Assessment of the removal efficiency of fish farm effluents by grey mullets: a nutritional approach

A field study was carried out to assess the use of the bottom‐feeding grey mullet (Mugil cephalus) within benthic enclosures as a means to reduce the benthic impacts of a net cage fish farm in the Gulf of Aqaba, Red Sea. Five experimental 1‐m³ net‐cage enclosures were stocked with 12 grey mullets each (fish weights 50, 70 or 144 g). The enclosures had no bottom and the mullets had access to the enclosed organically enriched sediments and to particulate matter (PM) falling from the overlying cages. Sediment traps were used to quantify and qualify the PM falling from the fish farm to the sea floor. Simultaneously, a feeding trial was performed with mullets (50 and 70 g) in experimental tanks. In order to estimate the potential growth rate and to quantify energy and protein requirements, the fish were fed a formulated diet with known composition. After approximately 70 days at sea, mullets in the enclosures had used up all the available food in the sediment and gained up to 0.78 g day^?1 fish^?1. Applying the values for energy and protein requirements for maintenance and growth derived from the experimental trial, estimates indicated that the grey mullets effectively removed 4.2 g organic carbon, 0.70 g nitrogen and 7.5 mg phosphorus kg^?1 mullet m^?2 day^?1 from the organically enriched sediment. Thus deployment of grey mullets may be an efficient means to improve the quality of sediments below intensive net‐cage fish farms.     

The effect of light intensity on growth of juvenile dusky kob Argyrosomus japonicus (Temminck & Schlegel 1843)

South African juvenile dusky kob Argyrosomus japonicus are more abundant in turbid estuaries than in clear marine‐dominated estuaries. Turbidity can reduce light penetration into the water and create an environment different from that experienced by fish under culture conditions in mechanically filtered clear water. In order to optimize rearing conditions of this species, the effects of light intensity (23–315 lx) and feeding method (restricted ration vs. feeding to apparent satiation) on growth and food conversion ratio (FCR) of juvenile A. japonicus were assessed in a 56‐day growth trial. Fish weight increased from 7.2±1.6 to 41.9±10.2 g fish^?1 at a growth rate of 3.25% body weight day^?1. Light intensity did not significantly affect growth or FCR. Feeding method did not significantly affect growth rate, but average FCR was significantly better in treatments fed a ration of 3.6% body weight day^?1 than in treatments fed to apparent satiation. Therefore, a light intensity range of 23–315 lx can be used to culture dusky kob juveniles. The better FCR in fish fed a restricted ration suggests that a ration of 3.6% body mass day^?1 allowed good growth of juvenile dusky kob.     

Suitability of cage culture for Pacific abalone Haliotis discus hannai Ino production in China

Pacific abalone (Haliotis discus hannai Ino) aquaculture is a thriving industry in China. This study describes a novel submerged cage culture system for abalone rearing in Fujian, South China. The cage consisted of five vertical slots that were oriented perpendicular to the flow of water. The slots were separated by six vertically connected plastic plates for abalone attachment and shelter at the bottom of the cage. Experiment 1 was designed to determine the appropriate stocking density at the start of the abalone sea‐based production cycle. Eight‐month‐old hatchery reared and size‐graded juveniles were transferred to the sea‐based culture system. For different stocking densities, shell length of juveniles obtained in this novel culture system on 2, 3.5 and 5 months, respectively, was compared with shell lengths obtained in a traditionally multi‐tier basket culture system. In Experiment 2, daily growth rates (DGRs) in shell length and biomass in terms of wet weight of 2‐year‐old abalones reared in cage and tiered basket culture systems were compared over a 6‐month period. Results of Experiment 1 showed that growth of abalone in the cage culture system is density‐dependent; the mean final shell length of juveniles obtained was 6.7–15.9% higher than in tiered baskets system even at the same initial stocking density. In Experiment 2, DGRs in shell length of 53.83–78.38 μm day^?1 obtained in cage system were significantly higher than that in tiered baskets (P < 0.01). And in terms of wet weight biomass, it was 1.48–3.01 times higher in the cage system compared with the traditional system. Abalone survival was more than 87.5% in both culture systems in both experiments. Advantages of the newly established cage culture system included better growth performance of the animals reared and potential improvement of rearing conditions, such as improved water flow velocity and dissolved oxygen.     

