Satiation Feeding Research Articles

Nutritional physiology of mahi-mahi (Coryphaena hippurus): Postprandial metabolic response to different diets and metabolic impacts on swim performance

Migratory pelagic fish species, such as the mahi-mahi (Coryphaena hippurus), must balance numerous metabolic demands simultaneously in order to survive in a challenging oceanic environment. Energetic support for such demands comes from a variety of natural prey items in the wild and can come from manufactured pelletized feed in captivity. This study quantified postprandial metabolism, commonly referred to as specific dynamic action (SDA), over time in adult mahi-mahi (706±25g; 38±0.7cm FL) in response to satiation feeding using three different natural and manufactured diets. Results indicate that during satiation feeding the amount of food ingested is dictated by energy content rather than prey mass, regardless of moisture content of the diet. Ingested meal energy did not differ significantly across groups (473±45kJ), nor did the duration of SDA (36±2.1h). Satiation feeding levels ranged from 2.9–16.2% bodyweight depending on the diet. Peak SDA and SDA magnitude were both significantly decreased in response to dry pelletized diet compared to the natural forage diets, despite equivalent energy consumption. Swim performance and maximum metabolic rate were not impacted significantly in satiation fed fish compared to unfed fish, supporting the evidence that mahi-mahi are able to maintain multiple metabolic demands at one time without compromising performance.

Effects of feeding rates on growth, feed utilization, and body composition of juvenile Pseudobagrus ussuriensis

An 8-week feeding trial was conducted to investigate the effects of feeding rates on growth, feed utilization, and body composition of juvenile Pseudobagrus ussuriensis. Juvenile P. ussuriensis (initial body weight of 2.30 ± 0.01 g) were distributed into 15 tanks, and each tank was stocked with 30 fish. Satiation feeding (3.57% BW day−1) was determined by the point of cessation of voluntary feeding activity by fish. Five treatments that included triplicate groups were prepared for this study: 100% (satiation), 75, 50, and 25% of satiation groups and unfed group. The results indicated that weight gain (WG) and specific growth rate (SGR) increased with increasing feeding rates. WG and SGR of fish fed to satiation were significantly higher than that of fish fed to 50 and 25% of satiation and unfed fish (P 0.05). Feed efficiency (FE) and protein efficiency ratio (PER) of fish fed to 75% of satiation were significantly higher than that of fish fed other groups. There was a trend towards increased whole-body crude lipid and decreased whole-body moisture with increasing feeding rates, while whole-body protein content was not significantly affected by feeding rates. Condition factor and hepatosomatic index were increased with increasing feeding rates (P < 0.05), while there was no significant difference in viscerosomatic index with increasing feeding rates. Considering these experimental results, it can be concluded that the optimum feeding rate for growth of juvenile P. ussuriensis could be lowered to 75% of satiation without growth suppression.

Feeding frequency and feeding regime in catfish: Effects on nutrient utilization, growth, biochemical and haematological parameters

This study investigated growth, nutrient utilization, biochemical and haematological parameters of catfish fingerlings under varying feeding frequencies and regimes. Eight fish were put under different treatments; T (1-8) in triplicates. Fish were bulk weighed at the beginning of the experiment and on a weekly basis for 10 weeks. Significant effects (p&lt;0.05) were recorded in mean weight gain (MWG), specific growth rate (SGR) and feed conversion ratio (FCR) across treatments. The control (T1) had the highest MWG (202.92?4.68) and SGR (4.24?0.05) while the lowest values were recorded in T4 (82.60?15.63 and 3.05?0.23 respectively). The best value for FCR was recorded in T6 (0.20?0.02), which differed significantly (p&lt;0.05) from other treatments except T2. Significant differences (P&lt;0.05) were shown in haemoglobin (Hb) and erythrocyte sedimentation rate (ESR). The highest value for Hb was recorded in T6 (10.8?0.3) and the lowest value in T8 (7.6?0.3). The utmost value for ESR was recorded in T8 (43.5?2.1) while the least value was observed in T6 (19.0?4.2) and no significant differences (P&gt;0.05) were recorded in both PCV and WBC. The blood protein, albumin, creatine, urea, cholesterol, triglyceride and high density lipoprotein did not show significant differences (P&gt;0.05) across treatments. Aspartate aminotransferase and alanine aminotransferase did not show significant differences (P&gt;0.05) in values, while there was a reduction in values of chloride, potassium and sodium with a decrease in the number of feeding days. Results from this study confirmed that satiation feeding, two to three times daily, would enhance growth indices in C. gariepinus fingerlings.

