Evaluation of mixed feeding schedules with respect to compensatory growth and body composition in African catfish Clarias gariepinus

An 8‐week feeding trial was conducted in a recycling water system at 28 ± 1 °C to investigate compensatory growth and body composition in African catfish Clarias gariepinus (13.05 ± 0.05 g). A fishmeal‐based diet containing 350 g kg^?1 protein and 17.5 kJ g^?1 gross energy was fed to triplicate groups of 20 fish (per 30‐L tank). Fish were fed the diet either to satiation or feed restricted in six feeding schedules as satiation 56 days; restricted 28 days + satiation 28 days; restricted 14 days + satiation 14 days; restricted 7 days +satiation 7 days; restricted 3 days + satiation 4 days; and restricted 2 days + satiation 2 days. The restricted regime was achieved by offering fish 1% (maintenance ration) of their body weight per day adjusted after fortnightly weighing. African catfish showed partial compensatory growth under alternating periods of feed restriction and satiation feeding with significantly different values (P < 0.05) from fish fed in satiation throughout. However, significantly indifferent (P > 0.05) values of feed, protein, lipid and energy utilization were found under alternating periods of feed restriction and satiation feeding. Significantly higher (P < 0.05) feed intake was observed in treatment with satiation throughout than those in other treatments. All the feeding schedules showed no significant differences (P > 0.05) on body composition, organ indices, eviscerated carcass composition, viscera lipid and liver lipid. These studies reveals that C. gariepinus showed partial compensatory growth responses at alternating periods of restricted and satiation feeding.     

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.     

Comparison of the swimming performance of farmed and wild gilthead sea bream, Sparus aurata

Farmed gilthead sea bream, Sparus aurata, frequently escape from the sea cages and interact with wild populations. The impact of these interactions on the wild populations will depend, in part, on differences in performance of the bream. This study compared the swimming performance of the wild and farmed fish in a current channel. The absolute critical swimming speed (U_crit) increased with increasing size while the relative U_crit decreased. Even at the same length there were noticeable performance differences between the individuals. The wild sea bream have significantly higher (P<0.05) absolute U_crit performance (0.86±0.01 m s⁻¹) than the farmed fish (0.79±0.01 m s⁻¹) and significantly higher (P<0.05) relative U_crit performance (4.52±0.05 BL s⁻¹) than the farmed fish (4.21±0.05 BL s⁻¹). The present study suggests that cultured sea bream may not have the ability to compete with wild sea bream in native seawaters.     

Influence of pond fertilization and feeding rate on growth performance, economic returns and water quality in a small-scale cage-cum-pond integrated system for production of Nile tilapia (Oreochromis niloticus L.)

The effects of pond fertilization and feeding rate on growth, economic returns and water quality were investigated to develop a low‐cost cage‐cum‐pond integrated system for production of Oreochromis niloticus (L.). Hand‐sexed male fingerlings averaging 19±0.39 and 32±0.69 g were stocked in cages and open ponds at 150 fish cage^?1 and 2 fish m^?2 respectively. Fish were cultured for 114 days in five triplicate treatments. Cages were installed into ponds and caged fish were fed a 24% protein diet at 3% (T1) and 6% (T2) body weight day^?1 (BWD) without pond fertilization, and 6% BWD with pond fertilization (T3). The open water in the fourth treatment (T4) was not stocked but contained caged fish, which were fed 6% BWD for the first 57 days followed by 3% BWD for the remaining period. Ponds in the control (T5) had no cages and were neither fertilized nor open‐pond fish fed. Feeding rate and pond fertilization significantly (P<0.05) affected fish growth, profitability and water quality among treatments. Fish growth, feed utilization, fish yield, water quality and profits were significantly (P<0.05) better in T3 than the other treatments. It was concluded that fish production and economic returns were optimized at 6% BWD in fertilized ponds.     

