Effect of meal size modulation on growth performance and feeding rhythms in European sea bass (Dicentrarchus labrax, L.)

The combined effect of feeding time and meal size on the growth performance and feeding rhythms were studied in European sea bass maintained under natural summer–autumn conditions. Three feeding strategies were compared: a modulated automatic-feeding (MF), a fixed automatic-feeding (FF) and a free access to self-feeders (SF). Under MF, feed was supplied in meals of different size, three times a day (morning, afternoon and evening, 33.33:16.67:50% of daily feed ration, respectively) during the first (31 days) and second (35 days) period of the experiment, and twice a day (morning and evening, 33.33:66.67% of daily feed ration, respectively) during the third period (27 days). In FF feed was supplied in equally-sized meals, three times a day (morning, afternoon and evening, 33.33:33.33:33.33% of daily feed ration) in all three periods of the experiment. Under SF, fish showed a diurnal self-feeding pattern, with the greatest percentage of self-feeding activity concentrated in the evening. In MF and FF, although feed was delivered automatically, the trigger was left in the tank to register activations as an indicator of feeding activity. The trigger activation of both treatments MF and FF was associated with the time of feed delivery. Feeding strategies affected biomass increase, specific growth rate (SGR) and feed conversion ratio (FCR), the greatest biomass increase and highest SGR being obtained with MF and the poorest FCR with FF. The results demonstrate that automatic-feeding systems, in which the quantity of feed supplied is modulated in accordance with the natural feeding rhythms of sea bass, may improve growth and feed efficiency.     

Daily rhythms of blood glucose differ in diurnal and nocturnal European sea bass (Dicentrarchus labrax L.) undergoing seasonal phase inversions

Sea bass change their feeding rhythms from diurnal to nocturnal in winter, returning to diurnal feeding in spring. Despite behavioral data, the physiological changes that take place during such changes remain unexplored. In this paper, blood glucose rhythms of European sea bass with diurnal/nocturnal self-feeding rhythms were investigated during phase inversions of their feeding behavior (in winter and spring) when both diurnal and nocturnal fish coexist. Blood glucose showed daily variations in both seasons (ANOVA, p < 0.03), fitting a cosine function (COSINOR, p < 0.05) in all cases, except in diurnal fish in spring. The average blood glucose levels of nocturnal fish in winter (2.67 ± 0.09 mmol/l, mean ± SEM) were significantly (t test, p < 0.01) higher than in spring (2.20 ± 0.08 mmol/l), while they were similar (~2.25 mmol/l) in diurnal fish in both seasons. These findings revealed for the first time insights into the seasonal physiological changes that accompany changes in behavioral rhythms in diurnal and nocturnal sea bass.     

Feeding Frequency Affects Growth, Not Fillet Composition, of Juvenile Sunshine Bass Morone chrysops×M. saxatilis Grown in Cages

Abstract.— In an effort to feed sunshine bass Morone chrysops × M. saxatilis efficiently, promote optimal growth, and reduce labor costs associated with feeding, sunshine bass were grown in cages and fed one of four feeding frequencies: once/d, twice/d, once every other day (I X/EOD), and twice every other day (2X/EOD) for 21 wk. Juvenile sunshine bass were fed a commercial floating diet containing 40% protein and 11.5% lipid. One hundred fish were hand-counted and stocked into each of 12 3.5-m³ cages with three replications per treatment. At the conclusion of the study, percentage weight gain of sunshine bass fed twice/d was significantly (P < 0.05) higher (1,850%) compared to fish fed all other feeding frequencies. Specific growth rate (SGR) of fish fed twice/d was significantly higher (2.1%/d) compared to fish fed all other feeding regimes, while fish fed once/d had a higher SGR (2.0%/d) compared to fish fed I X/EOD (1.6%/d) and 2X/EOD (1.8%/d). Percentage survival was not significantly different (P > 0.05) among all treatments and averaged 70.4%r. Feed conversion ratio (FCR) of fish fed twice/d was significantly higher (2.40) compared to fish fed all other feeding regimes. Percentage fillet weight of fish fed twice/d was significantly higher (27.8%) compared to all other treatments. Percentage moisture, protein, lipid, and ash in fillet were not significantly different among all treatments and averaged 75.7%, 19.4%, 3.5%, and 1.2%n, respectively (wet-weight basis). Based upon data from the present study, it appears that producers growing juvenile sunshine bass in cages may want to feed fish twice daily. This feeding regimen allows for higher growth rates, without adverse effects on body or fillet compositions. However, economic analysis needs to be conducted to determine if feeding twice/d is profitable.     

