Effect of Dietary Lipid Level and Feeding Frequency on the Growth,Feed Utilization,and Body Composition of Juvenile Spotted Seabass,Lateolabrax maculatus

A 6‐wk feeding trial was conducted to evaluate the effects of different dietary lipid levels and feeding frequencies on the growth performance, feed utilization, and body composition of juvenile spotted seabass, Lateolabrax maculatus. Two experimental diets were prepared with two different dietary lipid contents, low lipid (7%; LL) and high lipid (14%; HL). Each diet was fed to triplicate groups of fish (5.5 ± 0.01 g) to apparent satiation at three meals per day, two meals per day, one meal per day, and one meal every 2 d, respectively, for 6 wk. Fish growth performance in terms of weight gain (WG) and specific growth rate (SGR) was significantly affected by frequency of feeding, with increasing values as feeding frequency increased up to twice daily, regardless of dietary lipid content. In addition, fish fed the diet with the HL level (14%) showed significantly higher WG and SGR than those fed the LL diet (7%) at all the feeding frequencies tested. Feed efficiency (FE) and protein efficiency ratio (PER) were affected by both dietary lipid level and feeding frequency. FE and PER values were significantly higher in fish fed the HL diet and/or when fish were fed twice or thrice a day. However, daily feed intake and daily energy intake were significantly affected only by feeding frequency and were significantly reduced when the fish were fed only once every 2 d compared with those fed more frequently. Whole‐body moisture content of fish tended to decrease with increasing dietary lipid level and frequency of feeding. In contrast, whole‐body lipid content increased in fish as dietary lipid level and feeding frequency increased. Consequently, we can conclude that feeding spotted seabass twice daily to apparent satiation is acceptable and sufficient to achieve good growth and FE, as fish performance was not significantly enhanced when feeding was increased from two to three times daily.     

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.     

Differences in growth and chemical composition between male and female farmed cod (Gadus morhua) throughout a maturation cycle

The growth of farmed cod fed to satiation under natural conditions in the sea in North Norway (67°N) was followed over 1 year. At the start of the experiment in September 2003, the average weight was 1300 g. After 1 year, in September 2004, the average weight was 2800 g. From the end of November to June, the fish matured and spawned and there was little or no weight gain in the fish during this time. The male cod developed gonads earlier than the females. In February, the male gonad index was 19% and decreased to 7% by the end of April, whereas the female gonad index increased from 14% in February to 25% in April. The male liver index decreased by 2% in February and by another 3% in April, when it only decreased by 1% in the female cod. The muscle protein in the female cod was reduced by more than 20 g kg^?1 in April, and the difference between the muscle protein in the male and the female cod was still significant in September. No differences were found in the post‐rigour muscle pH due to the sex of the fish.     

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.     

Vertical distribution and sexual maturation in cage‐farming of Atlantic cod (Gadus morhua L.) exposed to natural or continuous light

The vertical distribution and seasonal timing of sexual maturation were investigated in Atlantic cod in four large commercial sea cages in Northern Norway during their second year of on‐growth. Replicate cages were exposed to either natural light (NL) or continuous light (LL) from May 2007 to January 2008. Hydro‐acoustic monitoring revealed that the cod in the NL cages were mainly distributed from 5 to 13 m depth at day while they were more dispersed and swam deeper at night. A clear ascent was observed prior to feeding events. The cod in the LL cages displayed a similar seasonal and daily pattern, but with a more dispersed vertical distribution range at both day and night. It is hypothesized that surface feeding motivation resulted in cod preferentially occupying the upper reaches of the sea cage, generally at depths < 13 m. This would also reduce the need for excessive alterations in swim bladder volume. Both the LL and the NL groups were exposed to LL the year before the study, resulting in first time sexual maturation (puberty) being delayed until the summer in both groups. However, while cod in the NL cages matured during the autumn 2007, the LL cod did not.     

