to be influenced by the feeding level, which affects the growth of fish. For both sexes, no significant difference was found in gonadosomatic index (GSI) among different treatments. Mean percentage of mature fish decreased with decreasing food supply and was found to be significantly different between fishes fed at 3% (46%) and 0.5% (28%) body weight. Fecundity increased with increased feeding levels, although significant differences were found only between 3% and other feeding rates (0.5–2.0%). The fecundity per g female was higher at the lower ration levels (0.5% and 1%) than at the higher feeding levels. Egg quality, with respect to egg size, hatchability. fry length and weight, was not affected by the feeding rates. Final mean weight and food conversion ratios were significantly influenced by feeding rates. Higher increase in ovary weight with increasing body weight of mature females fed at 0.5% body weight than fishes receiving higher food levels suggests that in these fish, more food resources are diverted towards gonad building than to somatic growth.     

膨化与非膨化饲料对大规格草鱼生长、体成分及部分生理生化指标影响

以商业配方为基础,配制膨化饲料和非膨化饲料饲喂初始体重（394.96±13.21g）草鱼（Ctenopharynodon idellus）120天,旨在对比这两种饲料对其生长、体成分及部分生理生化指标的影响。养殖试验在水库网箱（2m×2m×2m）中进行,每个处理组3个重复,每个重复30尾鱼。实验结果表明,与非膨化料组相比,膨化饲料组草鱼成活率和增重率显著提高（P＜0.05）,饵料系数显著降低（P＜0.05）,增重成本显著降低（P＜0.05）;肥满度、肝体比、脏体比和肠体比显著升高（P＜0.05）;鱼体血清血糖、甘油三酯、总固醇和过氧化氢酶显著升高（P＜0.05）;胰蛋白酶、淀粉酶和脂肪酶显著降低（P＜0.05）;肝脏谷丙转氨酶（GPT）显著升高,谷草转氨酶（GOT）显著降低（P＜0.05）;鱼体成分中水分和灰分无显著差异（P>0.05）,粗脂肪显著升高、粗蛋白显著降低（P＜0.05）。综上所述,与非膨化饲料相比,饲喂膨化饲料可使大规格草鱼生长性能和养殖效益提高,但会鱼体肥满度和粗脂肪含量提高。     

A comparison of growth, survival rate and number of marketable koi carp produced under different management regimes in earthen ponds and concrete tanks

To compare the growth performance of koi carp, Cyprinus carpio var. koi, produced in concrete tanks (2.13 × 0.91 × 1.22 m; capacity: 2,000 l each) and earthen ponds (9.1 × 6.10 × 1.07 m; capacity: 59650 l each), fish larvae (stocking size: 0.12 ± 0.008 g) were cultured for 11 weeks and individual weight gain, survival rate and number of marketable fish produced were compared among four management regimes for each culture system: (1) live zooplankton fed to fish larvae in ponds (PLF) and tanks (TLF); (2) application of poultry manure in ponds (PPM) and tanks (TPM); (3) application of cow manure in ponds (PCD) and tanks (TCD); and (4) a control treatment for ponds (PC) and tanks (TC), where a commercial feed was applied. There were three replicates for each treatment. Weight gain of koi carp was highest in the PLF treatment, followed in decreasing order by TLF, PPM, PCD, TPM, TCD, PC and TC treatments (P < 0.05). There was a significant difference in the survival of koi carp among the treatments, ranging from 67.83% in TC to 95.50% in PLF. The number of marketable fish produced was highest in the PLF treatment, followed in decreasing order by TLF, PPM and PCD treatments. However, none of the fish produced in the TPM, TCD, PC and TC treatments attained marketable size. Significantly higher (P < 0.05) values of pH and dissolved oxygen (for water samples collected weekly at 9 A.M.) were obtained in the live food and control treatments (for both tanks and ponds), compared to the manured treatments. The concentration of total alkalinity, BOD, PO₄-P, NO₃-N and specific conductivity were significantly higher (P < 0.05) in PPM and PCD, compared to other treatments. NO₂-N and NH₄-N values were significantly higher (P < 0.05) in TPM and TCD, than other treatments. The results suggest that introduction of live zooplankton into culture units result in higher growth of koi carp larvae compared to manure based systems. Earthen ponds appeared to be better alternative to concrete tanks for manure application through maintenance of better water quality due to their higher assimilatory capacity and greater abundance of plankton which resulted in better growth of cultured fish.     