Development of a feeding strategy for silver perch, Bidyanus bidyanus (Mitchell), based on restricted rations

To develop a feeding strategy for the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell), a series of eight experiments was done in 1 m³ cages in an aerated, earthen pond to determine the effects of feeding rate (% body weight) and feeding frequency (no. of feeds day^?1) on the growth and feed conversion ratio (FCR) of fingerlings and larger fish under ambient water temperatures over the range 13.8–30.6°C. Fish were fed extruded pellets of a silver perch diet containing 34% digestible protein and 14 MJ kg^?1 digestible energy. Commercial silver perch farmers were consulted about feeding practices for large fish (>500 g) and at water temperatures below 12°C, and winter feeding practices for other warmwater species were used to complete the strategy. In the feeding experiments, growth and FCR increased with increasing feeding rates to a level above which only FCR increased. Optimal feeding rates and frequencies were those which resulted in maximal growth, while minimizing effort (feeding frequency) and FCR. The highest feeding frequency required for maximal growth, including that of small fingerlings was twice (2 ×) daily, and the optimal feeding rates varied with water temperature and size of fish. The optimal daily regimes were: small fingerlings (initial mean weight, 2.0 g) 7.5% 2 × at a mean temperature of 23.3°C; fingerlings (14.9–27.7 g) 7.5% 2 × at 27.1°C, 5.0% 2 × at 23.7°C and 2.0% 1 × at 16.8°C; and large silver perch (162.5–510.6 g) 0.5% 1 × daily or 1.0% on alternate days at 15.6°C, 1.0% 1 × at 17.3°C, 3.0% 2 × at 24.1°C and 2.0% 2 × at 27.9°C. It is suggested that regimes of 0.5% 1 × daily for fingerlings (<50 g) and 0.5% 1 × on alternate days for larger fish are used at temperatures of 9–12°C, and 0.5% 3 days week^?1 and 0.5% 1 day week^?1 for fingerlings and larger fish, respectively, at 6–9°C. Feed inputs should not exceed 150 kg ha^?1 day^?1 in ponds less than 0.3 ha and 100 kg ha^?1 day^?1 in larger ponds. Our research has established a feeding strategy for silver perch based on restricted rations.     

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.     

Relationship Between Dietary Protein Source and Feeding Frequency During Feeding Nile Tilapia,Oreochromis niloticus (L.) Cultured in Concrete Tanks

ABSTRACT

A 24-week feeding trial was conducted in concrete tanks with Nile tilapia, Oreochromis niloticus (L.) with an average initial weight and length of 50.87 ± 6.03 g and 14.4 ± 0.45 cm, respectively, to examine the effect of two protein sources and two feeding frequencies on growth performance, production traits, and body composition. Twelve 4 m³ concrete tanks (2 × 2 × 1.25 m, long, width, and height) were each stocked with 100 fish and fed diets containing either fish meal protein or soybean meal protein at two feeding frequency of two times daily or four times daily (2 × 2 × 3 factorial experiment). The results revealed that there was no significant effect of dietary protein sources on growth rate, whereas there was a significant increase in growth rate with increasing feeding frequency (P < 0.05). The same trend was also observed for mean body weight (g), production rate (kg/m3), specific growth rate (SGR % day^?1). The best final mean body weight (g), specific growth rate (SGR % day^?1), and production rate (kg/m3) were recorded in groups of fish fed with feeding frequency four times daily. Whole fish moisture, protein, fat, and ash contents were significantly influenced (P ≤ 0.05) by protein sources and feeding frequency, except protein not influenced with feeding frequency. Energy was significantly (P < 0.05) influenced by feeding frequency, but not by dietary protein sources. Economic evaluation indicated that soybean meal (Diet B) at four times feeding daily was the most cost-effective and affordable feed strategy for farmers. We conclude that a soybean diet fed four times daily is recommended for adult Nile tilapia reared in concrete tanks.     