Reduction of early sexual maturation in male S0 Atlantic salmon (Salmo salar L.) by dietary supplementation of tetradecylthioacetic acid (TTA)

Effects of dietary tetradecylthioacetic fatty acid (TTA) on muscle fat, development of gonads and early sexual maturation in S0 Atlantic salmon during the first year in sea were investigated. TTA (0.5% w/w) was added to the feeds for 8 weeks in the spring. In May, at the end of the TTA‐feeding period, the fish in the TTA group had significantly (P < 0.05) less fat (10.1%) stored in muscle compared with the control group (10.8%). In September, mean male gonadosomatic index (GSI) in maturing fish in the TTA group was found to be lower compared with the maturing fish in the control group (P = 0.05). On the basis of GSI values, male sexual maturation in September was 10.0% vs. 14.4% for the TTA and the control group respectively. Thus, relative to the control group, the incidence of male sexual maturation in the TTA group was reduced by about 1/3 (P = 0.002). Production data was not affected by dietary supplementation of TTA. This study reveals that TTA significantly reduces the incidence of male sexual maturation in S0 Atlantic salmon. A significant elimination model of TTA in fish muscle that takes into account, the growth rate of the fish was further developed in this study.     

Effects of starvation,subsequent feeding and photoperiod on flesh quality in farmed cod (Gadus morhua)

The study was designed to investigate the effect of four cycles of 5 weeks starvation followed by 10‐week refeeding compared with daily feeding under either natural photoperiod or continuous light (LL) regime on body composition and flesh quality in Atlantic cod in sea cages, northern Norway. The fish were sampled for body composition and flesh quality parameters at the start of the trial, twice at the end of a 10‐week feeding period and twice at the end of a 5‐week starvation period. There was effect of both feeding and light regime on growth, the two starving groups losing weight during starvation and regaining weight during refeeding, and the group under LL being heavier. But, the mean overall growth did not vary between groups. Starvation/refeeding regime resulted in higher slaughter yield, but no overall effect was seen on hepatosomatic index, water content, water holding capacity (WHC), muscle pH, hardness or flesh colour compared with control groups. Continuous light increased gutted weight and slaughter yield, lowered WHC and depressed maturation compared with fish under natural light regime. Increased growth rate resulted in softer fillets and lower muscle pH.     

Performance of murray cod, Maccullochella peelii peelii (Mitchell) in response to different feeding schedules

The Australian freshwater fish Murray cod, Maccullochella peelii peelii (Mitchell) is gaining popularity as a suitable species for intensive culture, particularly in closed systems. The aim of this study was to evaluate the performance of Murray cod in response to different feeding schedules. Growth, survival, food conversion and a range of other related parameters including carcass proximate composition were evaluated for fish in five feed management regimes. The feeding regimes used in the experiment were hand fed to satiation twice daily (SAT), a pre‐determined ration of 1.2% of the body weight day^?1 which was hand fed twice daily (HFR), and belt fed through the day only (B/D), belt fed through the night only (B/N) and belt fed for 24 h (B/DN). Each of the five feeding regimes was randomly allocated to three tanks (triplicates). All of the feeding regimes used a commercially prepared diet formulated specifically for Murray cod, containing ≈50% protein and ≈16% lipid. The experiment was conducted for 84 days. Specific growth rate ranged from 0.89±0.01 to 1.07±0.04% day^?1. Food conversion ratio (FCR) ranged from 1.09±0.02 to 0.92±0.03. The fastest growth and greatest final body weight were observed in the SAT treatment; however, the highest FCR, visceral fat index (VFI %) and hepatosomatic index (HSI %) were also observed in this treatment. Significant differences were found in specific growth rate and final mean weight between fish in the B/D and SAT treatments. B/N and B/DN feeding regimes appeared to result in the most favourable fish performance.     

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.     

Growth of Juvenile Scup,Stenotomus chrysops,Fed Three Commercial Diets

Juvenile scup, Stenotomus chrysops, 0.5–1.5 g weight were fed three different commercial diets for six weeks to determine growth rates. Diets were hand-distributed to triplicate groups of 30 fish, four times a day. Survival for all treatments was 93%. The diets used were INVE Aquaculture NRD marine diet (NRD), Skretting Feed Products Gemma starter feed (Gemma), and Salt Creek Progression fish starter diet (Progression). While all diets supported good growth, after 6 weeks scup fed the NRD diet were of significantly greater length and weight (P?<?0.05) than fish fed the other diets. The effects of each diet on fish growth were significantly different from each other (P?<?0.05), with final live weight (g), total length (mm), relative growth rate (RGR), and daily weight gain (DWG) measurements higher for fish fed the NRD diet. Scup fed the Gemma diet were of significantly greater length and weight than fish fed the Progression diet. The specific growth rate (SGR) of scup fed either the NRD or Gemma diets were not significantly different; however, both of these diets produced fish with significantly higher SGR than those fed the Progression diet. Feed conversion ratios (FCR) of scup fed either the NRD or the Gemma diets were significantly lower than the FCR of fish fed the Progression diet. SGR values were 6.6%, 6.3%?and 5.6%/day, and FCR values were 1.03, 1.11, and 1.31 for fish fed the NRD, Gemma, and Progression diets, respectively. RGR values were 1,439%, 1,212%, and 895%, and DWG values were 0.33 g, 0.27 g, and 0.20 g/day for scup fed the NRD, Gemma, and Progression diets, respectively.     