Effect of density on survival and growth of cyprinid fish fry

One of the bottlenecks in Israel's cold water ornamental fish industry is the large loss of fish during the post-larval stage. As a first step towards increasing survival rates, the optimal stocking density in earthen ponds for fry of each species should be determined. The results of five consecutive experiments with fry of goldfish (Carassius auratus), common carp and koi (respectively, edible and ornamental morphotypes of Cyprinus carpio) are presented here. The experiments were run in 18 cages of 1 m³ and 0.8 mm mesh size placed in a 0.02 ha earthen pond, stocked at 50,100 and 200 fry per cage. The variables analyzed were growth rate, harvesting weight, biomass and survival. Equations to estimate growth rates under different conditions are given. The three fish types present different growth rates and survival patterns in relation to stocking density and season, which lead to different management implications. Koi can be stocked up to 2 million fry per ha without showing negative density effects. Goldfish should be stocked at low density (500,000–1 million fry per ha) in spring and at higher rate (2 million fry per ha) in summer. Common carp stocking density should be adjusted to obtain the required fish size at harvest.     

Grass carp (Ctenopharyngodon idella) grazing on duckweed (Spirodela polyrhiza)

The aims of this experiment were (1) toquantify the ability of grass carp to processduckweed and (2) to assess indirect changes inwater chemistry and phytoplankton community,caused by grass carp feeding. Yearling grass carp sized 126 ± 7.7 mm (TL) and19.6 g in weight were kept in 9 laminate tanksof 1 m³ for 14 days. Two stockingdensities (2 and 6 fish per m³) anda control without fish were used. Standard growthrate (SGR) of grass carp fed exclusively onduckweed was 0.70% body weight (BW) d^–1and food conversion ratio (FCR) reached 2.0(average water temperature =21.1 ± 3.8 °C). Daily food intakewas 0.2 g of duckweed dry weight (DW), i.e.,1% of average BW of grass carp. SGR ofduckweed growing in 20 × 20 cm floatingenclosures, differed significantly[F(6,2) = 417.9; p = 0.002] between the twostocking densities of grass carp and thecontrol tanks (without fish). Mean SGR ofduckweed was 0.02 g g^–1 day^–1 and thehighest SGR was recorded in the control tanks.Both decrease in NH₄-N and increase inNO₂-N concentrations differedsignificantly between the treatments[F(2,2) = 45.3; p = 0.02 and F(2,2) = 19.2; p = 0.04 respectively]. Changes in other nitrogenand phosphorus components (NO₃-N, TN, TPand PO₄-P) caused by stocking of grasscarp were not significant. Biomass ofphytoplankton, dominated by filamentous algaeand blue-greens, increased proportionately tostocking density of grass carp. Althoughduckweed has a large potential for nutrientremoval, the most common pathway for thenutrients released through grass carp grazingif duckweed cover is loose is theirincorporation into phytoplankton biomass.     

Effects of silver carp and the small indigenous fish mola Amblypharyngodon mola and punti Puntius sophore on fish polyculture production