Optimum feeding rates in juvenile olive flounder,Paralichthys olivaceus,at the optimum rearing temperature

Two feeding trials were carried out to determine the optimum feeding rates in juvenile olive flounder, Paralichthys olivaceus, at the optimum rearing temperature. Fish averaging 5.0 ± 0.11 g (mean ± SD) in experiment 1 and 20.2 ± 0.54 g (mean ± SD) in experiment 2 were fed a commercial diet at the feeding rates of 0%, 3.0%, 4.0%, 4.25%, 4.5% and 4.75% body weight (BW) day^?1 and satiation (5.52% BW day^?1) in experiment 1 and 0%, 1.0%, 2.0%, 3.0% and 3.5% BW day^?1 and satiation (4.12% BW day^?1) in experiment 2 at 20 ± 1 °C. Both feeding trials lasted for 2 weeks. Results from experiment 1 indicated that weight gain (WG) and specific growth rate (SGR) of fish fed to satiation were significantly higher than those of fish fed at other feeding rates while feed efficiency (FE) and protein efficiency ratio (PER) of fish fed at 4.25% BW day^?1 were significantly higher than those of fish fed to satiation and fish fed at 3.0% BW day^?1 (P < 0.05). In experiment 2 WG, SGR and PER leveled out after the feeding rate of 3.5% BW day^?1 whereas FE reached a plateau at 3.0% BW day^?1. anova of FE indicated that the optimum feeding rates in 5.0 and 20 g juvenile olive flounder could be 4.25% and 3.0% BW day^?1, respectively. Broken line analysis of WG suggested the optimum feeding rates of 5.17% and 3.47% BW day^?1 in 5.0 and 20 g fish, respectively. Therefore, these results indicated that the optimum feeding rates could be >4.25 but <5.17% BW day^?1 for 5.0 g, and it could be >3.0 but <3.47% BW day^?1 for 20 g size of juvenile olive flounder at the optimum rearing temperature.     

The effect of light intensity on first feeding of the spotted sand bass Paralabrax maculatofasciatus (Steindachner) larvae

The effects of light intensity on feeding incidence and prey consumption at first feeding of spotted sand bass larvae (Paralabrax maculatofasciatus Steindachner), using four light intensity treatments (0, 100, 400, and 700 lx) were evaluated. Specimens were fed the rotifer Brachionus plicatilis at a density of 3 rotifers mL^?1. One hour after the addition of prey, 30±3 (mean±SEM) larvae were sampled from each treatment aquarium. Feeding incidence was evaluated as the percentage of larvae with prey in the digestive tract. Feeding intensity was measured as the number of prey in the digestive tract of the larvae. Histological analysis was carried out to describe the eye structure at the time of first feeding. Larvae fed in darkness (0 lx) had a significantly lower (P<0.05) feeding incidence (1.2±2.2%) and intensity (0.4±0.7 rotifers larvae^?1) than those larvae fed at 100 (28±11%, 1.8±0.2 rotifers larvae^?1), 400 (48±10%, 2.4±0.3 rotifers larvae^?1), and 700 lx (52±4%, 2.4±0.1 rotifers larvae^?1). Feeding incidence of the spotted sand bass larvae increased with light intensity while the feeding intensity showed no significant difference (P>0.05) between light treatments. Histological analysis of the eye structure showed that first feeding larvae had well‐formed lens along with a retina composed of pure single cones as photoreceptors.     