The effects of feeding frequency on growth of juvenile Atlantic halibut, Hippoglossus hippoglossus L.

Four experiments were conducted to investigate the effects of feeding frequency on growth of juvenile Atlantic halibut, Hippoglossus hippoglossus L. Fish (22–75 g) fed three (3 ×) or five times per day (5 × day^?1) under constant light and temperature (13±1°C) consumed significantly more feed than fish fed 1 × day^?1 but by the end of the experiment only fish fed 5 × day^?1 were heavier and had greater specific growth rates (SGR). Under simulated winter conditions (9L:15D, 5±1°C), halibut (～300 g) fed every other day consumed more feed, had a greater SGR and final weight compared with fish fed every third day. Feed conversion ratios were not different among treatment groups in any of the experiments. These results suggest that growth rates may be improved by feeding juvenile halibut more than 1 × day^?1.     

Estimation of Arachidonic Acid Requirement for Improvement of Pre‐maturation Growth and Egg and Larval Quality in the Female Blue Gourami (Trichopodus trichopterus; Pallas, 1770): A Model for the Anabantidae Family

This study investigates the dietary arachidonic acid (ARA) requirement from juvenile to maturation stage in an anabantid model fish, the blue gourami, Trichopodus trichopterus. Specifically we determined the optimum dietary ARA content to maximize juvenile growth and subsequent sexual maturation and to improve the quality of their eggs and offspring. Five experimental diets containing 0.02, 0.53, 1.05, 1.60, and 2.12% ARA (of dry weight) were fed to juveniles over 5 mo. The results showed that whole‐body fatty acid profile of broodstock significantly changed in fish fed diets of different ARA content (ANOVA, P < 0.003). The highest contents of 18:2n‐6 and Σn‐6 were obtained in fish fed 0.53% ARA, and a decreasing trend was observed with elevated dietary ARA levels. Monthly specific growth rate (SGR) measurements revealed significant differences in the juvenile stage, but the SGR of broodstock was unaffected by dietary ARA. Protein and ash content of whole‐body broodstock showed no differences among groups, while lipid content decreased as ARA levels increased. Maximum volume of the oocyte was obtained in the 1.05% ARA group, while the yolk sac size increased as dietary ARA increased. The optimum growth and survival of the larvae produced by broodstock were recorded in the 2.12 and 1.6% ARA groups, respectively. It was concluded that despite the presumed ability of freshwater fish to synthesize and meet their highly unsaturated fatty acid requirements, dietary ARA higher than 1.05% had significant stimulatory effects on growth of juveniles but no obvious influence on the growth of matured fish. Also, higher ARA levels (1.6–2.12%) were found to improve the quality of eggs and offspring.     

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.     

Protein requirement of jundia fingerlings, Rhamdia quelen, at two dietary energy concentrations

A feeding trial was carried out where five protein concentrations [26%, 29%, 33%, 37%, and 41% crude protein (CP)] were fed to jundia fingerlings at two dietary energy concentrations [3200 and 3650 kcal metabolizable energy (ME)/kg diet] to establish the protein requirement for this species. Triplicate groups of 23 fish (average weight 1.52±0.34 g) were each stocked in 120-l aquaria and fed semipurified diets twice a day to apparent satiation. After 90 days, fish weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), energy retention (ER), apparent net protein utilization (ANPU), feed consumption (% body weight) and body composition (crude protein, fat, and ash) were affected by diet composition. Weight gain, SGR, FE, ANPU and ER increased (P<0.05) as the dietary protein concentration increased up to 33% and 37%, for fish fed diets containing 3650 and 3200 kcal, respectively. A significant interaction between dietary protein and energy was observed for WG, SGR, and PER. Feed consumption was not affected by dietary energy concentration, but decreased with increasing dietary protein concentration (P<0.05). Body fat decreased as dietary protein increased at both energy concentrations, but was higher in fish fed the 3650 kcal diet. The opposite was observed for body protein, ER, and ANPU (P<0.05). Our findings demonstrate that jundia presents dietary protein sparing effect when the energy concentration increases from 3200 to 3650 kcal/kg. Jundia protein requirement, determined by the broken line method, is between 32.6% and 37.3% CP, depending on dietary energy concentration.     

