Grow-out culture of tropical abalone, Haliotis asinina (Linnaeus) in suspended mesh cages with different shelter surface areas

Thisstudy investigated the effects of shelter surface area (SSA) on the feeding,growth and survival of the donkey-ear abalone, Haliotisasinina reared in mesh cages (0.38×0.38×0.28m) suspended in flow-through tanks (water volume = 6m³). Cages had sections of polyvinylchloride (PVC) thatprovided shelters with surface area of 0.22 m², 0.44m² and 0.66 m².Hatchery-produced abalone with initial shell length of 32 ± 1mm and wet weight of 7.5 g were stocked at 50individuals cage^?1 that corresponded to stocking densities ofca. 227, 113 and 75 abalone m^?2 of SSA. The ratios of sheltersurface area to cage volume (SSA:CV) were 5.5, 11 and 16.5. Abalones wereprovided an excess red seaweed Gracilariopsis bailinae(= Gracilaria heteroclada) at weekly intervals overa 270-day culture period. Feeding rates (18–20% of wet weight), foodconversion ratio (26–27) and percent survival (88–92%) did notdiffer significantly among treatments (p > 0.05). Body size at harvest rangedfrom 56 to 59 mm SL and 52 to 57 g wet body weightwith significant differences between abalone reared at SSA 0.22m² and 0.66 m² (p < 0.05).Abalone reared in cages with 0.66 m² SSA grewsignificantly faster at average daily growth rates of 132 μm and188 mg day^?1. Stocking densities of 75–113m^?2 SSA in mesh cages suspended in flow-throughtanks resulted in better growth of abalone fed red seaweed.     

Growth and production of the Amazonian tambaqui in fixed cages under different feeding regimes

Experimental culture of the native Amazonian fish tambaqui, Colossoma macropomum, in fixed cages was carried out over a period of 8 months, in Lake Urubu (Rio Grande do Norte, Brazil), to assess the viability of fixed cage culture of tambaqui and to test the influence of diet on growth rates. Nine synthetic net cages (1 m³) were each stocked with 45-day-old fish (mean weight 3 g; mean total body length 51 mm) at a density of 34 fry m^–3. During the first 2 months of culture, fish were fed a balanced formulated feed on an as-fed basis at the rate of 5% body weight day^–1. During months 3–8 this continued for fish in treatment 1 while those in treatment 2 were fed tropical regional fruits, on a wet weight basis at the rate of 5% body wt day^–1. Fish in treatment 3 were given no supplementary feed. Monthly biometric measurements were made on all fish. Fixed cage fish culture was shown to be a viable and simple technique. Survival in all treatments was 100%. With balanced supplementary feed, production was 14.4 kg m^–3, compared with 4.9 kg m^–3 and 2.1 kg m^–3, respectively, in the treatments where fish were fed with fruits and were not given any supplementary feed.     

Production of Australian freshwater crayfish in earthen-based systems using pelleted diets and forage crops as food

Juvenile Cherax destructor (commonly called theyabby) were cultured in earthen-based ponds and tanks for 70–105d, and were fed pellets and/or a forage crop of the perennialwhiteclover, Trifolium repens. Three supplementary feedingstrategies were evaluated. Yabby growth on pellets consistently exceeded (by67–159%) that obtained on clover. Base-line yields for extensiveproduction systems are around 400 kg ha^–1. Thesupplementary addition of T. repens produced yields of 635kg ha^–1 (in ponds) to 1086 kgha^–1 (in tanks). The sequential addition of cut-cloverto tanks stimulated growth to levels approaching those achieved on pellets.Yabbies stocked into ponds at 17 m^–2 and fed 33%protein pellets for 100 d, resulted in a yield of 1117 kgha^–1.Pellet inputs at a rate of 129–249 g m^–2(dry matter) and 38–83 g m^–2 (protein) over70–100 d resulted in acceptable growth and feed utilisationindices. Clover inputs of 534–682 g m^–2 (asdry matter) or 84–177 g m^–2 (as protein)produced reasonable growth rates but poor feed utilisation indices. Aconsiderable quantity of the dry matter and protein content of clover waseitherinefficiently utilised or directed into other production pathways. In tanks,clover inputs from 113–296 g m^–2 (drymatter) and 24–54 g m^–2 (protein) weresufficient to maintain high growth rates for 4 weeks, while in ponds, inputs of21 g m^–2 (dry matter) and 4.3 gm^–2 (protein) were sufficient for 3 weeks. During theearly weeks of production no growth advantage was gained by providing pelletstoanimals cultured in forage-based systems. Forage depletion occurred after3–4 weeks and was probably a major growth limiting factor.     