Enhancement of Monosex Hybrid Red Tilapia,Oreochromis mossambicus × O. niloticusProduction in Portable Canvas Tanks Through Mixed-Feeding Strategies

Abstract

The viability of mixed-feeding schedules utilizing low-and high-protein diets for the production of monosex hybrid red tilapia, Oreochromis mossambicus × O. niloticuswas evaluated. Male red tilapia juveniles (mean initial weight 16.8±0.08 g) stocked at a rate of 159 fish/m³ in canvas tanks (3.05m × 0.92m × 1.22m) were grown under five different feeding schedules for 24 weeks. Two schedules, using low (25%, A) and high (35%, B) dietary protein were designated as control. Three mixed-feeding schedules tested were: the feeding of 1 day of low protein diet followed by 3 days of high-protein diet (1A/3B); 2 days of low-protein diet followed by 3 days of high-protein diet (2A/3B); and 3 days of low-protein diet followed by 3 days of high-protein diet (3A/ 3B). Results showed that growth performance parameters, such as specific growth rate (% SGR), percent gain, and weight gain were significantly higher (P < 0.05) for fish maintained on the feeding schedule of 3A/3B. Similarly, the feed conversion ratio, protein efficiency ratio, and protein retention values were also significantly better for fish grown under this schedule. In terms of production, the 3A/3B feeding schedule also resulted in the highest total yield (kg/m³) and yield above 250 g. The 3A/3B feeding schedule resulted in a 10.1% protein saving relative to Diet B. These results suggest that a 3A/3B feeding schedule be adopted for the best biological and economical performance of red tilapia.     

Production performance of sutchi catfish Pangasianodon hypophthalmus S. in restricted feeding regime: effects on gut,liver and meat quality

The experiment was carried out to evaluate the production performance of sutchi catfish, Pangasianodon hypophthalmus in restricted feeding regimes and their effects on gut and liver indices and body composition. Four feeding regimes were evaluated: fed to satiation twice per day (treatment daily feeding); 1‐day food deprivation and 1‐day feeding (treatment 1D‐1F), 2‐day deprivation and 2‐day feeding (treatment 2D‐2F) and 5‐day deprivation and 5‐day feeding (treatment 5D‐5F). Fingerlings (mean weight 37 ± 3 g, mean total length 18 ± 2 cm) were stocked in replicated earthen ponds at a density of 25 000 ha^?1 and cultured for 18 weeks during which commercial diet (33% crude protein) were delivered to apparent satiation on the feeding day according to the treatment. Results showed that the daily feeding and 1D‐1F treatments resulted in similar individual weight gain (515–536 g) and net fish production (10 954–11 387 kg ha^?1) as compared with treatment 2D‐2F (weight gain 309 g; net production 6700 kg ha^?1) or treatment 5D‐5F (weight gain 251 g; net production 5651 kg ha^?1). While fish body protein levels were not affected by food deprivation, lipid contents were lowest in treatments 2D‐2F and 5D‐5F. The study concluded that sutchi catfish could be cultured in alternate‐day feeding regime without any negative effects on production and meat quality of fish resulting in a net profit of USD 2750 ha^?1 pond.     

Effect of feeding delay after self‐feeder activation on growth performance and feeding behaviour of red porgy (Pagrus pagrus L. 1758): application to submergible cages with surface hopper

Red porgies (Pagrus pagrus) of 20.6±1.5 g mean weight were reared in tanks under four delayed self‐feeding conditions (0=control, 7, 30 and 90 s) after rod activation. The time intervals were chosen to simulate the time taken for a commercial pelleted feed to transit the tube linking a surface‐mounted feed hopper and the depth at which a cage might be submerged. Daily feeding rate, growth, food conversion index and condition factor were quite similar but fish behaviour differed among conditions. Fish remained close to the feeding point in the first two treatments (0 and 7 s delay) but foraged more widely in the remaining treatments (30 and 90 s delay), only reconsolidating around the feeding point a few seconds before feed was released. Results are discussed in relation to learning capacity and adaptation of fish to feeding behaviour flexibility, in order to develop reliable self‐feeding systems suitable for submerged cages.     