A sustainable semi-intensive pond aquaculture technology including major carp species as cash-crop and small indigenous fish species (SIS) as food for the farmers' families is being optimized in Bangladesh. The inclusion of silver carp (Hypophthalmichthys molitrix), a cheap large species affordable by poor farmers, is now being considered. As part of a study on the effects of this filter feeder on polycultures including the large carps rohu (Labeo rohita), catla (Catla catla) and common carp (Cyprinus carpio) and the SIS punti (Puntius sophore) and mola (Amblypharyngodon mola), an experiment was carried out under farm conditions to test the effects of silver carp and of each SIS species on the growth, survival and yield of the large and small species and on pond ecology.The experiment was performed in 38 farmers' fishponds of different sizes, from 220 m² to 1200 m². The results show that the larger the fish pond the better rohu performance, the larger punti fry weight and the lower punti fry harvested biomass. Pond size did not affect other fish species. The addition of 250 mola and/or punti per 100 m² fishponds affected rohu and catla and did not affect common and silver carps. The addition of mola alone reduced rohu's parameters by 15%. The addition of SIS in the three combinations tested (250 mola, 250 punti, 125 of each species) reduced catla's parameters by 20-24%. Punti fry were larger when both SIS were stocked and punti fry biomass was larger when only punti were present. Total mola harvested biomass and yield were larger when the entire SIS stocked were only mola.The addition of 10 silver carp over the 99 large carps stocked per 100 m² fishponds negatively affected rohu and catla growth and yield by about 15-21% and 45-50% respectively but not their survival, did not affect common carp performance, did not affect punti and mola reproduction in the ponds, reduced punti yields by 25%, reduced mola performance by about 35%, and silver carp own biomass increased total yield and total income in about 12% each. These effects are explained and discussed considering fish interactions through the food web. The decreased income from selling the more expensive large carps is more than compensated by that obtained from silver carp, which allows the option to the farmer to sell part of the silver carp to complete the cash income that would have been obtained from large carps only if silver carp would not be stocked, and consume the rest with the family.     

Development of new self-feeding system for mass rearing of ayu <Emphasis Type="Italic">Plecoglossus altivelis altivelis</Emphasis> under artificial and natural light-dark cycles

Self-feeding of grouped ayu Plecoglossus altivelis altivelis was examined under an artificial light-dark (LD) cycle and natural day length using a trigger with a photosensitive sensor. In Experiment 1, approximately 15 juvenile fish (mean body weight, 0.6 g) were kept in 60-L glass tanks (four tanks) under LD 12∶12 (lighting period 06∶00–18∶00 hours) and self-feeding and locomotor activities were simultaneously recorded. Self-feeding was detected within one day and feeding activities were strongly synchronized to the LD cycle, with almost strictly diurnal feeding (98.2%). Although locomotor activities in the upper part of the tank were also greatest during the light phase (76.8%), the activity profiles were different from those of self-feeding, suggesting the validity of the photosensitive sensor. In Experiment 2,25 fish (mean body weight, 15 g) were kept in outdoor 1000-L tanks (four tanks) under natural day length and water temperatures in May, and self-feeding was recorded from mid-August. Stable self-feeding was observed from early September in all the tanks. Nearly all food demands were diurnal, and usually crepuscular. Somatic growth was seen in all tanks. These results demonstrate that the self-feeding system using a photosensitive sensor is applicable for grouped juvenile ayu as small as 0.6 g and adult fish reared under natural conditions.     

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.     

Relative growth,survival and harvestability of bighead carp,silver carp,and their reciprocal hybrids

Growth and survival in the primary rearing phase (42 days) for bighead carp, silver carp, bighead × silver carp (BHC × SC), and silver × bighead carp (SC × BHC) in ponds and concrete tanks stocked at 370 500 fry/ha were studied. Mean survival for fishes in ponds was 93%, that in tanks was 73%. Yields among all fishes averaged 338 kg/ha. The growth rates of fishes in ponds were similar; in tanks, silver carp grew faster than the bighead carp.Growth, survival, and harvestability by seine during the secondary rearing phase (60-day duration) for the same groups of fish were studied. Fingerlings (0.9 g mean weight) were stocked in earthen ponds at 49 400 fish/ha and 98 800 fish/ha. Mean survival of fishes at low stocking rate was 77%, similar to that (71%) for the high stocking rate. Fish yields were similar at the low stocking rate. At the high rate, the BHC × SC yield (846 kg/ha) was greater than the SC × BHC yield (582 kg/ha). The BHC × SC and SC × BHC had greater mean weights at low stocking rate than at high stocking rate. The mean weights for bighead carp were similar at both rates. Bighead carp and the reciprocal hybrids were more easily harvested by seine than silver carp.     

