Influence of reward level on vertical distribution and growthof rainbow trout Oncorhynchus mykiss fed on demand with self-feeders

ABSTRACT:   The influence of reward level on vertical distribution and growthwas examined in rainbow trout fed on demand with self-feeders. Groupsof 15 trout with initial body weight of 140 g were maintainedat 14°C and feed access was restricted to a 12-h photophase.The trout received three reward levels with triplicates: 0.051 (low),0.089 (medium) and 0.267 g/kg fish/triggeractuation (high). Vertical distribution in the higher reward groupswas generally more even than that in the lower-reward groups, butthe behavioral characteristics of some individuals in a group couldplay an important role in determining vertical distribution. Moreover,no fish including the individuals responsible for trigger actuation,occupied the vicinity of a trigger. The small groups of 15 troutreceiving the medium-reward level obtained as much feed and grewas fast as the high-reward groups, but this was not the case forthe low-reward groups.     

Changes in demand feeding behaviour in Arctic charr, Salvelinus alpinus L., caused by differences in dietary energy content and reward level

The objective of this study was to determine whether Arctic charr, Salvelinus alpinus L., are able to adjust their demand feeding behaviour in accordance to differences in dietary energy content (experiment 1) and reward level (amount of food received in response to one trigger actuation) (experiment 2). Fish (initial size 215 g in experiment 1 and 88 g in experiment 2) were reared in 0.8-m³ indoor tanks at commercial stocking densities and fed using demand feeders for 57 and 180 days, respectively. Demand feeding activity did not differ significantly between groups of charr fed diets with a low (19.8 MJ kg^-1) gross energy content and those given high-energy (22.0 MJ kg^-1) feed. As a result, fish offered the high-energy diets grew significantly faster. The results show that charr held under culture conditions are unable to adjust their demand feeding activity based on the energy content of the food. On the contrary, Arctic charr are able to adjust their demand feeding activity to either low (0.33 g), medium (0.87 g) or high (1.52 g) rewards, and thereby, regulate their food supply to fit their needs. However, it took about 90 days before charr in the low-reward treatment released a daily food ration as high as that released in the high-reward groups. Consequently, there was a significant positive relationship between the size of the reward and final weights. To avoid any depression of initial growth rates, the optimal size of the reward should be 0.1 g per kg fish and trigger actuation.     

Self-feeding activity of a pleuronectiform fish, the barfin flounder

The self-feeding activity of the barfin flounder (Verasper moseri) was examined under natural photoperiod and temperature. The experiment, carried out over 12 weeks from September to December, involved tagged fish (mean body weight: 371 g) reared in three 1000-l tanks (3 or 5 fish per tank) with a self-feeder device. The sensor comprised a switch and trigger string with a bead. Self-feeding activity was recorded in all tanks from day 1. The fish fed mostly at night. Strong positive correlations were observed between the number of daily feeder activations and water temperature/photoperiod, and all fish grew during the experiment. These results demonstrate that barfin flounder can operate self-feeding systems and it is suggested that self-feeding activity is influenced by photoperiod and water temperature.     

Feeding behaviour, energy expenditure and growth of rainbow trout in relation to stocking density and food accessibility

The effect of stocking density on feed intake, feed utilization and feeding behaviour was studied in groups of rainbow trout submitted to different levels of food accessibility. In the first experiment, 18 groups of 100, 300 or 500 fish (initial individual weight 26 ± 0.5 g) were held in 1 m³ tanks where they were fed: in excess using belt feeders; or by means of self‐feeders with a fixed reward level (4 g per trigger actuation); or a reward level proportional to fish density (2 g/100 fish/trigger actuation). Final biomass after 125 days was c. 25, 70 and 100 kg/m³ in groups of 100, 300 and 500 fish respectively. Growth and feed intake was affected by fish density, feeding technique and reward level. However, feed efficiency, body composition, as well as nutrient retention and loss were unaffected by the treatment. In the self‐fed groups, daily pattern of feeding activity was affected by fish density when the reward level was fixed but not when the reward level was proportional to fish density. In a second experiment, groups of 100 or 500 fish (same initial individual weight) had access to one or three self‐feeders. Access to multiple self‐feeders had no positive effect on any of the studied parameters. The fish used only one of the three feeders at a time, and the three feeders where not used equally. We conclude that feed intake but not feed utilization was impaired by increased density, indicating that density in itself is not stressful to the fish. Food accessibility is the main factor responsible for the observed density – related decrease in growth.     