Effect of feeding frequency on growth, survival and feed utilization in fingerlings of Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton) in outdoor rearing systems

Fingerling rearing of Indian major carps, Catla catla, Labeo rohita and Cirrhinus mrigala, were conducted in concrete tanks under a polyculture system at a density of 0.3 million fry ha^?1 to evaluate the effect of one, two or three feedings per day on growth, survival and feed utilization. Fry were fed with formulated supplementary diet at 10% of biomass per day during the first 15 days, followed by 8% in the next 15 days and 6% thereafter, for 60 days. Feeding of fish three times daily led to higher growth (103.9±8.5 mm/10.3±2.4 g) than those feeding twice (100.2±4.8 mm/9.9±1.5 g) or once (97.2±9.8 mm/9.4±2.1 g) daily, although the values were not significantly different (P>0.05). Survival rate ranging between 72.3% and 75.1% also did not vary significantly (P>0.05) among the treatments. However, higher feeding frequencies resulted in better feed utilization as evident from decreasing feed conversion ratio values. The present study suggested requirement of a higher feeding frequency for rohu compared with catla and mrigal.     

Effect of dietary protein levels and feeding rates on growth performance, production traits and body composition of Nile tilapia, Oreochromis niloticus (L.) cultured in concrete tanks

A 28‐week feeding trial was conducted in concrete tanks with Nile tilapia, Oreochromis niloticus (L.) with an average initial weight and length of 61.9±6.03 (g fish^?1) and 17.6±0.45 (cm fish^?1), respectively, to examine the effect of two protein levels and three feeding levels (% body weight (BW) day^?1) on growth performance, production traits and body composition. Twelve 4‐m³ concrete tanks (2 × 2 × 1.25 m, long, width and height) were each stocked with 100 fish and fed diets containing either 25% or 30% crude protein at rates of 1%, 2% and 3% BW daily (2 × 3 factorial experiment). The results revealed that there was no significant increase in growth rate with increasing dietary protein levels, whereas there was significant increase in growth rate with increasing feeding levels (P≤0.05). The same trend was also observed for mean BW (g), mean body length (cm), production rate (kg m^?3), specific growth rate (SGR % day^?1), feed conversion ratio (FCR), condition factor (K) and survival rate (%). The best final mean BW (g), final mean body length (cm), SGR (% day^?1), FCR, K, production rate (kg m^?3) and survival rate (%) were recorded in groups of fish fed with 25% dietary protein at the 2% feeding level. Whole fish fat and energy contents were not significantly influenced (P>0.05) by protein levels and feeding levels. Protein and ash contents were significantly (P≤0.05) influenced by feeding level, but not by dietary protein level. Economic evaluation indicated that dietary protein 25% (diet A) at the 2% BW day^?1 feeding level was the most cost‐effective and affordable feed strategy for farmers. We conclude that a 25% protein diet fed at 2% BW day^?1 is recommended for adult Nile tilapia reared in concrete tanks.     

Growth and feeding of white steenbras, Lithognathus lithognathus (Cuvier) (Sparidae), under experimental culture conditions

Growth and feeding of white steenbras, Lithognathus lithognathus (Cuvier). under culture conditions was determined to assess its suitability for mariculture. Ration size ranged from 4.50% to 11.52% and from 1.67% 4.00% dry body weight for small (28 ± 2 g) and large (250 ± 23 g) fish, respectively. Condition factor (K) ranged from 1.19 to 1.35 and from 2.00 to 2.19 for small and large fish, respectively. Specific growth rate (SGR) at 16°C was 0.60% day^?1 for 28-g fish, 0.29% day^?1 for a 74-g fish, and 0.19% day^?1 for a 250-g fish. Gross conversion efficiency (GCE) was inefficient at high feeding levels (21.3%) compared with low feeding levels (32.6%). Proximate body composition in terms of moisture, protein. lipid, ash and energy were not significantly affected by feeding regime or temperature (P > 0.05). The experiments indicate that feeding regimes should be maintained at relatively low levels to obtain optimum K, GCE and SGR, and to avoid over-feeding and food wastage. It was concluded that L. lithognathus could be a suitable candidate for mariculture.     