Abundance and production of the introduced signal crayfish ina British lowland river

In 1984, 40 mature and 100 immature signal crayfish, Pacifastacus leniusculus (Dana), were introduced into the River Great Ouse, England. By 1994, the population had spread up and down stream to occupy an 11.4 km river section. The estimated density and biomass (wet weight) of the population in 1993 were highest in summer at 4.0 m^–2 and 133 g m^–2 respectively, with annual means of 2.2 m^–2 and 82 g m^–2 for crayfish of >30 mm carapace length (CL) in the pool (P2) where the crayfish were originally introduced. Density and biomass were 15 m^–2 and 78 g m^–2, with annual means of 6.1 m^–2 and 33 g m^–2 for crayfish of all sizes in a riffle 300 m downstream from P2. An annual survival rate of 14% was estimated for crayfish >30 mm CL in P2 in 1993. The relative abundance estimated for six riffles and six pools in 1994 showed that crayfish abundance decreased gradually from the original site of introduction both up and down the river. Estimated annual production of crayfish >35 mm CL in P2 for 1993 was 52.58 g m^–2 WW, with a turnover ratio (production/biomass) of 0.44.     

The growth of disk abalone, Haliotis discus hannai at different culture densities in a pilot-scale recirculating aquaculture system with a baffled culture tank

The growth rate of disk abalone, Haliotis discus hannai, energy consumption and changes in water quality were monitored in a pilot-scale recirculating aquaculture system (RAS) for 155 days. Baffles were installed in the RAS culture tanks to enlarge the attachment area and clean out solid waste materials automatically by hydraulic force only. The experimental disk abalones, of shell length 24.5 ± 0.5 mm, were cultured at three stocking densities, 700, 1300 and 1910 individuals/m² bottom area, in triplicate. The abalones were fed with sea mustard, Undaria pinnatifida, once a week. The abalone feed conversion rates and daily growth rates ranged from 24.5 to 25.9 and 0.32 to 0.36%, respectively. Their daily shell increments and survival rates ranged from 67.7 to 78.6 μm/day and 87.6–92.2%, respectively. The growth in weight tended to decrease at a culture density of 1300 individuals/m² bottom area, while shell increments and survival rates were acceptable at this density. The total power consumption for heating was 1185.4 kW, comprising 30.2% of the total power consumption, while the average water exchange rate was only 2.9% per day. The total ammonia nitrogen stabilized below 0.07 mg/L, after conditioning of the biofilter. The NO₂⁻–N, NO₃⁻–N and total suspended solid concentrations were also maintained within acceptable ranges for the normal growth of disk abalone. The use of the RAS with these newly designed culture tanks for disk abalone culture produced 1300 individuals/m² bottom area with a water exchange rate of only 2.9% per day and used about one-tenth of the heat energy of a conventional flow-through system.     