Optimization of Feeding Rate for Hatchery-Produced Juvenile Gilthead Sea Bream Sparus aurata

Abstract.— A 61-d growth trial (five 11-d feeding periods) was conducted to determine the effects of feeding rate on growth, feed utilization, morphology, and body composition of the gilthead sea bream Sparus aurata . Gilthead sea bream juveniles with an average initial body weight of 3 g were fed a commercial diet (51% crude protein, 11% crude fat) at rates of 0.5, 1.0, 1.5, 2.0, 2.5, or 3.0% of their body weight (BW) per day in two equal meals. Water temperature was approximately 21.4 C throughout the experiment. Each ration was administered to triplicate groups of 60 fish, with ration readjusted every 11 d. Growth rate was measured as specific growth rate (SGR). Survival rate and coefficient of variation did not differ significantly among the groups fed different rates. Body weight, condition factor, and hepatosomatic and viscerosomat-ic indices displayed significant increases with increasing feeding rate from 0.5 to 3.0% BW/d. Fish fed 0.5% BW/d had significantly higher moisture and ash and lower protein contents than those fed at higher rates. Moisture and protein contents were not significantly different for fish fed at the highest feeding rates (2.0, 2.5, and 3.0% BW/d). Lipid contents increased significantly with increasing feeding rate from 0.5 to 3.0% BW/d. The SGR showed a curvilinear significant increase when the feeding rate was increased from 0.5 to 3.0% BW/d. Feed efficiency (FE) increased significantly to a maximum value with increasing feeding rate from 0.5 to 2.0% BW/d and decreased significantly with increasing feeding rate from 2.5 to 3.0% BW/d. Based on the data obtained, feeding rates of 2.3% and 0.6% BW/d are recommended as optimum and maintenance rations, respectively.     

Sexual dimorphism of fast muscle fibre recruitment in farmed Atlantic halibut (Hippoglossus hippoglossus L.)

Commercially farmed Atlantic halibut (Hippoglossus hippoglossus) were reared at the Aga Marin's facility located on Dønna (Norway) under ambient environmental conditions in duplicate 15 × 15 × 8 m netpens (May 2004 to May 2005). Twenty fish were sampled five times over a twelve month production period during which time the average body weight increased from 1.26 to 2.08 kg (n = 100 fish). Body mass, fork length (L_F), and the number and size distributions of fast muscle fibres were determined in male and female fish. All males matured during the autumn whereas no maturation was observed in females. From the point of maturation females had superior growth performance to males and body mass and the total cross-sectional area of muscle were 1.4-fold (P < 0.05) and 1.3-fold higher (P < 0.01) respectively by May 2005. The total number of fast muscle fibres per trunk cross-section at 0.55 L_F was 24.5% higher in females (7.58 × 10⁵) than males (5.80 × 10⁵) prior to sexual maturation. In females, muscle fibre recruitment slowed with short days and low water temperatures (< 6.5 °C), but had increased to 1.01 × 10⁶ by May 2005 (P < 0.001). In contrast, there was no growth and no increase in muscle fibre number in males following the onset of maturation. The distribution of muscle fibre diameters prior to maturation in males was also significantly different between male and female fish matched for L_F. The results illustrate a sexual dimorphism of muscle fibre recruitment patterns in Atlantic halibut and highlight the adverse affects of sexual maturation in males on muscle growth.     

Effect of diets containing a purified soybean trypsin inhibitor on growth performance,digestive proteases and intestinal histology in juvenile sea bream (Sparus aurata L.)