Growth,Feed Utilization,and Glycemic Response in European Sea Bass,Dicentrarchus labrax,Juveniles Fed Carbohydrate of Different Complexities

The effect of dietary carbohydrate complexity on growth, feed utilization, and glycemia was studied in European sea bass juveniles. Four isonitrogenous (50% crude protein) and isolipidic (15% crude lipids) diets were formulated to contain 20% pregelatinized maize starch (PGS diet), dextrin (DEX diet), maltose (MAL diet), or glucose (GLU diet). No effect of dietary carbohydrate complexity on growth was noticed. Feed efficiency and protein efficiency ratio were lower in fish fed the GLU diet than in the other groups, whereas the opposite was observed for feed intake. Plasma glucose peaked 3–4 h after feeding in fish fed the MAL and GLU diets, whereas in fish fed the PGS and DEX diets the peak was reached 5–6 h after feeding. Peak plasma glucose concentration (13 mmol/L) was higher in fish fed the GLU diet than the other diets (9 mmol/L). Shorter hyperglycemia duration was observed in fish fed the MALT and GLU diets (6 h) than the PGS and DEX diets (10 h). Complex carbohydrates delayed plasma glucose concentration peak compared with simple sugars, whereas the opposite was observed for hyperglycemia duration. Overall, dietary maltose, dextrin, and starch were apparently better utilized as energy source than glucose by European sea bass juveniles.     

The Effect of Partial Replacement of Dietary Fishmeal with Fermented Prawn Waste Liquor on Juvenile Sea Bass Growth

A feeding trial was conducted for 49 days to evaluate the effect of partially substituting fishmeal with fermented prawn waste liquor (FPWL) in juvenile sea bass diets at 10%, 20%, and 30% of the total diet. Growth performance of sea bass from 16 g up to 40 g fed with FPWL-supplemented diet was not significantly different from the all fishmeal control diet. The most cost-effective diet included FPWL at 30%, with weight gain, feed conversion ratio, and protein efficiency ratio of 180%, 1.78%, and 1.2% respectively.     

Modelling of surface and 3D pellet distribution in Atlantic salmon (Salmo salar L.) cages

Feed represents the greatest single cost factor in the production of Atlantic salmon (Salmo salar L.). Focusing on the problem of maximising the available feed for the fish while minimising the feed waste, a mathematical model of the feeding process has been developed. The model covers the feed spreader delivering the feed, water currents, pellet sinking speed and turbulent diffusion, fish appetite as a function of temperature, gut fullness and population structure, and is intended as a tool both for optimising general feeding strategies, and to support the daily handling of the feeding process. The process of horizontal and vertical diffusion of feed pellets in the model has been parametrised and validated through two low level validation experiments. Furthermore, global distribution patterns simulated by the model were verified by comparisons with experimental data from the literature.     

The effect of demand feeding on swimming speed and feeding responses in Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages

Abstract Using underwater cameras, data were collected on the feeding behaviour and swimming speeds of Atlantic salmon Salmo salar L., gilthead sea bream Sparus aurata L. and European sea bass Dicentrarchus labrax L. in sea cages. Comparisons were made between the behaviours of fish fed on demand using interactive feedback systems and those of fish fed under the standard feeding practice of each farm (control). In all three species, swimming speeds were similar before feeding , but they were significantly higher in the control regimes during feeding. When fed on demand, sea bass had reduced swimming speed just before and during feeding compared with that observed during the non‐feeding periods. Higher proportions of feeding fish were observed in the control regime cages than in fish fed on demand for all three species, indicating a greater feeding intensity during meals in the control regimes. This was further supported by observations of an increase in the density of sea bass in the upper water in the control cages during feeding. The results suggest decreased levels of competition between the on demand‐fed fish during feeding, which might be hypothesized to lead to improved growth and production efficiency in aquaculture.     