Growth and reproduction of the lion's paw scallop Nodipecten subnodosus in a suspended culture system at Guerrero Negro lagoon,Baja California Sur,Mexico

The lion's paw scallop, Nodipecten subnodosus (Sowerby) has considerable aquacultural potential due to its fast growth and large adductor muscle. Prior investigations throughout northwestern Mexico's littoral have reported highly variable growth rates; furthermore, no studies are available of the environment on growth and gametogenesis in this species under culture conditions. This investigation assesses the effect of food availability and temperature on the growth and gametogenesis of N. subnodosus in a suspended culture system at Guerrero Negro lagoon, Mexico. After 1 year of cultivation, N. subnodosus reached 69.13 mm in shell height (SH) (0.196 mm day^?1, 14 months old). Two significant growth spurts were observed: over the two first months of culture (August and September 2001, mean growth rate 0.4 mm day^?1) and in September 2002 (0.3 mm day^?1), both related to high temperatures and chlorophyll a concentrations. The onset of gametogenesis occurred in April 2002, with an increase in temperature (10‐month‐old scallops, 54.5 mm SH). The first spawning occurred in October and November (86.2 and 93 mm SH), with peak temperatures. These results, together with the analysis of previous reports, indicate that N. subnodosus has a higher preference for temperate areas; therefore, the Guerrero Negro lagoon appears to be a suitable site to culture this species.     

Polyculture of milkfish Chanos chanos (Forsskal) and the red seaweed Gracilariopsis bailinae (Zhang et Xia) in brackish water earthen ponds

Growth, net production, and survival rates of milkfish cultured with Gracilariopsis bailinae at two stocking density combinations (T₁– 30 fingerlings 100‐m^?2 pond+1‐kg G. bailinae 4‐m^?2 net cage, T₂– 30 fingerlings 100‐m^?2 pond+2‐kg G. bailinae 4‐m^?2 net cage) in brackish water earthen ponds over four culture periods were determined. The control (T₃) was stocked at 30 fingerlings 100‐m^?2 pond. Specific growth and production rates of G. bailinae were also calculated. There were no significant differences in mean growth, survival, and net production rates of milkfish between the three treatments. Irrespective of stocking singly or in combination with G. bailinae, significantly higher mean growth and mean production rates for milkfish were obtained during the third culture period of year 1 than those obtained from the other culture periods. Survival rates were not significantly different among the four culture periods. There were no significant differences in mean specific growth and mean net production rates between the two stocking densities of G. bailinae. Significantly higher mean specific growth and mean net production rates of red seaweed were also obtained during the third culture period of year 1 than those obtained from other culture periods. The production of milkfish and red seaweed was higher during the dry season. Growth rates of milkfish was positively correlated with temperature and salinity, while net production rates were positively correlated with temperature and total rainfall, but was inversely correlated with dissolved oxygen. G. bailinae growth and net production rates were positively correlated with water temperature and salinity. Results show that milkfish can be polycultured with G. bailinae grown in net cages in brackish water ponds at stocking density combination of 30 fingerlings 100‐m^?2 pond+1‐kg G. bailinae 4‐m^?2 net cage.     

Efficient utilization of dietary lipids in Octopus vulgaris (Cuvier 1797) fed fresh and agglutinated moist diets based on aquaculture by‐products and low price trash species

The aim of this study was to evaluate growth, biochemical composition and dietary nutrients utilization in Octopus vulgaris fed on four diets based on bogue Boops boops, from different origin and in two presentations: fresh discarded bogue (aquaculture by‐product) (DB‐f), fresh wild bogue (low price trash species) (WB‐f), discarded bogue agglutinated moist diet (DB‐m) and wild bogue agglutinated moist diet (WB‐m). Diets based on DB showed higher lipid content (19–26% dw) than those based on WB (5–6% dw). Octopuses fed on DB‐based diets showed higher growth (1.5–1.9% day^?1) and higher protein efficiency ratio (0.64–0.69) than those fed on WB‐based diet (1.1–1.5% day^?1 and 0.36–0.37 respectively), which suggests good utilization of dietary lipids and also a possible protein sparing effect by lipids in O. vulgaris. Octopuses fed on diets presented fresh showed a higher growth (1.9–1.5% day^?1) and a higher feed efficiency (62–65%) than those fed on agglutinated diets (1.1–1.5% and 52–60% day^?1 respectively). Regarding fatty acids, the digestive gland clearly reflected dietary lipid and fatty acid profile, while muscle showed a more stable composition. Low dietary ARA content reflected in octopus tissues, especially in specimens fed on DB‐based diets, which did not seem to affect growth during the experimental period.     