A simple way of avoiding feed wastage in European seabass,Dicentrarchus labrax,under self-feeding conditions

Self-feeding systems allow fish to freely express feeding activity. A simple rod at the water surface can act as a trigger and provide fish with a way of obtaining pellets from a feeder. Such a rod presented to experienced European seabass, Dicentrarchus labrax, may lead to feed wastage, probably as a result of unintentional fish contacts with the trigger. Trigger protection screens have been designed to prevent fish contacting the trigger by chance, and the efficacy of such screens was tested. Nocturnal and diurnal feed delivery and feed wasted were compared under conditions where the rod was unprotected or protected by semi-cylindrical or cylindrical screens. Tests were conducted using an unrestricted self-feeding regime (reward: 0.2 g pellet per kg of body weight and per fish contact) in juvenile seabass (57 g body weight) fed for 28 days at 21.3 °C. Fish were subjected to a 4-h L:20-h D (light:dark) photoperiod. The daily feed demand pattern and the nocturnal and diurnal feed wastage were recorded. Fish activated the trigger predominantly at night, except in the case of one group exposed to a trigger protected by a semi-cylindrical screen. In the latter, triggering activity was progressively distributed throughout the light:dark cycle. The cylindrical screens markedly reduced feed wastage and seabass were able to locate and activate the trigger (even in total darkness) to obtain a reward.     

Feeding habits of skipjack tuna Katsuwonus pelamis and other tuna Thunnus spp. juveniles in the tropical western Pacific

ABSTRACT: The feeding habits of skipjack tuna Katsuwonus pelamis juveniles (8.5–66.8 mm standard length) were examined, collected from the tropical western Pacific in October to December 1994, and their habits were compared with those of the other tuna Thunnus spp. juveniles (9.8–55.3 mm standard length). The indices, frequency of occurrence of each food item in the total number of stomachs examined (% F ), percentage of number of each food item to the total number of all food items identified (% N ), percentage of wet weight of each food item to the total wet weight of all food items identified (% W ), and relative importance of each food item ( IRI ) were estimated in the north equatorial current (NEC) and the north equatorial countercurrent (NECC) areas. The most dominant prey item of skipjack juveniles in the two areas was fish larvae. Other major prey items in the NEC area were Euphausiacea, Amphipoda, and Copepoda; whereas those in the NECC area were Copepoda, Cephalopoda, Euphausiacea, and Amphipoda. In the other tuna juveniles, the IRI of fish larvae in the two areas was remarkably high. Other prey, Euphausiacea and Cephalopoda in the NEC area only and Cephalopoda in the NECC area, were also found. These results indicate that the skipjack juvenile is primarily a piscivorous feeder although they also depend on various other prey organisms, whereas the other tuna juveniles are stronger piscivorous feeders.     

Does timing of daily feeding affect growth rates of juvenile three‐spined sticklebacks,Gasterosteus aculeatus L?

Abstract – To assess the consequences of unpredictability in the availability of food, this study measured the effect of timing of the daily feeding on food consumption and growth rates of juvenile Gasterosteus aculeatus. The experiment lasted 21 days at 14 °C and a photoperiod of 10 hours of light and 14 hours of dark. Fish were housed individually and allocated at random to three treatments. The mean initial weight of fish was 0.402 g. Group 1 were fed live enchytraeid worms for 2 h after lights came on ("morning"), group 2 was offered food for 2 h randomly at any time of the day ("random") during the light period and group 3 received food for 2 h before the lights went off ("evening"). There was no significant effect of timing of feeding on mean daily food consumption, which was 0.052 g day⁻¹. Daily consumption on the random schedule was more irregular than on the two fixed schedules. Timing of feeding had no significant effect on mean specific growth rate (G) (2.42% day⁻¹), gross growth efficiency (23.3%), white muscle RNA:DNA ratio (5.6), carcase lipid content (31.7% dry wt) and carcase dry matter content (27.4% wet wt). Thus, a lack of predictability in the availability of food during the light period of the day did not impose a detectable cost on the growth performance of the stickleback.     

A test of the individual feeding activity and food size preference in rainbow trout using demand feeders

Feeding activity and food size preferences were investigated in three groups of rainbow trout with initial weights ranging from 200 to 1000 g. Fish were given the option of releasing food from either of two demand feeding devices that contained either 6 mm or 9 mm food pellets. Individual biting activity (to activate release of food) was continuously monitored using specially designed passive integrated transponders (PIT-tags). In each of the groups, biting activity was strongly influenced by three individuals, which accounted for 70–85% of the total. Thus, high bite activity by few individuals indicates the development of social dominance hierarchies. There was no statistically significant correlation between number of bites and growth rate, indicating that the fish that operated the demand feeders did not gain any growth advantage. Trout that dominated the actuation of the feeders were found among both medium- and large-sized fish. There was no evidence of active food size selection, and the fish that most frequently operated the feeders defended one area of the tank rather than preferring the trigger that would have delivered food of the optimal size.     