Juvenile sea bream were fed on diets containing 0.0, 2.0 or 4.0 g kg^?1 of a soybean trypsin inhibitor (SBTI) for 30 days. The growth performance, total protease activity and intestinal histology were studied after 0, 15 and 30 days of dietary treatment. No significant differences were found in the weight gain, specific growth rate (SGR) and feed conversion rate in fish fed on inhibitor‐supplemented diets when compared with those fed on an inhibitor‐free diet. Only the SGR at day 15 decreased significantly with protease inhibitor inclusion, although this effect was not observed at day 30. In relation to proteolytic activity at day 15, the total protease activity in the distal intestine decreased in fish fed on inhibitor‐supplemented diets. Zymograms of these extracts showed that the SBTI reduced the intensity of some proteolytic fractions in the distal intestine. A noticeable reduction in the protease activity of the intestinal content in fish fed on the highest level of soybean inhibitor (4.0 g kg^?1) was also observed. However, at day 30, the inhibition effect on these active bands was not detected, and the total protease activity was similar to that in fish fed on an inhibitor‐free diet. Histological examination revealed no perceptible differences in the intestinal structure between any of the diet groups. In addition, all fish were maintained under experimentation for 10 more days and fed on an inhibitor‐free diet to determine whether the possible effects caused by the protease inhibitor could be reverted. The administration of SBTI‐supplemented diets did not affect sea bream growth performance or intestine histology after 30 days, and only a decrease in the total alkaline protease activity was found at day 15.     

Dietary utility of enzyme-treated fish meal for juvenile Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

ABSTRACT:   In order to develop an artificial diet, the dietary utility of enzyme-treated fish meal was investigated for juvenile Pacific bluefin tuna Thunnus orientalis (PBT). Diets containing each 63% of Chilean fish meal (FM), enzyme-treated Chilean fish meal (EC) and enzyme-treated Peruvian fish meal (EP), with 10% bonito oil and raw sand lance Ammodytes personatus (SL) were fed to juvenile tuna six times per day for one week. In a different trial, diets EC and SL were fed to tuna six times per day for 2 weeks. Only diet EC sustained similar growth or caused lower survival and higher feed efficiency, hepato- and enterosomatic indices and final carcass lipid content as compared to those of SL. Diets FM and EP led to lower specific growth rate (SGR) but similar feed efficiency, survival and hepatosomatic index, yet higher enterosomatic index. Moreover, PBT fed diet EC for 2 weeks led to similar growth performance but higher final carcass and hepatic lipid contents, and plasma cholesterol and phospholipid levels than those fed SL. Carcass fatty acid composition of diet EC group had lower 20:5  n -3 and 22:6  n -3 levels than the SL group. These results revealed that EC, as a suitable dietary protein source, could sustain growth of PBT, while dietary bonito oil led to higher carcass lipid but lower accumulation of n -3 highly unsaturated fatty acids.     

Effect of Feeding Frequency on Sex-Reversal and on Growth on Nile Tilipia,Oreochromis niloticus

Methyltestosterone-treated feed was fed at four different feeding frequencies to Oreochromis niloticus fry held in hapas in order to evaluate the effect on sex reversal and on growth. Sex reversal rates greater than 97% were obtained for feeding rates ranging from 2 times/day, 5 days/week, to 4 times/day, 7 days/week. Greatest growth and lowest feed conversion occured when the fry were fed 4 times/day vs. 2 times/day. Fish were graded to sizes &#le; 15 mm and > 15 mm at the end of the 30-day treatment period and later sexed. There was no difference in the percent males between small or large fish.     

Periodic changes in the growth performance and biochemical composition of juvenile red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis> fed non-heated and heated squid and krill meal-based diets

In finfish aquaculture, fish meal is heated during the manufacturing process, which affects the digestibility and protein absorption by fish. However, manufactured fishmeal that is not heated does not undergo thermal denaturation. Few studies have investigated the effects of non-heated animal protein sources on the growth performance of fish. We investigated the effects of heated and non-heated squid and krill meal as diets for red sea bream. Five test diets were formulated to contain heated squid meal, non-heated squid meal, heated krill meal, non-heated krill meal, and fish meal as a control. Fifty fish (initial mean weight?=?3.5 g) were distributed in ten 100-l experimental tanks. Fish were fed one of the five diets 3 times daily until satiation for 5 weeks. Regarding growth performance, fish fed the krill meal diet exhibited better growth than those fed squid meal during the first week of the rearing period. However, the squid meal diet group showed better performance than the krill meal diet group during the third week. Moreover, differences in body weight among treatments were greater during the fifth week. Better weight gain and thermal growth coefficient were recorded in the non-heated diet groups than in the heated diet groups. Higher feed intake was observed in the non-heated diet groups than in the heated diet groups. These results suggest higher performance of non-heated squid and krill meal as the protein source of the red sea bream diet. Further, the suitability of the diet type (e.g., squid and krill) might depend on the feeding period and/or developmental stage of fish.