Growth performance of Trichogaster pectoralis Regan in intensively cultivated rice fields

Trichogaster pectoralis Regan is often cultured successfully in rice fields in South‐east Asia. However, since the advent of high‐yielding rice varieties and intensive rice cropping, several reports suggest poorer growth performance of the species. In this paper, we investigated the growth performance of T. pectoralis in rice–fish systems characterized by intensive rice culture and extensive to semi‐intensive polyculture of Oreochromis niloticus (L.), Cyprinus carpio L. and Barbodes gonionotus (Bleeker). In these systems, T. pectoralis recorded negative net productions. This was mainly the result of a negative specific growth rate (SGR) when fish had to stay in the trench (?0.519% body weight day^?1) or when fish had free access to the rice crop (?0.081). Only when harvested rice plants were allowed to generate new tillers (ratooning) did T. pectoralis perform slightly better (0.453% body weight day^?1). The SGR of T. pectoralis was low owing to a lack of food in intensive rice systems. The other species, all with SGR values higher than 1% body weight day^?1, clearly had a competitive advantage over T. pectoralis. We concluded that intensification of rice cropping did indeed result in poor T. pectoralis growth. Successful T. pectoralis culture is only possible in areas of traditional rice cropping.     

Effect of feeding time on dietary protein utilization and growth of juvenile Senegalese sole (Solea senegalensis)

The present study aimed to determine the effect of feeding time on growth and nitrogen excretion in juvenile sole. An 84‐day growth trial was conducted, in which food was supplied to three triplicate groups of juvenile Senegalese sole (3 g wet weight) at different schedules – diurnal, nocturnal and mixed. At the end of the growth trial, ammonia and urea excretion was assessed during a 24 h cycle. Improved growth (1.3% vs. 0.9% day^?1, specific growth rate), higher nitrogen retention (0.35 vs. 0.27 g N kg^?1 day^?1), lower ammonia excretion (209 vs. 272 mg N‐NH₄ kg^?1 day^?1) and lower total nitrogen excretion (278 vs. 352 mg N kg^?1 day^?1) were found in daytime‐fed fish compared with night‐fed fish. Fish in the mixed feeding regime showed intermediate values of ammonia and total nitrogen excretion, but did not differ from day‐fed fish regarding the other parameters. Results indicate that juvenile sole at a period of their life cycle appear to use more efficiently dietary protein for somatic growth under a diurnal than under a nocturnal feeding regime. This suggest that at least during a time‐window in the juvenile rearing a diurnal feeding regime might be more effective in the production of this species.     

Pond farming of Nile tilapia, Oreochromis niloticus (L.), in northern Cameroon. Feeding combinations of cottonseed cake and brewery waste in fingerling culture, hand-sexed male monosex culture, and mixed culture with police-fish, Clarias gariepinus (Burchell)

Twelve production trials were analysed retrospectively, covering three different rearing methods in which Nile tilapia, Oreochromis niloticus (L.), were fed with combinations or cottonseed cake and brewery waste. Highest extrapolated net pond productions, including tilapia recruits, were obtained in tilapia fingerling rearing (W₀ <10 g; 11.8 t ha^?1 year^?1). Stocking African catfish, as police-fish (0.2 catfish m^?2) in mixed tilapia (W₀ > 90 g) culture was effective in controlling tilapia recruitment, but net pond production was low (4.1 t ha^?1 year^?1). Hand-sexing of male tilapias (W₀ > 90 g) only limited recruitment but resulted in a significantly higher net pond production (8.6 t ha^?1 year^?1) than in mixed culture. Extrapolated marketable production in the treatment stocked with hand-sexed tilapia males (tilapia only) was also higher than the extrapolated marketable production in the mixed culture treatment (tilapia and catfish combined), although this difference was not significant. Extrapolated net pond production and extrapolated net tilapia production were both significantly correlated to the daily feeding rate of cottonseed cake but not to the daily feeding rate of brewery waste. The high relative FCRs of the feed mixture were probably due to the brewery waste.     