Sur le sevrage et l'evolution des performances biologiques d'alevins de daurades,Sparus auratus,provenant d'elevage extensif,apres remplacement des nourrisseurs en continu par des distributeurs libre service

Extensively reared 0.13 g Sparus auratus sea bream fry were placed under intensive conditions (one individual per litre) and progressively weaned with dry pellets by two successive methods: prescribed feeding, and self-feeding. Results show that biological and ecological data on fry productivity are strongly dependent on feeding strategy. During the first period when pellets were supplied with a 9 h/day continuous feeder, production data are technically and economically correct but biologically poor (food conversion ratio 5 to 7; chronic mortality of 0.77% per day; disastrous hydric conversion ratio of 2415 m³/kg production). On the other hand, during the second period when the fry were self-feeding and free to regulate their feeding pattern, biological data become very good (food conversion ratio 1.95; mortality less than 0.03% day; hydric conversion ratio of 249 m³/kg production).The two techniques are discussed and compared in their ecological, metabolic and physiological aspects.     

Food distribution equipment for individually-housed juvenile lobsters (Homarus spp.)

The construction and operation of two simple mechanical feeders, one for use with dry pellets, the other with a suspension of mysid shrimps in seawater, are described. Both feeders were designed to facilitate the feeding of large numbers of individually-housed crustaceans held in laboratory and nursery water table systems.

The dry feeder delivered between 2 and 6 pellets to 91% of the individual compartments with less than 2% receiving no food. The wet feeder delivered between 3 and 9 mysids to 73% of the compartments with 2·1% receiving no food. The distribution of empty compartments was random so that it was unlikely that the same animals would go without food after two successive feeds.     

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.     

Influence of dietary fat and carbohydrate levels on growth and body composition of rainbow trout Oncorhynchus mykiss under self-feeding conditions

SUMMARY: An 8-week feeding experiment was conducted to examine the influence of fat and carbohydrate levels in a 40% protein level diet on growth and body composition of rainbow trout Oncorhynchus mykiss under self-feeding conditions. Five fish meal-based diets were prepared to include gelatinized potato starch at four levels (9, 18, 27, and 36%) and dextrin (34%). Dietary fat levels were isoenergetically reduced from 18 to 7% by the digestible carbohydrates. Each diet was fed to four replicate groups (28 g/fish, 20–23 fish/group) using self-feeders. Specific growth rate, percentage weight gain and percentage protein retention did not differ between the treatments. Feed efficiency and protein efficiency ratios were higher in the 18% starch (s18) and s27 diet groups, and decreased in higher fat or carbohydrate diet groups. Although gross energy intake (kJ/kg BW per day) decreased as the starch level increased, levels of digestible energy intake did not differ between the treatments. Fat levels in the carcass, viscera and liver decreased as dietary carbohydrate level increased. These results suggest that a 40% protein diet with either 15% fat and 18% starch or 11% fat and 27% starch is appropriate for juvenile rainbow trout under self-feeding conditions.     

Feeding,growth, and blood chemistry of the tambaqui (Colossoma macropomum) held under self-feeding and time-restricted automatic feeding conditions

This work evaluated the effects of food frequencies and self-feeding on the behavior, performance, and blood biochemistry of Colossoma macropomum. Juveniles weighing 3.63?±?0.05 g were distributed in 27 aquariums (40 L), with six fish per aquarium, to evaluate nine treatments in three replications in a 12L:12D photoperiod. The treatments were 24-h self-feeding (SF); daytime self-feeding at will (SFD); nighttime self-feeding at will (SFN); and feeding at fixed frequencies of two (2D), four (4D), and six times (6D) daytime and twice (2 N), four (4 N), and six times (6 N) nightly. The treatments were offered in automatic feeders, with fixed frequencies programmed. Extruded commercial feed, with 46% protein, was used. The experimental period was 40 days. In the SF treatment, the animals exhibited 95.7% nocturnal and 4.3% diurnal feeding activity (p?<?0.05). In the treatment SFD and SFN, the animals showed feeding activity throughout the day and night. Final weight, weight gain, and total feed intake were higher for animals at fixed daytime and nighttime frequencies (p?<?0.05). Feed conversion was better for animals in SF, SFD, 4D, SFN, and 4 N (0.89, 0.76, 0.91, 0.85, and 0.88, respectively) (p?<?0.05). Cholesterol and high-density lipoproteins were lower for fish in SF, SFN, 2 N, 4 N, and 6 N (p?<?0.05). SF treatment animals had lower triglyceride content, 154.20 mg dL^?1 (p?<?0.05). Colossoma macropomum has nocturnal food preferences, however, with remarkable plasticity. Juveniles of this species fed four times during the day or night show good performance. Dietary patterns influenced the blood metabolic indicators of this species and the periods studied.