Herpesvirus cyprini: lethality and oncogenicity

Abstract. Cyprinid herpesvirus 1 (CHV) or Herpesvirus cyprini was virulent for carp, Cyprinus carpio L., fry following 1 h immersion in water at 20 °C. Cumulative mortality for carp fry was 86–97% in 2-week-old common carp, 20% in 4-week-old fancy carp, and 0% in both 8-week-old common and fancy carp. The virus did not produce mortality in fry of crucian carp, grass carp or other cyprinids. It was also oncogenic in carp, inducing papillomas to the extent of 55% among both common and fancy carp fry. The neoplasms appeared 5–6 months after carp had been exposed to the virus by immersion and recurred at an incidence of 83% in carp 7·5 months post-desquamation of the tumour. The CHV was reisolated from all moribund fish and from all survivors. It also induced papillomas at an incidence of 13% in adult mirror carp and at 10% in adult fancy carp 5 months after intraperitoneal inoculation of 10⁵ TCID₅₀ ml^-1 fish. The virus was rcisolated only from the ncoplastic tissue and not from internal organs. The neoplasms were normally located on fin, skin or mandible, at the intraperitoneal inoculation site. Specific fluorescence for CHV antigen was frequently detected in the gills, liver, kidneys and intestine of 2-week-old fry from 3 to 21 days following challenge with CHV. It was found in greater concentrations in experimentally induced papillomata on 2-week-old carp fry survivors examined 24 weeks after challenge than in naturally occurring neoplasms.     

Impacts of domestication on angling vulnerability of common carp,Cyprinus carpio: the role of learning,foraging behaviour and food preferences

Domestication in fish selection increases vulnerability to angling. Two common garden‐reared genotypes of common carp, Cyprinus carpio L., differing in degree of domestication (highly domesticated mirror carp and less domesticated scaled carp) were exposed to fishing in two environments (i.e. ponds and laboratory tanks) to quantify vulnerability to angling. Foraging behaviour and food preferences were quantified to explain variation in angling vulnerability in a mechanistic manner. Domesticated mirror carp were more vulnerable to angling gear than scaled carp in both environments, which was related to greater food intake and bolder‐foraging behaviour. Independent of genotype, catchability decreased and time until first capture increased over fishing time, indicating learned hook avoidance. No differences were observed in food preferences among genotypes, rendering bait‐selective feeding an unlikely explanation for differential vulnerability to angling. It was concluded that vulnerability to angling has a genetic basis in carp and that boldness plays a paramount role in explaining why more domesticated genotypes are more easily captured by angling.     

Effects of feeding rates on growth and production of Nile tilapia, common carp and silver carp polycultured in fertilized ponds

Abstract In an attempt to identify appropriate feeding rates for multispecies of fish raised in fertilized earthen ponds, the present work was conducted over a 19‐week experimental period to establish the growth performance, production and body composition of Nile tilapia, common carp and silver carp fed 0.0%, 0.5%, 1.0%, 3.0%, 5.0% biomass and to apparent satiation (treatments). Twelve ponds were stocked with a similar number and weight of each fish species. Two ponds were assigned to each of the treatments, and a 25% protein pelleted fish feed was used to feed fish at the specified rate of feeding. At the end of the experiment, growth, weight gain, survival, yield and body composition of fish groups were affected by the treatments. The economic effectiveness also varied among treatments. The most conspicuous attribute of the feeding rates was its lack of influence on growth (g day^?1), weight gain (g per fish), yield (kg ha^?1) or body composition of silver carp. The results of whole‐body proximate analysis indicated that various feeding rates had either an irregular pattern or no effects on the protein and ash gain per 100 g of fish body weight (bw) gain. The most notable exceptions were significant (P < 0.05) increases in body fat and gross energy gains in Nile tilapia, common carp and silver carp accompanied by decreases in percentages of moisture (but not in silver carp) as feeding rate increased. Among the six different feeding levels, feeding to apparent satiation (feed amount was equivalent to 2.67% of fish bw day^?1) appeared to be optimal, as it significantly (P < 0.05) supported the highest fish production, income and net profit compared with all other treatments except for the 3% feeding level, for which the differences in those measurements were comparable.     