Effects of feeding levels on growth performance,feed utilization,body composition and apparent digestibility coefficients of nutrients for juvenile Chinese sucker,Myxocyprinus asiaticus

An experiment was conducted to determine effects of feeding levels on growth performance, feed utilization, nutrient deposition, body composition and apparent digestibility coefficients (ADCs) of nutrients for juvenile Chinese sucker (initial weight, 11.77±0.22 g). Chinese sucker were fed a practical diet from 0% (starvation) to 4.0% (at 0.5% increments) body weight (bw) day^?1 for 8 weeks. The results showed that growth performance, feed utilization, nutrient deposition, body composition and ADCs of dry matter, protein and energy were significantly (P<0.05) affected by feeding levels. Survival was the lowest for the starvation group. Final mean body weight, growth rate, thermal‐unit growth coefficient (TGC) increased with feeding rate from 0% to 3.0% bw day^?1 (P<0.05) and showed no significant differences above the level (P>0.05). Feed conversion rate was significantly lower at a feeding level of 2.5% bw day^?1 than above and below the level (P<0.05). Protein efficiency ratio was markedly highest at the 2.5% bw day^?1 ration level (P<0.05). Fish fed at the feeding level (1.0% bw day^?1), which represented a maintenance ration (energy gain was less than 2.27 kJ fish^?1 day^?1), showed positive protein deposition but negative lipid deposition. This indicates that fish fed a maintenance ration mobilize body lipid reserve to support protein deposition. Lipid contents of whole body, muscle and liver increased with increasing feeding rates from 0.5% to 3.0% bw day^?1 and showed no significant differences above the level (P>0.05). Protein contents of whole‐body composition increased with feeding rate from 0.5 to 3.0% bw day^?1 (P<0.05) and showed no significant differences above the level (P>0.05), whereas muscle and liver remained relatively stable with the different ration amount with the exception of fish fed a ration of 0.5% bw day^?1, at which Chinese sucker possessed significantly lower body protein concentration (P<0.05). The ADCs of dry matter, protein and energy decreased with increasing feeding levels from 0.5% to 3.0% bw day^?1 and then remained relatively constant over the level. Based on the broken‐line regression analysis using WG data, the optimum and maintenance feeding levels for Chinese sucker were 3.10% bw day^?1 and 0.45% bw day^?1 respectively.     

Growth of redclaw crayfish Cherax quadricarinatus (Von Martens 1868) (Decapoda: Parastacidae) juveniles fed isoproteic diets with partial or total substitution of fish meal by soya bean meal: preliminary study

Growth of juvenile redclaw Cherax quadricarinatus fed 400 g kg^?1 crude protein isoproteic diets substituting fish meal with soya bean meal at various levels (250, 500, 750 and 1000 g kg^?1) was evaluated under laboratory conditions. Juvenile crayfish were reared individually in 1‐L plastic containers for 56 days. Total survival was recorded for all treatments at the end of the experiment. There were no significant differences (P > 0.05) for the specific growth rate among the treatments, although the animals fed with the control diet (100% fish meal) obtained the highest mean daily weight gain (0.055 g day^?1), individual final weight (4.12 g), molts per individual (0.04 molts day^?1) and molting frequency (23.57 days) values at the end of the experiment. Dietary inclusion of soya bean meal at the tested levels hampered the C. quadricarinatus juvenile growth.     

Response of the tropical spiny lobster Panulirus ornatus to protein content of pelleted feed and to a diet of mussel flesh

In an 8‐week growth experiment, juvenile spiny lobsters (Panulirus ornatus) grew best on a feed containing at least 610 g kg^?1 crude protein on a dry matter basis (DM) and a digestible protein to digestible energy ratio of 29.8 mg kJ^?1. The study entailed a six treatment by four replicate randomized block experiment with 222 wild‐caught P. ornatus of mean initial weight (±SD) of 2.5 ± 0.19 g. The lobsters were fed one of five isolipidic feeds (approximately 130 g kg^?1 DM) in which the crude protein was serially incremented between 330 and 610 g kg^?1 DM, or a reference diet comprising the flesh of frozen green‐lip mussels. Lobsters fed the pelleted feeds had high survival (79 ± 4.5%) and responded to increasing dietary crude protein content with progressively higher growth rates, with the daily growth coefficient improving from 0.72% day^?1 with 330 g kg^?1 crude protein to 1.38% day^?1 with 610 g kg^?1 crude protein. Both growth rate and survival were low with the mussel diet (0.80% day^?1and 41 ± 4.5%, respectively). These results demonstrate that tropical spiny lobsters grow well when fed high‐protein, high lipid, pelleted feeds, but feeding on a sole diet of freshly thawed green‐lip mussels was unsatisfactory.     