     

Self-feeding behavior of yellowtail, Seriola quinqueradiata, in net cages: diel and seasonal patterns and influences of environmental factors

The self-feeding pattern of yellowtail, Seriola quinqueradiata, maintained in floating net cages was examined throughout a year, and the influence of seasonal changes of the photoperiod and water temperature on the feeding pattern was investigated. Two groups of 50 yellowtail (initial mean body weight about 50 and 80 g, respectively) were kept in two experimental net cages (2×3×4 m deep), with a self-feeding device installed on each. It was possible to maintain yellowtail in net cages using a self-feeder throughout almost a year. The number of daily food demands was greatly affected by the seasonal changes in water temperature. Yellowtail showed high self-feeding activity, above 18 °C; depressing water temperatures did not influence the activity when the water temperature was over 18 °C. However, the activity decreased when the water temperature fell below 18 °C. The feeding pattern in a 24-h period was greatly affected by the temporal changes in light intensity. Annual observations revealed that yellowtail showed generally crepuscular plus nocturnal feeding behavior and had two peaks of feeding activity a day. These peaks appeared at dawn and dusk; moreover, a clear association between the most active time of self-feeding and the period of the greatest change in light intensity was observed. The results suggest that a change in light intensity might stimulate the appetite of yellowtail or that there is a light level at which yellowtail prefer to eat.     

Resource partitioning between lake-dwelling Atlantic salmon (Salmo salar L.) parr, brown trout (Salmo trutta L.) and Arctic charr (Salvelinus alpinus (L.))

Abstract – Resource partitioning between Atlantic salmon parr, brown trout and Arctic charr was studied throughout the ice-free season in a north Norwegian lake. Juvenile salmon and trout (≤160 mm) utilized the littoral zone and juvenile charr the profundal, while adult trout and charr (>160 mm) were found in both. Juvenile salmon and trout had a similar diet, although trichopteran larvae were more important for the trout and chironomid pupae and three-spined sticklebacks for the salmon parr. Small salmon and trout parr (≤120 mm) had a higher diet overlap than larger parr (121–160 mm). The feeding habits of adult trout were similar to that of juvenile trout, but the former took larger prey items. At the population level, both salmon and trout were generalistic feeders with a broad diet, but at the individual level, both species had specialized on a single or a few prey categories. Juvenile charr were segregated from salmon and trout in both habitat and food utilization; they had a narrow diet consisting of chironomids and zooplankton, possibly reflecting their confinement to the profundal habitat which have a low diversity of potential prey. Larger charr also took zoobenthos and sticklebacks in the littoral zone. ^Note     

Response changes with growth in the gustatory receptors of young yellowtails (Seriola quinqueradiata)

SUMMARY: Laboratory-hatched juvenile yellowtails (mean fork length, 9.3 cm) were reared for 2 months in two groups on different kinds of food, mysid and squid in one group and fish in the other, and the gustatory neural responses to seven chemicals (adenosine-5'-monophosphate, alanine, arginine, betaine, proline, tryptophan, and valine) were recorded in fish before and after the 2-month rearing period. Large variances in the responses to some chemicals were noticed in the juveniles before the rearing experiment. Mann–Whitney U -tests on the neural responses indicated significant changes in the magnitude of the responses to valine and some other chemicals relative to that for proline or tryptophan between the pre- and the two post-rearing groups. No significant differences in the response magnitude for the seven chemicals were observed for the two post-rearing groups suggesting that the response changes during the 2-month rearing might have been intrinsic and not due to specific food items in the diet. The dose–response relationship for some chemicals was also examined in the juveniles before and after the 2-month rearing. A slight lowering of threshold was noticed for alanine and valine after the rearing. Data on the responses of wild yellowtails were in support of the changing responsiveness of gustatory receptors during development of juvenile yellowtails.     