Effects of stocking density and feeding duration in cage‐cum‐pond‐integrated system on growth performance,water quality and economic benefits of Labeo victorianus (Boulenger 1901) culture

We evaluated the effect of varying cage stocking density (60, 90 and 120 fish m^?3) and feeding duration (10, 30 and 60 min) in a cage‐cum‐pond‐integrated system on growth performance, water quality and economic benefits in Labeo victorianus culture. Interactions between stocking density and feeding duration significantly (P < 0.05) affected the fish growth performance and yields in the cages‐cum‐pond system. Stocking density of 60 fish m^?3 resulted in the highest growth in cages and in ponds regardless of the feeding duration, but produced lower yields than at stocking density 90 fish m^?3_. The lowest Apparent Food Conversion Ratio (AFCR) in cages occurred at stocking density of 60 fish m^?3 and feeding duration of 30 min. Growth performance in the open ponds declined with increased feeding duration of the caged fish. Survival in cages and in the open ponds decreased with increased cage density, but was not affected by feeding duration. Low dissolved oxygen were recorded, at stocking density of 120 fish m^?3, the lowest DO occurred when feeding of caged fish lasted 60 min. Growth performance, water quality and economic benefits in Labeo victorianus culture positively respond to interaction between stocking density and feeding durations.     

Preliminary study on the effects of exclusion of wild fauna from aquaculture cages in a shallow marine environment

Previous investigations into the environmental impacts at a shallow-water oligotrophic marine experimental cage aquaculture site in Western Australia have found no accumulation of organic material, and limited changes in macrofaunal communities. It was hypothesised that wild fish populations in the area consumed particulate wastes emanating from the cage, thus reducing the benthic impacts. An experiment was designed to quantify the accumulation of organic material on the seabed occurring in the presence and absence of wild fauna. Three treatments were arranged in duplicate, cages without exclusion nets (normal situation) (CAGE-FISH); cages surrounded by a 35-mm mesh exclusion net (preventing wild fish access to the sea bed and water column near the cage) (CAGE-FISH-EXCL); and empty cages surrounded by exclusion nets (to control for effects from the exclusion net) (CAGE-EXCL). In addition, four reference sites without cages (REF) were sampled. Following baseline sampling, rainbow trout (Oncorhynchus mykiss) were stocked into the CAGE-FISH and the CAGE-FISH-EXCL treatments at an initial stocking density of 2.4 kg m⁻³. The experiment was terminated after 62 days, at a final stock density of 5.6 kg m⁻³. Sampling found significantly greater accumulation of nutrients and fine sediments under the cages enclosed in the exclusion net than in other treatments and sites. Levels of organic carbon deposition at cages with exclusion nets was found to be 4.5±1.0 g C m⁻² day⁻¹ (mean±S.E.) compared to 0.7 to 1.1 g C m⁻² day⁻¹ at control and reference sites.The accumulation of nutrients at the CAGE-FISH-EXCL sites was correlated to distinct changes in macrofaunal community composition, with a sharp increase in overall macrofaunal abundance and a growing dominance of capitellid polychaetes. Based on a comparison between sedimentation rates within and outside excluded areas, the proportions of the total sedimenting nutrients consumed by wild fish were calculated to be 40% to 60%. It was concluded that in the natural coastal system of Western Australia or comparable environments, wild fish are potential important consumers of cage aquaculture waste materials. The fact that sediment C, N and P did not increase below cages with fish and no exclusion nets suggests that the benthic fauna, including surface grazing fish, at these sites were able to assimilate much of the remaining total sedimentary nutrients.     

Fin damage and growth parameters relative to stocking density and feeding method in intensively cultured European perch (Perca fluviatilis L.)