Scale matters: performance of European sea bass,Dicentrarchus labrax,L. (1758), reared in cages of different volumes

The effects of rearing volume on on‐growing European sea bass performance and stress parameters were investigated for the first time in a pilot aquaculture farm. Fish were held under the same initial stocking densities in triplicate net‐pen cages of different sizes (1.4, 45 and 252 m³) for a period of 8 months. Results showed significant differences among the experimental groups in most parameters tested, with better performance in the two larger rearing volumes. In particular, growth rate showed a linear association with rearing volume, being 0.68 g day^?1 for the large cage group, 0.56 g day^?1 and 0.32 g day^?1 for the medium and the small groups respectively. The feed conversion ratio and per cent survival (%) were also better in the large cage group. Fish reared in the small and medium‐sized cages showed higher plasma cortisol concentrations than those reared in large cages, which showed low basal cortisol concentrations. Additionally, after an acute chasing stress challenge, fish in the large and small groups, but not the medium group, showed increased cortisol concentrations. Differences also occurred in the ratio of the expression of cortisol receptors, namely the mineralocorticoid (mr) and glucocorticoid receptors (gr). In specific, the ratio of mr to grmRNA expression in the liver was higher in fish reared in the small cages. These findings verify that experimental scale significantly affects experimental results and is a critical factor for the interpretation of results.     

The use of alternative diets to culture juvenile cuttlefish,Sepia officinalis: effects on growth and lipid composition

The effects of feeding three natural frozen diets, grass shrimp (Palaemonetes sp.), crayfish (Procambarus clarkii) and fish (Sardina pilchardus) and two semi‐humid artificial diets (based on fish or shrimp powder) to the cuttlefish, Sepia officinalis, were analysed. Growth rate and feeding rate [FR; % body weight (BW) day^?1] and food conversions (FC, %) were determined. Cuttlefish fed shrimp grew larger (3.8% BW day^?1) and had the highest FC, followed by those fed crayfish, and sardine. The highest FR was obtained for cuttlefish fed crayfish (10.5% BW day^?1). Although both artificial diets were accepted, none produced growth. Digestive gland‐to‐body weight ratio (DG/BW ratio) was calculated for animals fed each diet. A positive correlation (r = 0.94) between cuttlefish ingestion FR and DG weight was obtained. Mortality occurred mainly during the last week, and some cannibalism occurred among cuttlefish fed artificial diets. Finally, lipid composition of diets, DG and mantle of each group were analysed. Sardine diet was characterized by high levels of triacylglycerol (TG), whereas the main difference between shrimp and crayfish was the higher n‐3/n‐6 ratio found in shrimp. Changes in the lipid composition of DG were related to diet, but did not correlate with growth data. A strong loss of TG in the DG of artificial diets groups was notable. No differences in mantle lipid composition among the natural diets were found, but artificial diet groups showed higher contents of neutral lipids in their mantle respect to natural diets. According to results obtained, crayfish (P. clarkii) could be used as an alternative prey for rearing S. officinalis compared with shrimp. Artificial diets showed the worst effects in growth and mortality as well as the stronger influence on DG and mantle lipid composition of cuttlefish.     

Nursery rearing of the Asian catfish, Clarias macrocephalus (Günther), at different stocking densities in cages suspended in tanks and ponds