Feed discrimination and selection in self-fed European sea bass Dicentrarchus labrax L.

Abstract This study was conducted to evaluate feed discrimination and preference of European sea bass Dicentrarchus labrax L., taking into account the effects of feed location, previous feeding experience and light conditions. Fish (63 g) were held in tanks and exposed to a 12L:12D photoperiod and ambient temperature. The following feeding practices were applied in triplicate: three‐choice feeding (self‐ feeding with feeds formulated for carnivorous, herbivorous and omnivorous fish rotated on a weekly basis) and monofeeding (self‐feeding with one of these feeds). After 9 weeks (phase I), fish previously held in monofeeding, were subjected to three‐choice feeding for 2 weeks (phase II). In phase I, fish discriminated between feeds after their rotational displacements and preferred the feed formulated for carnivorous species. This also supported the best growth. Fish used in phase II preferred the same feed. There was no preference for any location within tanks. Feeding was generally diurnal, although in some tests with the feeds for herbivores and omnivores, diurnal and nocturnal feed demands were similar and fewer in number than with the feed formulated for carnivores.     

An acoustic based approach to evaluate the effect of different diet lengths on feeding behavior of Litopenaeus vannamei

Studying shrimp feeding behavior is challenging and, traditionally, studies have been using direct visual observation or video recordings with image analysis under laboratory conditions. Passive acoustics monitoring (PAM) is a non-invasive approach to study feeding behavior of penaeids, as their mandibles emit clicking sounds during feed ingestion. Considering the wide variation available in shrimp diet lengths, our knowledge is still limited about their effects on feeding behavior. The present study was designed to use acoustics to evaluate the feeding behavior of Litopenaeus vannamei fed different diet lengths. A commercial pelleted diet with similar diameter (2.4 mm) and three different lengths was used as treatments “small” (2.35 mm), “medium” (4.26 mm) and “large” (8.42 mm). Three separate trials were performed with fastened shrimp (20 g), using omnidirectional hydrophones and external audio recorders. Our approach started with the characterization of the click acoustic parameters produced by three shrimps when fed the different diet lengths in anechoic chambers (15 L). We then analyze the number of clicks produced per pellet and duration of the clicking activity when shrimp fed a single pellet in individual tanks (1 L). Finally, the acoustic energy of feeding activity and feed consumption, as well as theirs relationship to predict feed intake was evaluated in aquaria (70 L) with five shrimps. The acoustic parameters of isolated clicks were not affected by the different diet lengths, however, doubling the length of the pellet resulted in doubling the number of clicks emitted during feeding activity. The duration of clicking activity per pellet indicated that small pellets are consumed 2.9 and 4.7 times faster than medium and large pellets, respectively. Furthermore, feeding acoustic energy of small pellets decreased rapidly after feed offer, as their faster consumption probably contributed to shrimps achieved satiety earlier than larger diets. Feed consumption was similar among diets length, but significantly correlated with the feeding acoustic energy emitted by L. vannamei, which is a breakthrough in feeding behavioral research. The results highlight the potential and possibilities of an acoustic approach to estimate feed consumption, as well as an alternative to traditional methods in feeding behavioral studies to improve efficiency of feed management.     