Gill Na+-K+ ATPase, carbonic anhydrase activities and plasma osmotic and ionic variations during smoltification of Atlantic salmon in the north of Portugal

Gill Na⁺-K⁺ ATPase and carbonic anhydrase activities were measured, on a fortnightly basis, from February to July, in 0₊ age Atlantic salmon (Salmo solar), hatched and reared in a freshwater experimental station in Covas, northern Portugal. Plasma osmolarity and ionic composition were also measured. Gill Na⁺-K⁺ ATPase activity increased slowly until April (15–19 moles Pi mg prot^–1 h^–1). From April to late May there was a great increase in activity (19–32 moles Pi mg prot^–1 h^–1) followed by a sharp decline in June (15 moles Pi mg prot^–1 h^–1). In contrast, carbonic anhydrase activity decreased significantly from early April to early June (170-70 moles p-nitrophenol mg prot^–1 h^–1) and increased in late June, suggesting the existence of a compensatory mechanism for the changes in Na⁺-K⁺ ATPase activity. Plasma osmolarity and sodium concentration showed lower levels during the period of high ATPase activity. On the other hand, plasma calcium concentrations showed an increase during the same period (3.47–5.98 mm1^–1 of plasma). A transitory decrease in osmolarity and plasma sodium and chlorine concentrations occurred in March, prior to the surge in Na⁺-K⁺ ATPase activity, suggesting that the physiological changes, characteristic of parr-smolt transformation can be a consequence of this loss of freshwater osmoregulatory capacity.     

The effect of photoperiod, tank colour and light intensity on growth of larval haddock

In two separate experiments, haddock (Melanogrammus aeglefinus) larvae were raised under different photoperiods (24L : 0D or 15L : 9D), or different combinations of tank colour (black or white) and light intensity (1.1 mol s^–1 m^–2 or 18 mol s^–1 m^–2). Growth (0.8% day^–1 in standard length; 2.9% day^–1 in body area) and survival (2%) were not significantly different between photoperiod treatments after 35 days. Larval survival was greater in white versus black tanks after 41 days (2% versus l%, respectively). Growth of larvae was impaired in black tanks at low (1.1 mol s^–1 m^–2) light intensity (0.8% day^–1 in standard length and 2.2% day^–1 in body area versus 1.1% day 21 in standard length and 3.1% day^–1 in body area, for all other treatments). Transmission and reflection of light was low in black tanks at low incident light, and there was very little upwelling light. The resultant poor prey to background contrast probably resulted in larvae being unable to consume sufficient food to sustain a level of growth comparable to that in other treatments.     

Effects of dietary cholesterol on growth, survival and body composition of juvenile abalone Haliotis discus hannai Ino

An experiment was conducted to determine the dietary cholesterol requirement of juvenile abalone Haliotis discus hannai. Eight isoenergetic (18.15–18.61 kJ/g) and isonitrogenous (29.00–29.78% protein) diets, supplemented with 0.00, 0.15, 0.30, 0.45, 0.60, 0.75, 0.90 and 1.05% cholesterol were evaluated. Juvenile abalone (initial weight: 0.67–0.72 g) were reared in a flow-through water system for 24 weeks. During the feeding trial, water temperature was maintained at 14–17 °C, salinity 31–33, pH 7.4–7.9. Abalone fed diet without cholesterol supplementation had the lowest weight gain ratio (WGR, 356.70%). Survival ranged from 98.52 to 100.00% and was not significantly different among treatments. There were no significant effects of dietary cholesterol on composition and cholesterol concentration in the muscle and viscera of abalone. Based on data of WGR using broken-line analysis, the optimal dietary cholesterol requirement of juvenile abalone was found to be 0.23%.     

Growout of hatchery-reared juvenile spotted babylon (<Emphasis Type="Italic">Babylonia areolate</Emphasis> link 1807) to marketable size at four stocking densities in flow-through and recirculating seawater systems

Hatchery reared juvenile spotted babylon, Babylonia areolata, were raised in canvas rearing tanks at four stocking densities (100, 200, 300 and 400 ind. m^–2) in flow-through and recirculating seawater systems until they reached the marketable sizes of 100–140 snails/kg. At all stocking densities, final increments in mean length and weight of snails held in flow-through systems were higher than those in recirculating systems, there was a significant effect (p < 0.05) of culture system on final length and weight. Mean (±SE) survival of snails held at 100 ind. m^–2 in the flow-through system was 100.0 ± 0.1% but was not significantly higher than survival in any other treatment (p > 0.05). Mean survival of snails held in the recirculating system was not significantly lower than at any stocking density in the flow-through system (p > 0.05).     