Growth and survival of hatchery‐bred Asian catfish, Clarias macrocephalus (Günther), fry reared at different stocking densities in net cages suspended in tanks and ponds were measured. The stocking densities used were 285, 571 and 1143 fry m^?3 in tanks and 114, 228 and 457 fry m^?3 in ponds. Fish were fed a formulated diet throughout the 28‐day rearing period. Generally, fish reared in cages in ponds grew faster, with a specific growth rate (SGR) range of 10.3–14.6% day^?1, than those in cages suspended in tanks (SGR range 9–11.3% day^?1). This could be attributed to the presence of natural zooplankton (copepods and cladocerans) in the pond throughout the culture period, which served as additional food sources for catfish juveniles. In both scenarios, the fish reared at lower densities had significantly higher SGR than fish reared at higher densities. In the pond, the SGR of fish held at 228 and 457 m^?3 were similar to each other but were significantly lower than those of fish held at 114 m^?3. The zooplankton in ponds consisted mostly of copepods and cladocerans, in contrast to tanks, in which rotifers were more predominant. Per cent survival ranged from 85% to 89% in tanks and from 78% to 87% in ponds and did not differ significantly among stocking densities and between rearing systems. In conclusion, catfish nursery in cages suspended in tanks and ponds is density dependent. Catfish fry reared at 285 m^?3 in tanks and at 114 m^?3 in ponds had significantly faster growth rates than fish reared at higher densities. However, the desired fingerling size of 3–4 cm total length for stocking in grow‐out culture can still be attained at stocking densities of 457 m^?3 in nursery pond and 571 m^?3 in tanks.     

Growout production of camouflage grouper, Epinephelus polyphekadion (Bleeker), in a tank culture system

Growout production of the camouflage grouper, Epinephelus polyphekadion (Bleeker), in a 10-m³-capacity fibreglass tank culture system was evaluated, using hatchery-produced fingerlings (56-59 g initial weight) at stocking densities of five, 15 and 45 fish m^?3. During the first 9 months of a 12-month growout period, the fish were fed twice a day with a moist pellet feed containing 40.9% protein. From month 10 onwards until harvest, the fish were fed moist pellets in the morning and trash fish in the evening at a 1:1 ratio. The final weight of fish at harvest was up to 900 g, with mean weights of 544.6 ± 170.72 g at five fish m^?3, 540.2 ± 150.82 g at 15 fish m-^?3 and 513.3 ± 134.52 g at 45 fish m^?3. The results showed no significant differences (P > 0.05) in growth rate and fish size between the different stocking densities tested. The average daily growth rate ranged from 0.62 to 3.38 g fish^?1 day^?1, with mean weights of 1.49 ± 0.74 g fish^?1 day^?1 at five fish m^?3 through 0.53 to 2.38 g fish^?1 day^?1, 1.32 ± 0.57 g fish^?1 day^?1 at 15 fish m^?3 to 0.48-3.32 g fish^?1 day^?1 and 1.31 g fish^?1 day^?1 at 45 fish m^?3 stocking density. Although up to 100% survival was observed at the lowest stocking density, the survival rate significantly decreased (P < 0.05) with increasing stocking density. The food conversion ratio (FCR) significantly decreased (P <0.05) with increasing stocking densities, showing efficient feed utilization with increasing stocking densities of E. polyphekadion. The FCR averaged 2.1 at a stocking density of 45 fish m^?3. The yield in terms of kg fish produced m^?3 of water used in the culture system significantly increased (P < 0.001) from five to 45 fish m^?3. The yield averaged 17.3 ±0.53 kg m^?3 at a stocking density of 45 fish m^?3. The present results show that the present tank culture system could sustain more biomass in terms of increasing fish stocking densities. The growth performance of E. polyphekadion observed during this investigation has been reviewed with other grouper species.     

The effect of food type (formulated diet vs. natural) and fish size on feed utilization in common sole,Solea solea (L.)

This study compares the effect of food type (formulated diet vs. natural food) and fish size on protein and energy utilization efficiencies for growth in common sole, Solea solea (L.). Replicate groups of common sole (mean initial body weight ± SD was 45.7 g ± 2.1 and 111.2 g ± 4.2) received the diets at five (natural feed) or four (formulated diet) feeding levels. The protein utilization efficiency for growth (k_gCP) was higher (P > 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.40 and 0.31). Likewise, the energy utilization efficiency for growth (k_gGE) was higher (P = 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.57 and 0.33). The protein maintenance requirement was not different between food types (P = 0.64) or fish size (P = 0.41) being on average 0.82 g kg^?0.8 day^?1. The energy maintenance requirement was not different between food type (P = 0.390) but differed between fish size (P = 0.036). The gross energy maintenance requirement of small common sole was 35 kJ g^?0.8 day^?1. The gross energy maintenance requirement of large common sole was 25 kJ g^?0.8 day^?1. In conclusion, the low growth of common sole fed formulated diets was related to reduced feed utilization.     