We evaluated the relationship of stocking density to survival, growth performance and fin condition of European perch Perca fluviatilis with hand feeding and self-feeders. Hand-fed perch (body weight 19.1 ± 5.1 g and total length 107 ± 9 mm) were reared at 0.5, 1.0, 1.5 and 2.0 fish/L. Self-feeding perch (body weight 25.4 ± 3.9 g and total length 128 ± 7 mm) were reared at stocking densities of 0.6, 1.0 and 1.4 fish/L. Pond-reared perch served as a comparison group for fin damage assessment. We found no differences in survival rate among stocking densities with either feeding method. Hand-fed fish displayed the highest weight gain and SGR at stocking density of 0.5 fish/L. The self-feeding fish showed a non-linear association of weight gain with stocking density with the highest growth at 1.0 fish/L. Fin length was noticeably greater in pond-reared fish compared with RAS-reared fish regardless of feeding method. In both experiments, fin length relative to standard length showed a negative relationship with stocking density, with pectoral fins showing the greatest effect. Fin condition deteriorated with increasing stocking density, and growth was highest at 0.5 and 1.0 fish/L in hand-fed and self-feeding fish, respectively.     

The effect of feed supply rate on growth of juvenile perch (Perca fluviatilis)

This study investigates the effect of the feed supply rate within a meal on growth of juvenile perch (Perca fluviatilis). Groups of PIT-tagged, feed-trained juvenile perch (12 g) were held in 100-L tanks at 18 °C, under a 24L:0D photoperiod and fed five meals per day in excess. Feed was applied at rates of 1.2 (Low), 4.2 (Medium) and 14.3 (High) pellets fish⁻¹ min⁻¹ during two periods, each of 50 days. Cumulative meal-time per day ranged from 10 to 225 min. Specific growth rates (SGR) in the two periods were positively correlated, indicating a consistent individual growth performance. There was growth dimorphism between the sexes. Females grew about 20% faster than males, resulting in final mean weights of ≈ 87 and 58 g respectively. Autopsy revealed differences in sex ratios between treatments and the effect of feeding rate was analysed according to sex. There was a tendency for fish fed at the lowest rate to have a higher SGR than fish in other treatments, both for females (L = 1.98 ± 0.0, M = 1.84 ± 0.08, H = 1.88 ± 0.19% bw day⁻¹) and males (L = 1.68 ± 0.01, M = 1.55 ± 0.16, H = 1.57 ± 0.02% bw day⁻¹). Fish fed at the lowest rate also tended to have the lowest feed conversion ratio (L = 0.88 ± 0.05, M = 1.02 ± 0.11, H = 1.04 ± 0.10) but the effects were not significant. These results suggest that juvenile perch can feed efficiently under a range of conditions.     

Feeding behaviour and growth of lumpfish (Cyclopterus lumpus L.) fed with feed blocks

The aim of this project was to investigate if lumpfish can be fed using specially designed feed blocks instead of regular fish feed pellets. Two studies were performed. In Part I different designs of feed blocks were introduced and fish observed with underwater cameras to record feeding behaviour. Results indicate that lumpfish require feed blocks with grooves in order to graze from them and that the acclimation period is relatively short (2–4 hr) before the fish will use them as a feed source. In the second part of the project two duplicate groups of lumpfish with an initial mean (±SD) weight of 125.4 ± 45.7 g were individually weighed and randomly distributed into six 3.5 m³ circular flow‐through tanks with 45 fish in each tank. Fish in three tanks were fed using feed blocks with grooves and fish in three tanks were fed using a regular commercially available lumpfish extruded feed. Both groups received a daily feeding rate of 2% body/weight. From day 14 onwards, fish fed with marine pelleted feed had a significantly higher mean weight compared to fish fed with feed blocks. Although not significant, the condition factor was higher in the feed block group during the study period. Results from this study show that lumpfish will readily graze from feed blocks if they are presented in a way that allows them to do. In addition, the acclimation period required before the fish will utilize them appears to be short thus potentially allowing for their use in commercial salmon cages.