Dietary Protein Requirements of Juvenile Black Sea Bass,Centropristis striata

A feeding trial was conducted in a recirculating system to determine the dietary protein requirement for juvenile black sea bass. Six isocaloric diets were formulated to contain varying levels of crude protein (CP) ranging from 36 to 56% (36, 40, 44, 48, 52, and 56%) by substituting a mixture of carbohydrates and lipid for fish meal. The feeding experiment was carried out in 18‐75 L aquaria stocked at a density of 15 juveniles (initial average weight 6.7 g) per tank. Fish were fed test diets in triplicate tanks to apparent satiation twice a day for 8 wk. Whole‐body proximate composition was analyzed after the feeding trial. After the feeding trial, weight gain and specific growth rate of fish fed the 44% CP diet were not significantly different from those fed the 48, 52, and 56% CP diets, but were significantly higher (P < 0.05) than those fed the 36 and 40% CP diets. Feed conversion efficiency and protein efficiency ratio were significantly affected by dietary protein level. The dietary requirement of protein for maximum growth of black sea bass juveniles, estimated using broken‐line regression analysis on weight gain, was 45.3% and maximum weight gain occurred at 52.6% based on polynomial regression analysis.     

利用棉籽浓缩蛋白替代条纹锯鮨饲料鱼粉的潜力

通过10周生长实验评价了利用棉籽浓缩蛋白替代条纹锯鮨饲料鱼粉的潜力。采用单因素实验设计,设4个鱼粉替代水平。对照饲料(C)中鱼粉含量为35%,通过添加棉籽浓缩蛋白分别替代饲料C中鱼粉的40%(R40)、60%(R60)和80%(R80)。每个处理设3个重复。实验鱼初始体质量为(29.5±0.5) g。实验期间,每天分2次按饱食量投喂实验饲料。结果发现,利用棉籽浓缩蛋白替代饲料鱼粉对鱼摄食、生长、饲料利用效率、鱼体组成和养殖废物(氮、磷和碳)排放量无显著影响,但单位鱼产量鱼粉消耗量(RCP)随饲料鱼粉含量下降而降低。基于生长、饲料成本、饲料利用效率、对环境的影响和RCP进行综合分析,研究表明,投喂饲料R80时的养殖效益与投喂饲料R40和R60时存在较大差异,通过添加棉籽浓缩蛋白可将条纹锯鮨饲料鱼粉含量降低至7%。     

Growth performance and feeding utilization of alternative feed for adult horseshoe crabs Carcinoscorpius rotundicauda kept in captivity

The aquafeed development has been initiated for horseshoe crabs in captivity. However, much of the attentions were to the juveniles for their widely used in research. Until recently, the research had incorporated the adult horseshoe crabs. This study aims to 1) determine the best alternative feeds for adult males of Carcinoscorpius rotundicauda, 2) measure the acceptance rate of feed, and 3) feeding utilization. Three semi‐moist pellets were either developed or purchased: fish (Decapterus russeli) and cockle (Anadara granosa) pellets (A), fish pellets (B) and keropok pellets (C). Natural feeds act as control: cockle, Anadara granosa (D) and fish, D. russeli (E). The horseshoe crabs were fed daily for 5 weeks and were analysed on their feed percentage consumption, body weight changes, feeding rate (FR), absorption efficiency (AE), feeding conversion ratio (FCR) and specific growth rate (SGR). Feed A was consumed the most (56.21%) with the highest FR (1.88%). It was influenced by the pellet's hardness, where horseshoe crabs favoured softer pellets. Body weight changes, FCR and SGR also showed a similar trend of favouring alternative feed over natural feed. Alternative feeds served a better feed than the natural feed and can be an option for future natural feed replacement for adult horseshoe crabs in captivity. Alternative feed served a better diet than the natural feed and Feed B served the best feed among the three alternative feeds with good C. rotundicauda growth performance and the feed itself is cost‐wise.     