Replacement of Artemia with Moina micrura in the rearing of freshwater shrimp larvae

The effect of an abrupt change in the live diet of shrimp larvae was investigated by replacing Artemia with Moina micrura. The control treatment consisted of feeding Artemia throughout the rearing period (regime A), while in the other treatments the onset of Moina feeding was arbitrarily chosen at larval stages iv (A3M), vi (A5M), viii (A7M) and x (A9M). No significant differences ( = 0.05) were observed among the treatments during larval production, mean stage development (MSD) and growth of postlarvae. The mean (SD) yields of postlarvae (PL) were 11.97 (1.98), 15.10 (2.92), 14.72(1.56), 13.51 (1.74) and 12.70 (1.40) PL l^–1 respectively for the feeding regimes A3M, A5M, A7M, A9M and A. Up to stage v, the ingestion rate in the Moina treatment was as low as 0.01–0.47 larva^–1 h^–1 compared with that in the Artemia treatment (0.29–1.77 larva^–1 h^–1). However, the ingestion of Moina increased from stage vi–vii onwards.     

Increased winter temperature did not affect completion of smolting in Atlantic salmon

Four groups of 1+ year-old Atlantic salmon, Salmo salar, pre-smolts were reared under various temperature regimes: constant 10 °C from November onwards; ambient temperature until either 15 December or 1 February, then 10 °C; or ambient temperature throughout (control; 2–3 °C November–March). From 20 May onwards, temperature in all groups was ambient, increasing from 10 °C to 17 °C in late July. Rearing temperature had no significant effect on either the timing of completion of smolting, or the duration of the smolt-window. Mean gill Na⁺-K⁺ ATPase activity was not significantly affected by temperature regime; it increased in all groups from < 2.0 mol Pi mg protein^–1 h^–1 (units) in January to 5–7 units in mid-April, then back to < 2.0 units in July. Survival in 96 h, 37) salinity (S) tolerance tests was similar in all groups, increasing from < 10% in early March, to > 90% from mid-April to mid-June, then decreasing to < 20% by early July. Increased winter temperature significantly increased growth and condition factor compared with the control, but during April–May all four groups exhibited similar temporary decreases in condition factor in association with the completion of smolting.     

Effect of Artificial Diets on Growth,Survival and Condition of Adult Cuttlefish, <Emphasis Type="Italic">Sepia officinalis</Emphasis> Linnaeus, 1758

The effects of artificial diets on growth and body condition of adult cuttlefish, Sepia officinalis were tested in two experiments. Supplemented prepared diets (fish myofibrillar protein concentrate) were fed during a 30-day and a 21-day experiments. Growth, feeding rate and food conversion of group-reared cuttlefish were analyzed. The first of these experiments tested four artificial diets, made with increasing levels of lysine, on adult cuttlefish. According to the chemical analysis, diets 1–3 had limiting concentrations of lysine and other essential amino acids (compared to mantle composition of the cuttlefish), while diet 4 was the only one where almost all essential amino acids were present in concentrations similar or higher than the ones present in cuttlefish mantle. A second experiment was conducted by isolating 16 adult cuttlefish individually, and feeding them the same four artificial diets, in order to obtain individual data. During Experiment 1, only the diet with the best chemical score (diet 4) produced growth (p < 0.05), with a mean instantaneous growth rate (MIGR) of 0.30% wet body weight (BW) d⁻¹. Similarly, individually reared cuttlefish fed diet 4 produced the highest IGR’s (0.26, 0.38 and 0.48% BW d⁻¹) and grew larger (p < 0.01). Comparison of cuttlefish fed the artificial diets vs. thawed shrimp and unfed cuttlefish indicated that cuttlefish fed the artificial diets were in an intermediate state. Growth rates obtained with the artificial diets (<0.4% BW d⁻¹) were considerably lower compared to natural prey, live or frozen, reported by other authors.     