Combined effects of fertilization rate, manuring and feed pellet application on fish performance and water quality in polyculture ponds

This study analyses the combined effects of organic and inorganic fertilization and of feeding with pellets on fish performance and water quality in a polyculture of common carp. Cyprinus Carpio L., silver carp. Hypophthalmichthys molitrix (Val.), grass carp. Ctenopharyngodon idella (Val.) and hybrid tilapia, Oreochromis niloticus L. x O. aureus Stetndachner. Experiments included six treatments, which are combinations of inorganic fertilisation (daily or fortnightly), manuring (supplied or not), feed pellets (supplied or not) and density of phytoplanktivorous fish species (high-density treatments with 50% more hybrid tilapia and 300% more silver carp than low-density treatments). The effects of the management procedures on fish weight, growth, survival and yield. plankton abundance, water quality, and their complex interactions at the different levels of the natural food web were analysed. The hypothesis that daily fertilization should increase algal production, which in turn should sustain a higher density of phytoplanktivorous fish, proved to be correct within certain limits. Algal reproduction rate was higher under daily fertilization, pointing to better supply of food for herbivorous fish, while algal biomass was similar under both fertilization regimes, pointing to the utilization of that algal food supply. The increased algal food supply sustained a 50% density increase of the omnivorous tilapia, but not the 300% density increase of the grazer silver carp.     

Culture of the guppy, Poecilia reticulata, in Singapore

Singapore is known internationally as a breeding centre for the guppy, Poecilia reticulata. About 30 domesticated colour pattern and tail shape varieties are reared, mainly for export. The culture of these varieties at two rural and eight resettled farms is described. All farms are small family concerns. The resettled farms practise monoculture of guppies while the rural ones integrated farming. Guppies are reared in large, shallow, outdoor, cement tanks and nylon cage-nets suspended in ponds. Water in aquaria and ponds has salinities from 0.5 to 9.0‰, at neutral or alkaline pH of 7.0 to 8.3. The sizes and stocking densities of aquaria and nets vary within and between farms. In breeding tanks, a male to female sex ratio of 1:3, 1:4 or 1:10 is maintained. Newborn fry are collected daily and placed in nursery aquaria. After 3 weeks, these fry are sexed: young males are transferred to grow-out cement tanks, and females to grow-out cagenets. Each farm has at least two ponds, one for water storage and the others for cagenet culture. Strains are cultured separately to maintain pure lines. Farmers improve colour patterns, size and fin shapes of the strains by continued mass selection. Four- to 6-month-old guppies are selected as brookstock and the rest which meet export quality are held in stocking aquaria and sold when demand arises.Each farmer prepares his own formulated diet for the fish. Supplemental foods like live tubificiids, commercial dried fish flakes, or floating pellets may be given to adults, and water fleas to fry. The rural farms add pig manure to fertilise the tanks.To remain viable in the future, farmers need to increase productivity by mechanising cleaning, draining, and filling tanks and ponds, feeding, and harvesting of the fish. This will cut down on labour and its increasing cost. Understanding the genetics of economically important characters will also help farmers produce higher quality and more exotic strains.     

Further studies on the use of mixed feeding schedules with plant- and animal-based diets for common carp Cyprinus carpio (Linnaeus)

A growth trial was conducted on common carp Cyprinus carpio (L.) fry in cement tanks for 100 days in order to test the efficacy of mixed feeding schedules. The diets tested were a fishmeal‐based diet (diet D with 30.9% protein) and three Colocasia esculenta‐based diets (diet A with 16.7% protein, diet B with 19.7% protein and diet C with 25.8% protein) separately and in three mixed feeding combinations of diet A, B and C with D on alternate 2 days (2A/2D, 2B/2D and 2C/2D, where the numeral indicates the number of days that the particular diet was offered continuously). The results revealed no difference in growth of common carp fed the plant protein‐based diets A and B (P > 0.05). Although the fish fed on diets C and D and mixed feeding combinations 2A/2D and 2B/2D performed comparably and higher than those on diets A and B, the schedule 2C/2D resulted in the highest final weight. Specific growth rate, feed conversion ratio and RNA/DNA ratios were the highest in the 2C/2D schedule. Among the mixed feeding schedules, the highest saving in protein and cost was recorded with the 2A/2D schedule, followed by 2B/2D and 2C/2D. An increase in dietary protein led to decreased protein and increased fat deposition in the carcass. An increasing trend in the protease and amylase activities was recorded with increased dietary protein level. The study highlighted the efficient utilization of plant proteins by common carp under mixed feeding schedules.     