Replacement of Fishmeal with a Blend of Poultry Byproduct Meal and Soybean Meal in Diets for Largemouth Bass,Micropterus salmoides

A feeding trial was conducted to evaluate the potential of replacing fishmeal with poultry byproduct meal (PBM) and soybean meal in diets for largemouth bass, Micropterus salmoides. A reference diet (C) contained 400 g/kg fishmeal, and 40 or 60% of the fishmeal was replaced with a blend of pet‐food‐grade PBM and soybean meal (diets PP1 and PP2) or a blend of feed‐grade PBM and soybean meal (diets PF1 and PF2). No significant differences were found in weight gain, nitrogen retention efficiency (NRE), condition factor, and body composition among fish fed diets PP1, PP2, PF1, and PF2. Feed intake and feed conversion ratio (FCR) were higher in fish fed diet PF1 than in fish fed diet PP1. No significant differences were found in weight gain, NRE, condition factor, and body composition between fish fed diet C and diets PP1, PP2, PF1, and PF2. The feed intake and FCR were lower in fish fed diet C than in fish fed diets PP2, PF1, and PF2. This study reveals that dietary fishmeal level for largemouth bass could be reduced to 160 g/kg by inclusion of PBM and soybean meal in combination.     

饲料中可消化淀粉对大口黑鲈生长、体组成和非特异性免疫指标的影响

配制6种不同可消化淀粉水平(5.93%、8.71%、11.96%、15.11%、18.16%、21.74%)的等氮和等脂肪的饲料,以试验鱼的生长、饲料效率、体组成、血糖及非特异性免疫和血液学参数作指标,评定大口黑鲈饲料中可消化淀粉的适宜水平。用上述6种饲料饲喂初始体质量(28.36 ± 0.10)g 的大口黑鲈48 d,每饲料设3个重复,每重复35尾鱼。采用表观饱食投喂,每天饲喂2次(8:00和16:00)。结果显示,饲料中可消化淀粉水平为21.74%时,大口黑鲈成活率最低;可消化淀粉水平超过8.71%时,鱼体终末体质量、特定生长率和摄食量均显著下降;但饲料效率和蛋白质效率在可消化淀粉水平为11.96%时达到最高。随着饲料中可消化淀粉水平的升高,饲料的蛋白质消化率差异不显著,但脂肪和淀粉的消化率显著降低;全鱼、肌肉、内脏及肝脏的蛋白质含量均显著降低,而水分含量显著升高,脂肪含量在8.71%组达到最高后又显著降低;肝体比、脏体比、肝糖原及血清谷丙转氨酶和谷草转氨酶的活性均显著升高。饲料中可消化淀粉水平高于11.96%时,试验鱼餐后6至12 h呈现持续的高血糖症状;血清蛋白质含量和血清补体活性在可消化淀粉为8.71%时达到最高;而血清溶菌酶活性和头肾白细胞呼吸爆发活性在11.96%组达到最高。另外,红细胞数和红细胞压积未受到饲料中可消化淀粉水平增高的显著影响,但血红蛋白含量显著降低。综合大口黑鲈的生长、饲料效率、体组成、血糖和非特异性免疫指标得出,大口黑鲈对饲料中可消化淀粉的利用与耐受力有限,饲料中可消化淀粉的适宜水平为8.71% ~ 11.96%。     

Effects of Different Feeding Frequencies on Growth,Body Composition,and Fillet Composition of Juvenile Sunshine Bass,Morone chrysops × M. saxatilis Grown Indoors