Relationship between metabolic rate in vitro and body mass in a marine teleost,porgy Pagrus major

The rate of oxygen consumption of minced whole body was determined volumetrically, as an indication of metabolic rate in vitro (M _{in vitro} ), at 20°C in porgy Pagrus major ranging from 0.0002 g (just after hatch) to 2.9 g (67 days old) in body mass. A triphasic relationship was found between M _{in vitro} of individual fish (l.min^–1) and wet body mass W (g). During the prolarval stage accompanied with the transitional period to the postlarval stage (0.00020–0.00023 g, 0–6 days old), the mass-specific metabolic rate in vitro (M _{in vitro} /W in l.g^–1.min^–1) increased with age (D in days) as expressed by an equation M _{in vitro} /W = 3.88 + 0.74/D. During the postlarval stage (0.00031–0.003 g, 8–22 days old), M _{in vitro} /W remained almost constant, independent of body mass following an equation M _{in vitro} /W = 5.24 W^–0.085. During the juvenile and adolescent stages (0.0047–2.9 g, 30–67 days old), M _{in vitro} /W decreased with increasing body mass following an equation M _{in vitro} /W = 1.66 W^–0.235. These results correspond with the triphasic relationship between metabolism in vivo and body mass observed in intact porgy of 0.0002–270 g (Oikawa et al. 1991). It is concluded, therefore, that the dependence of mass-specific metabolic rate on body size exists in vitro as well as in vivo, during the early stages in the porgy. Based on these results, factors controlling the metabolism-size relationship are discussed.     

Growth and physiological changes in scaled carp and blue tilapia under behavioral stress in mono- and polyculture rearing using a recirculated water system

Growth performance, carcass composition, liver and blood parameters ofscaled carp (C), Cyprinus carpio, and blue tilapia (T),Oreochromis aureus, reared for eight weeks in twomonoculture (100%C and 100%T) and two polyculture (60%C–40%T and40%C-60%T) conditions were investigated. In polyculture 40%C–60%T bothspecies achieved the highest levels of specific growth rate and the lowestlevels of food conversion ratio and carcass lipid content. In addition, theyexhibited the highest values of plasma pO₂ and pH and the lowestvalues of plasma pCO₂, cholesterol and albumin, although thedifferences among treatments were not significant in the case of tilapia.Tilapia showed significantly lower plasma Cl^– levels than underthe other conditions. Carp in monoculture and tilapia in polyculture60%C–40%T had the lowest levels of specific growth rate and significantlyhigher levels of liver lipids and plasma triglycerides than in the other groups.In addition, carp in monoculture exhibited a significantly higher haematocritthan in polyculture. No significant variations among treatments were observedconcerning plasma cortisol, glucose, osmolality, Na⁺, K⁺,HCO₃ ^– andHCO₃ ^–/H₂CO₃ in either species.The combination of scaled carp and blue tilapia, in which blue tilapia were themain species, proved to be the best for both species. It was suggested thatgrowth and physiological changes under mono- and polyculture rearing, in anintensive system, seem to be as a result of a different state of stress relatedto fish behavior.     

Grass carp (Ctenopharyngodon idella) grazing on duckweed (Spirodela polyrhiza)