Evaluation of live duckweed,Wolffia globosa as an allochthonous feed for Labeo rohita fry during nursery rearing

A 40 days feeding trial with Labeo rohita (rohu) fry was conducted in six outdoor cemented tanks (5m × 4m × 1 m; 6–8 cm soil base) to establish the relative impact of on‐farm grown live Wolffia globosa (a duckweed with crude protein of 28.57%) and a formulated iso‐nitrogenous feed (crude protein 28.37%) on growth performance, survival, health and overall quality of fingerlings. The experimental tanks were dried, limed at 250 kg/ha, filled with ground water and subsequently applied with cow dung (soaked overnight) and mustard oil cake at 1,000 kg/ha and 50 kg/ha respectively. The fry were stocked at 0.3 millions/ha in six prepared tanks, and fed live Wolffia (T1) and formulated feed (T2). Results of the study indicate better performance (p < 0.05) of fry in terms of final mean weight (7.83 g), length (8.82 cm), daily growth index (6.51 g %/day) and survival (89.5%) than those fed on formulated feed. Furthermore, significantly improved (p < 0.05) feed utilization parameters viz. apparent feed conversion ratio (AFCR), apparent protein conversion efficiency (APCE), apparent protein efficiency ratio (APER); haematological parameters viz. total erythrocyte count (TEC), total leucocyte count (TLC), packed cell volume (PCV), plasma glucose and protein of fry were also observed in T1 (live Wolffia). Overall findings from this study hints towards the possible utilization of on‐farm grown live Wolffia as a suitable nutrient source for fry rearing of L. rohita.     

Carp feeding activity and habitat utilisation in relation to supplementary feeding in a semi-intensive aquaculture pond

A combination of radio telemetry and electrofishing was used to assess seasonal feeding activity and habitat utilisation of common carp (Cyprinus carpio) in a large (130 ha) semi-intensive aquaculture pond receiving supplementary feed. While telemetry indicated no difference in fish habitat utilisation by size, age or sample year, all fish showed a strong preference for the supplementary feed area (SFA) during the feeding period, electrofishing indicating a 15× higher fish concentration. Despite this, not all of the feed provided was eaten immediately. Carp activity was more evenly spread over the pond in summer/autumn and more concentrated at the SFA in spring. There was a significant shift to deeper waters in winter. Diet analysis indicated a high preponderance of cereal in SFA fish, with natural food (mainly zooplankton) dominant at natural feeding areas. The proportion of ‘emergency’ food (e.g. detritus) was similar in both areas, as was the index of gut fullness. Our results confirm that concentrated and repeated supplementary feeding in one area results in aggregation of carp, potentially leading to uneven population growth and flesh quality and reduced water quality from turbidity and increased nutrient input. As an alternative, we suggest spreading less supplemental feed over a greater area at wider time intervals. This would ensure (a) full utilisation of feed, reducing costs and increasing water quality, and (b) more homogenous fish distribution, ensuring more efficient use of natural food, reduced turbidity, more homogenous size/weight distribution and improved product quality.     

Effect of Continuous Food Supply on the Oxygen Consumption of Young Mediterranean Yellowtail (Seriola dumerili Risso, 1810)

The aim of this work was to investigate the effect of a continuous food supply on the oxygen consumption of young Mediterranean yellowtails (Seriola dumerili Risso, 1810) during the photophase period (14LL:10DD). Four groups with six fish each, weighing individually approx. 600 g, were distributed into open 2 m³ quadrangular fibreglass tanks, and fed with commercial pellets for 60 days. Two of the tanks received a continuous feed supply by means of automatic band feeders (ABF), whilst fish in the other two tanks were fed by hand, twice a day. To improve accuracy in calculating oxygen consumption, the effect of oxygen diffusion between the air and the water was determined by the use of a control tank of similar characteristics, containing no fish. Oxygen consumption instantaneous rate was calculated by the difference between dissolved oxygen concentrations in tanks with and without fish, multiplied by the water flow and divided by the estimated total fish biomass in each tank. In both feeding regimes, an increase in the oxygen consumption levels after feeding commencement was observed. The amplitude, however, was lower and the duration of feeding effect was higher in the group fed by ABF.