Abstract

In an effort to feed sunshine bass (Morone chrysops X M. saxatilis) efficiently, promote optimal growth, and reduce labor costs associated with feeding, sunshine bass were fed one of four feeding schedules: once per day, twice per day, once every other day, and twice every other day for 10 weeks. Ten fish were stocked into each of sixteen 110-L aquaria with four replications per treatment. At the conclusion of the feeding trial, percentage weight gain of sunshine bass fed twice/day were significantly (P < 0.05) higher (342%) compared to fish fed all other feeding frequencies. Specific growth rate (SGR) of fish fed twice/day was significantly higher (1.85%/day) compared to fish fed once every other day (0.69%/day) and twice every other day (1.18%/day) but not different (P > 0.05) from fish fed once/day (1.51%/day). The amount of diet consumed by fish fed twice/day was significantly higher (119 g diet/fish) compared to fish fed all other feeding frequencies. Feed conversion ratio (FCR) of fish fed twice/day were significantly higher (1.50) compared to fish fed once/day (1.28) and once every other day (1.15) but not different (P > 0.05) from fish fed twice every other day (1.35). Percentage fillet weight of fish fed once/day and twice/day were significantly higher (20.3% and 21.2%, respectively) compared to fish fed once every other day (15.7%) but not different from fish fed twice every other day (18.8%). Percentage lipid in fillet was not significantly different among all other treatments and averaged 9.7%. Percentage protein in fillet of fish fed once every other day and twice every other day was significantly (P > 0.05) higher (90% and 82.1%, respectively) compared to fish fed once/day and twice/day (81.1% and 81.5%, respectively). Based upon data from the present study, it appears that producers growing small juvenile sunshine bass indoors should feed fish twice daily. This feeding regimen allows for higher growth rates, without adverse effects on body or fillet compositions.     

Optimizing dietary protein sources for Japanese sea bass (Lateolabrax japonicus) with an emphasis on using poultry by‐product meal to substitute fish meal

This study evaluated the potential of using poultry by‐product meal (PBM) to replace fish meal in diets for Japanese sea bass, Lateolabrax japonicus. Fish (initial body weight 8.5 g fish^?1) were fed six isoproteic and isoenergetic diets in which fish meal level was reduced from 400 g kg^?1 (diet C) to 320 (diet PM1), 240 (diet PM2), 160 (diet PM3), 80 (diet PM4) or 0 g kg^?1 (diet PM5), using PBM as the fish meal substitute. The weight gain (WG), specific growth rate, nitrogen retention efficiency, energy retention efficiency and retention efficiency of indispensable amino acids were higher in fish fed PM1, PM2, PM3 and PM4 diets than in fish fed diets C or PM5. The phosphorus retention efficiency was lower in fish fed PM3, PM4 and PM5 diets than in fish fed C, PM1 or PM2 diets. Fish fed diet PM5 had the highest feed conversion ratio, total nitrogen waste output (TNW) and total phosphorus waste output (TPW) among the treatments. No significant differences were found in the hepatosomatic index or body contents of moisture, lipid and ash among the treatments. Fish fed diet C had lower condition factor and viscerosomatic index than those of fish fed PM1, PM3, PM4 and PM5 diets. The results of this study indicate that using fish meal and PBM in combination as the dietary protein source produced more benefits in the growth and feed utilization of Japanese sea bass than did using fish meal or PBM alone as the dietary protein source. The dietary fish meal level for Japanese sea bass can be reduced to 80 g kg^?1 if PBM is used as a fish meal substitute.     

Effects of restricted feeding on growth of red sea bream and sedimentation of aquaculture wastes

For improving the economic and environmental sustainability of fish farming, it is necessary to optimize feeding regimes. From this viewpoint, we monitored the growth and mortality of red sea bream (Pagrus major), C and N fluxes and sediment chemistry at 2 commercial fish cages; cage 1 (conventional satiation feeding) and cage 2 (restricted feeding: same feeding frequency but 18% reduction in the feed amount) for 276 days. The similar specific growth rates (0.43% in cage 1 and 0.39% in cage 2) but different feed conversion efficiencies (0.54 in cage 1 and 0.62 in cage 2) and mortality (> 2-times higher in cage 1) between the 2 cages, indicate overfeeding in cage 1 culture. Elemental and stable isotopic analyses of sediment trap materials enabled the quantification of waste feed- and fecal matter-derived organic matter (OM) separately. The results shows that (1) aquaculture-derived OM comprised most of the fish-farm settling OM, excluding the period from January to April, when natural OM often accounted for a half of the bulk OM, (2) there was a difference in the seasonal trend between the fluxes of waste feed and fecal matter, and (3) there were no differences in the percentage compositions and fluxes of waste feed and fecal matter between the 2 cages. The isotopic analysis showed that the waste feed-derived OM in the sediment below cage 2 was 24% less than that below cage 1, suggesting effect of restricted feeding. Determining the relative amount of waste feed and fecal matter in settling and sedimentary OM is an effective method to evaluate the optimum feeding regime.     