The aims of this experiment were (1) toquantify the ability of grass carp to processduckweed and (2) to assess indirect changes inwater chemistry and phytoplankton community,caused by grass carp feeding. Yearling grass carp sized 126 ± 7.7 mm (TL) and19.6 g in weight were kept in 9 laminate tanksof 1 m³ for 14 days. Two stockingdensities (2 and 6 fish per m³) anda control without fish were used. Standard growthrate (SGR) of grass carp fed exclusively onduckweed was 0.70% body weight (BW) d^–1and food conversion ratio (FCR) reached 2.0(average water temperature =21.1 ± 3.8 °C). Daily food intakewas 0.2 g of duckweed dry weight (DW), i.e.,1% of average BW of grass carp. SGR ofduckweed growing in 20 × 20 cm floatingenclosures, differed significantly[F(6,2) = 417.9; p = 0.002] between the twostocking densities of grass carp and thecontrol tanks (without fish). Mean SGR ofduckweed was 0.02 g g^–1 day^–1 and thehighest SGR was recorded in the control tanks.Both decrease in NH₄-N and increase inNO₂-N concentrations differedsignificantly between the treatments[F(2,2) = 45.3; p = 0.02 and F(2,2) = 19.2; p = 0.04 respectively]. Changes in other nitrogenand phosphorus components (NO₃-N, TN, TPand PO₄-P) caused by stocking of grasscarp were not significant. Biomass ofphytoplankton, dominated by filamentous algaeand blue-greens, increased proportionately tostocking density of grass carp. Althoughduckweed has a large potential for nutrientremoval, the most common pathway for thenutrients released through grass carp grazingif duckweed cover is loose is theirincorporation into phytoplankton biomass.     

The effect of dietary vitamin E on the pleopodal egg number of Astacus leptodactylus (Eschscholtz, 1823)

The effect of vitamin E on the pleopodal egg number of Astacus leptodactylus (Eschscholtz, 1823) was studied. Crayfish were fed 2% of their total wet weight daily with vitamin E supplemented diets and a control for 70 days. The vitamin E content of the control diet, diet 1, diet 2 and diet 3 were 20 mg kg^–1, 40 mg kg^–1, 80 mg kg^–1 and 160 mg kg^–1 respectively on a dry weight basis. Vitamin E levels of the control and experimental diets were analysed by High Performance Liquid Chromatography. Results showed that diets containing supplemental vitamin E were associated with an increase in the number of pleopodal eggs. The best result was obtained with diet 2 containing 80 mg kg^–1 supplemental vitamin E.     

Quantifying the dietary biotin requirement of the catfish,Clarias batrachus

Asian catfish, Clarias batrachus, were fed semi-purified basaldiets containing 0, 0.1, 0.5, 1, 3 and 5 mg biotin kg^–1diet for 60 days. Fish fed the control diet (no biotin) showed(P < 0.05) higher mortality, lower weight gain, specificgrowth rate (SGR), feed efficiency ratio (FER) and protein efficiencyratio (PER) than in fish fed diets supplemented with biotin. The highestweight gain, SGR, FER and PER were noticed in fish fed 1 mg biotinkg^–1, followed by 0.5, 5, 3 and 0.1 mg biotinkg^–1, except for PER (followed by 0.5, 5, 0.1 and 3 mgbiotin kg^–1). Quadratic analysis showed that the optimumdietary biotin requirements for maximal weight gain, PER and PER were2.49, 2.54 and 2.52 mg kg^–1, respectively. Liver biotinconcentrations were influenced by levels of biotin in the diet.Concentration of liver biotin increased as level of dietarysupplementation increased and no biotin was detected in the liver of thecontrol fish. Liver pyruvate carboxylase and acetyl CoA carboxylaseactivities were higher in fish fed biotin-supplemented diets than incontrols. Biotin concentrations, pyruvate carboxylase and acetyl CoAcarboxylase activities in liver associated with normal growth rangedfrom 10.59 to 10.66 g g^–1, 147.97 to 148.18 units mgprotein^–1 and 12.76 to 12.78 units mg protein^–1, respectively. Biotin deficiency symptoms such as anorexia, darkskin colour and convulsions were observed in fish fed the control diet.The optimum dietary biotin requirement for maximal growth of C.batrachus is about 2.49 mg kg^–1 diet.     

Rates of oxygen consumption and ammonia excretion of juvenile Eurasian perch Perca fluviatilis L.