Hybrid fish model (Pseudoplatystoma reticulatum♀ × Leiarius marmoratus♂) to study feeding behaviour: protein source self‐selection and demand‐feeding rhythms

We report feeding studies on hybrid fish (carnivorous × omnivorous) to determine the interactions between protein sources during diet selection trials. We also examined behavioural rhythms (feeding and locomotor activity) using a self‐feeding system mounted with a feeder connected to an infrared photocell. Twenty fish (28.20 ± 0.05 g) were distributed in four aquariums (50 L each). First, the system was tested to evaluate the adaptation of catfish (Pseudoplatystoma reticulatum × Leiarius marmoratus) to self‐feeding (step I). During this 28‐day period, feeding and locomotor activity rhythms were recorded. In the second step, to analyse protein self‐selection, a group of 20 fish (19.10 ± 0.05 g) was released in the aquaria. The hybrid catfish were given free access to diets (soya bean meal protein (SP) vs. bovine liver protein (BP)) through two self‐feeders. The same procedure was used for (SP) vs. fish meal protein (FP). The catfish learned to activate the feeders to demand a daily feed amount equivalent to 1.8% of their body weight. The fish performed most of their actions (89.0% feeding activity and 94.1 0% locomotor activity) in the night. The diet choice by the catfish became clearer with a significantly lower intake of BP (0.37 g per 100 g body weight, 24.6%) vs. SP (1.06 g per 100 g body weight, 75.4%) and SP (0.61 g per 100 g body weight, 38.9%) vs. FP (0.91 g per 100 g body weight, 61.1%). These findings should be considered when discussing feeding behaviour, nutritional targets and protein sources for future aquaculture feeds.     

Transitioning to a Pelleted Diet and Compensatory Growth of Pacific Goliath Grouper Epinephelus quinquefasciatus in Captivity

The objective of this study was to adapt juvenile Pacific goliath grouper to a diet of pelleted feed. Groupers were captured in nature, individually marked, and randomly assigned to two groups. One group was fed pieces of raw fish and the second group a pelleted feed. The experiment lasted 12 weeks, and adaptation to the pelleted feed was done gradually. Fish growth, weight gain, and specific growth rate (SGR) were estimated. The Student’s t-test, at the 0.01 level of significance, was used to compare SGR means. All the fish survived. The rate of growth for grouper fed pieces of raw fish was 1.6 g per day. Although the groupers fed the pellets lost weight at the beginning of the experiment, at the end their SGR was 5.5 grams per day. The average weight gain for juvenile grouper fed pellets was 14.6 ± 4.1 g per day.     

Further clarification of winter energy and protein requirements at the optimum feeding frequency for yellowtail

SUMMARY: This is another report from a series of studies aimed at determining the energy and protein requirements based on the optimum feeding frequency of yellowtail during the winter season. Experiments were conducted at Mie and Oita Prefectures, Japan, employing extruded pellets of known digestible energy (DE) and digestible protein (DP) values. Four groups of fish were fed at frequencies of five, three, two, and one time(s) per week. The most efficient feed performance was obtained for the feeding frequenecy of three times per week. The DE and DP requirements calculated based on the feeding rate at this frequency were 38.7 kcal and 2.8 g/kgBW per day (14.3–17.3°C) in Mie and 30.4 kcal and 2.2 g/kgBW per day (13.8–17.5°C) in Oita, respectively. The present results and the observations on the changes of the contents in digestive tracts tallied with our previous work, confirming that the optimum feeding frequency was three times per week.     

Effects of replacing fish oil with canola oil on the growth performance,fatty acid composition and metabolic enzyme activity of juvenile yellowtail Seriola quinqueradiata (Temminck & Schlegel, 1845)

In this study, fish oil (FO) was replaced with canola oil (CO) in juvenile yellowtail diets to establish the optimal replacement levels that ensure adequate feed quality for aquaculture. Juvenile yellowtails (initial body weight: 104.7 g) were fed one of four diets for 10 weeks: 100% FO (FO group) or FO replacement with 25%, 50% or 100% CO (CO25, CO50 and CO100 groups respectively). Body weight, specific growth rate and feed efficiency were significantly affected by the replacement of FO with CO. The final body weight of the CO100 group was significantly lower than that of the FO (control) and CO50 groups. Furthermore, the CO50 group showed significantly higher feed efficiency than the FO group during the first 4 weeks (long photoperiod and high water temperature conditions). Increasing dietary CO increased serum glucose and triglyceride concentrations in a dose‐dependent manner. Regarding the proximate composition of fillet and liver, only crude protein in fillet was affected by the replacement of FO with CO. Fatty acid compositions of fillet and liver were correlated to the amount of CO in each diet. The activities of the metabolic enzymes phosphofructokinase and alanine aminotransferase were lowest in the CO25 and CO50 groups respectively. Thus, FO replacement with CO affected growth performance, serum components, fatty acid composition and the activity of metabolic enzymes. Overall, results obtained in the present study suggest that partial replacement (50%) of FO with CO is effective and might increase juvenile yellowtail growth under long photoperiod and/or high water temperature conditions.