Effects of different feeding frequency on the growth, survival and feed conversion ratio of the Asian sea bass Lates calcarifer juveniles reared under hypersaline seawater of the Red Sea

The effects of several feeding frequencies of two, three and four times per day on Asian sea bass Lates calcarifer growth performance have been tested. Fish were reared under ambient Red Sea water conditions; these fish were fed diets containing 48% crude protein for 45 days. The present study was carried out at the Faculty of Marine Science (Abhor branch). The results show that fish population fed twice daily had significantly better growth with a mean body weight and daily weight increment of 59.04 and 1.31 g, respectively (P<0.05), than the other population fed three or four times daily. No significant differences were observed between fish fed two and three times daily in length gain and daily length increment. Growth in weight and length was increased gradually and no mortality was observed during the experimental period. In all the feeding trials, the body weight increased with an increase in length (R²=0.87 and 0.90). The feed conversion ratio (FCR) was significantly affected by feeding frequencies, with a significantly better FCR value of 2.43 in fish fed twice daily (P<0.05) compared with the other two populations fed three and four times daily. These results led to the conclusion that feeding two times daily would result in better growth and utilization of feed for the Asian sea bass L. calcarifer juvenile.     

Feeding activity rhythm in Japanese sea catfish <Emphasis Type="Italic">Plotosus japonicus</Emphasis>

To examine the feeding activity characteristics of Japanese sea catfish Plotosus japonicus, access to feed box (feeding activity) and the number of food pellets consumed (food intake) were recorded under laboratory conditions. When fed ad libitum under a 12:12 h light–dark (LD) cycle, all fish exhibited feeding activity and consumed food during the dark period. Feeding activity increased in the presence of food, and this increased activity level continued for several days after food removal. During restricted food availability within the light period of the LD cycle, seven of nine fish exhibited food-anticipatory activity (FAA) both before and after the 12:00 food-restricted time. This FAA persisted under constant light conditions (in nine of nine fish). The average circadian free-running period was 24 h. These results suggest that P. japonicus exhibits a nocturnal feeding activity rhythm, which may be synchronized by a food-restricted time.     

Requirement of n-3 long chain polyunsaturated fatty acids for European sea bass (Dicentrarchus labrax) juveniles: growth and fatty acid composition

European sea bass juveniles (14.4±0.1 g mean weight) were fed diets containing different levels of fish oil then of n-3 highly unsaturated fatty acids (n-3 HUFA) for 12 weeks. The fish performance as well as fatty acid (FA) composition of neutral and polar lipids from whole body after 7 and 12 weeks feeding were studied. The requirements of juvenile sea bass for n-3 highly unsaturated fatty acids (n-3 HUFA) were studied by feeding fish diets containing six different levels of n-3 HUFA ranging from 0.2% to 1.9% of the diet, with approximately the same DHA/EPA ratio (1.5:1).

The growth rate at the end of the trial showed significant differences. Fish fed low dietary n-3 HUFA (0.2% DM of the diet) showed significantly lower growth than the diet 3 (0.7%), then no further improvement (P>0.05) of growth performance was seen by elevating the n-3 HUFA level in the diet up to 1.9% (diet 6). No difference in feed efficiency, protein efficiency ratio or protein retention was observed among treatments, nor in protein and total lipid content. However, the n-3 HUFA levels in diets highly influenced fish fatty acid composition in neutral lipid, while polar lipid composition was less affected. Comparison of polar lipid content after 7 or 12 weeks indicated that DHA remained stable at the requirement level, while arachidonic acid decreased with time. Results of this experiment suggest that the requirement for growth of n-3 HUFA of juvenile sea bass of 14 g weight is at least 0.7% of the dry diet.