The impact of feeding, fish size (body weight from 18.5 to 56.5 g) and water temperature (20 and 23 °C) on oxygen consumption (OC, mg O₂ kg^–1 h^–1) and ammonia excretion (AE, mg TAN kg^–1 h^–1) was studied in Eurasian perch held in recirculation systems. OC for both fed and feed-deprived (3 days) fish was higher at 23 °C (278.5 and 150.1 mg O₂ kg^–1 h^–1) than at 20 °C (249.3 and 135.0 mg O₂ kg^–1 h^–1; P < 0.01). AEs for both fed and feed-deprived fish were also significantly higher at 23 °C than at 20 °C (P < 0.001). Water temperature and fish size had a significant impact on the oxygen:feed ratio (OFR, kg O₂ kg^–1 feed fed day^–1) and ammonia:feed ratio (AFR, kg TAN kg^–1 feed fed day^–1; P < 0.001). Their average values at temperatures of 20 and 23 °C were 0.17 and 0.19 kg O₂ kg^–1 feed fed day^–1 and 0.009 and 0.011 kg TAN kg^–1 feed fed day^–1, respectively.     

Suitability of European green frogs for intensive culture: Comparison between different phenotypes of the esculenta hybridogenetic complex

European countries are probably the greatest consumers of frogs' legs, although this is occurring in a context of amphibian decline. Imports of frogs' legs have been increasing over the last few decades in relation to the development of deep-frozen products. This demand has stimulated farming with neotropical species for international trade. Today, in spite of some trials on European species, no production is effective. From the early 1990s, small-scale experimental rearing trials have been undertaken in Brittany (France) with a local green frog belonging to the esculenta complex (Rana ridibunda) which accepts granulated feed. This complex comprises two Mendelian species R. lessonae (LL) and R. ridibunda (RR) as well as their hybridogenetic hybrid Rana esculenta, which can be either diploid (RL) or triploid (RLL, RRL).The purpose of this study is to analyse the ability of each taxon to be reared. During the two months following metamorphosis, froglets were trained to eat pellets. The surviving individuals were reared for one year under regulated conditions to estimate the survival rate, growth and production of each frog type.The results show low survival rates (14.8 to 26.2%) for LL and RLL, higher rates (39–46.4%) for F₁ and F₂ from wild RR and RLL, with the highest rates (63.0 to 77.4%) for RL, RRL and all RR, using data from several years of rearing. After three years under rearing conditions, the adult survival rate is highest for rearing strain RR-Rivan 92* (53.7%). The growth rate varies greatly according to phenotype, and only frogs with an RR phenotype reach marketable size. In the wild, LL exhibits some difficulty in reaching this limit. As a result, production increases from 1.5–8.7 kg/m² for individuals with an L hemiclone to 22.9–35.7 kg/m² for each cohort of phenotype RR from at least two generations under rearing conditions.In relation to hybridogenesis processes, hybrids with diploid or triploid genomes do not seem to offer any advantage for production purposes. However, R. lessonae individuals from intensive rearing can produce fertile eggs and tadpoles, which could enable production for restocking to preserve wild diversity or build up new populations in suitable habitats.     

Gastric evacuation and feeding in the gilthead sea bream reared under semi-intensive conditions

Gastric evacuation rates of the gilthead sea bream, Sparus aurata, fed with commercial pelleted food and polychaetes (Nereis diversicolor) were determined under experimental conditions. The estimated gastric evacuation rate for pelleted food was 7.97% h^–1, with a total time of digestion of approximately 9 h. The respective values for the natural food were 6.24% h^–1, with a total digestion time of approximately 12 h. The daily consumption of fish reared in earth ponds in a semi-intensive aquaculture facility was estimated through 24 h cycles performed between April and August. The daily consumption varied from 18.58 to 31.98 mg g^–1. There was a constant increase in the average daily consumption per individual of 1.8–4.6 g (dry weight). During these cycles, samples of stomachs were taken and the contents preserved for further observation. The feeding behaviour of the reared fish was compared with a fish sample caught in the Ria Formosa lagoon. No common species were found between samples. A total of 38 prey were identified, which suggests that the gilthead sea bream is a non-specific predator. Despite the high abundance of natural prey in the ponds, the dependence of sea bream on pelleted food was high.