Inter‐ and intra‐individual variability in growth and food consumption in pikeperch,Sander lucioperca L., larvae revealed by individual rearing

We examined short‐term, inter‐ and intra‐individual variability in rates of growth and food consumption in fish early life stages to gain a mechanistic understanding of why larvae in the same environments often grow at vastly different rates. We made parallel measurements of growth rate in standard length (GR_SL) and food consumption rate (C), and provide estimates of weight growth rate (GR_DW) and gross growth efficiency (GGE = 100*GR_DW/C) of individually reared larvae of pikeperch, Sander lucioperca L., fed Artemia nauplii at 20°C and a salinity of 2.0 g L^?1. Within two trials, GR_SL, C and GGE were obtained for 108 larvae over a maximum period of 28 days. Mean (±SD) initial size, GR_SL, C and GGE were 19.49 (9.19) mm, 0.68 (0.21) mm day^?1, 0.85 (0.44) mg day^?1 and 36.5 (10.2)% respectively. The vast majority (91%) of the variability in growth was explained by differences in food consumption. When isolated from conspecifics for 28 days, relatively small larvae grew faster than relatively large ones, partially mitigating initial differences in size‐at‐age.     

High feeding and growth rates in common octopus (Octopus vulgaris) fed formulated feeds with an improved amino acid profile and mixture of binders

Four semi‐moist formulated feeds were supplied to Octopus vulgaris subadults (664 ± 70 g; 18.4 ± 0.7°C) in two different experiments. In the experiment #1, two diets were prepared with a new mixture of binders (gelatine 150 g kg^?1, starch 100 g kg^?1 and gum 50 g kg^?1). The GEL15‐Squid and GEL15‐Hake feeds included 100 g kg^?1 freeze‐dried squid (Todarodes sagittatus) or hake (Merluccius sp.) respectively. Both feeds showed low water disintegration rates at 24 h (13.6–15.0% dry weight). The specific feeding rate was higher in animals fed GEL15‐Hake (2.7%BW day^?1), but the growth and feed efficiency were significantly better in animals fed GEL15‐Squid (1.4%BW day^?1 and 61.2% respectively; P < 0.05). The proximate composition of the digestive gland, carcass and whole animals was similar. In the experiment #2, the GEL15‐Squid amino acid profile was improved by replacing 50 g kg^?1 gelatine by 50 g kg^?1 freeze‐dried squid (GEL10‐Squid) or freeze‐dried fish (GEL10‐Fish). These feeds showed higher water disintegration rates (31.7–36.3% dry weight). The feeding rates (2.2–2.3%BW day^?1), growth (1.5%BW day^?1) and feed efficiency were similar for both diets. Total lipids were higher in the digestive gland and whole animals fed GEL10‐Fish diet (P < 0.05). Future effort could be directed towards alternative binders that allow improve amino acid balance with a minimum gelatine content or even supplementation trials including essential amino acids.     

Preliminary observations on the tank and pond culture of the glass eels of the Australian shortfin eel, Anguilla australis Richardson

There is expanding interest in the culture of the Australian shortfin eel Anguilla australis Richardson; however, there is a lack of fundamental biology and husbandry information necessary to further develop an industry within Australia. The present study was undertaken to gain a preliminary understanding of basic husbandry requirements for rearing of juvenile A. australis (glass eels and elvers) in tanks and earthen ponds. Newly caught glass eels were successfully acclimated to culture conditions. During tank culture trials, specific growth rates (SGR) and survival rates ranged from ?2.1 to 2.8% day^?1 and 52% to 100% respectively. Glass eels weaned onto a commercial eel diet exhibited a significantly greater SGR and survival rate than those weaned onto a commercial trout diet. Glass eels weaned onto an eel diet over a 15‐day period grew slightly faster than eels weaned over a 5‐day period, but survival rates were not significantly different for each treatment. SGRs (up to 2.8% day^?1) were significantly higher for glass eels fed at 9 and 12% day^?1 than at 6% day^?1. Stocking densities between 2.5 kg m^?3 and 30 kg m^?3 did not influence either SGR or survival rates. SGRs were significantly higher for glass eels cultured at 25 °C than at lower temperatures. During pond culture trials, SGRs and survival rates ranged from 1.36 to 1.65% day^?1 and 39% to 77% respectively. The SGR and survival rates of juvenile eels stocked into ponds receiving supplementary feeding with a commercial eel diet were not significantly different to those of eels stocked into ponds that did not receive supplementary feeding.