사육 수온 및 사료 공급율이 넙치의 성장 및 체조성에 미치는 영향

A 3×2 factorial experiment was conducted to investigate effects of water temperature and feeding rate on growth and body composition of olive flounder. Triplicate groups of fish (initial body weight of 118 g) fed a extruded pellet (55% protein and 4708 ㎈/g) to satiation and at restricted feeding rates of 0.25 and 0.4% body weight per day (BW/d) at the different water temperatures (13 and 18℃) for 9 weeks. Weight gain increased significantly with increase in feeding rates at each temperature. Weight gain of fish fed to satiation was significantly higher at 18 than 13℃, whereas, that of fish fed at 0.25 and 0.4% BW/d were significantly or slightly lower at 18 than 13℃. Feed efficiency and protein efficiency ratio of fish fed to satiation were not significantly different between 13 and 18℃, but those of fish fed at 0.25 and 0.4% BW/d were significantly higher at 13 than 18℃. The major finding of this study is that satiation feeding is efficient for optimal growth and feed efficiency of grower oliver flounder (116-164 g) in suboptimal water temperatures. The maintenance feeding ration which is zero growth performance, were 0.30 and 0.41% BW/day at 13 and 18℃, respectively. In the restricted feeding regime, compromised growth of fish were worsen in higher water temperature (18℃ vs. 13℃). It might be related to high metabolic rate of fish that spend more energy for maintenance metabolism. Based on these results, we suggest that a satiation feeding regime is recommended for a productive growth of grower olive flounder in the suboptimal temperature.

RNAseq analysis of fast skeletal muscle in restriction-fed transgenic coho salmon (Oncorhynchus kisutch): an experimental model uncoupling the growth hormone and nutritional signals regulating growth.

BackgroundCoho salmon (Oncorhynchus kisutch) transgenic for growth hormone (Gh) express Gh in multiple tissues which results in increased appetite and continuous high growth with satiation feeding. Restricting Gh-transgenics to the same lower ration (TR) as wild-type fish (WT) results in similar growth, but with the recruitment of fewer, larger diameter, muscle skeletal fibres to reach a given body size. In order to better understand the genetic mechanisms behind these different patterns of muscle growth and to investigate how the decoupling of Gh and nutritional signals affects gene regulation we used RNA-seq to compare the fast skeletal muscle transcriptome in TR and WT coho salmon.ResultsIllumina sequencing of individually barcoded libraries from 6 WT and 6 TR coho salmon yielded 704,550,985 paired end reads which were used to construct 323,115 contigs containing 19,093 unique genes of which >10,000 contained >90 % of the coding sequence. Transcripts coding for 31 genes required for myoblast fusion were identified with 22 significantly downregulated in TR relative to WT fish, including 10 (vaspa, cdh15, graf1, crk, crkl, dock1, trio, plekho1a, cdc42a and dock5) associated with signaling through the cell surface protein cadherin. Nineteen out of 44 (43 %) translation initiation factors and 14 of 47 (30 %) protein chaperones were upregulated in TR relative to WT fish.ConclusionsTR coho salmon showed increased growth hormone transcripts and gene expression associated with protein synthesis and folding than WT fish even though net rates of protein accretion were similar. The uncoupling of Gh and amino acid signals likely results in additional costs of transcription associated with protein turnover in TR fish. The predicted reduction in the ionic costs of homeostasis in TR fish associated with increased fibre size were shown to involve multiple pathways regulating myotube fusion, particularly cadherin signaling.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1782-z) contains supplementary material, which is available to authorized users.

Optimal numbers of matings: the conditional balance between benefits and costs of mating for females of a nuptial gift‐giving spider

In species where females gain a nutritious nuptial gift during mating, the balance between benefits and costs of mating may depend on access to food. This means that there is not one optimal number of matings for the female but a range of optimal mating numbers. With increasing food availability, the optimal number of matings for a female should vary from the number necessary only for fertilization of her eggs to the number needed also for producing these eggs. In three experimental series, the average number of matings for females of the nuptial gift-giving spider Pisaura mirabilis before egg sac construction varied from 2 to 16 with food-limited females generally accepting more matings than well-fed females. Minimal level of optimal mating number for females at satiation feeding conditions was predicted to be 2-3; in an experimental test, the median number was 2 (range 0-4). Multiple mating gave benefits in terms of increased fecundity and increased egg hatching success up to the third mating, and it had costs in terms of reduced fecundity, reduced egg hatching success after the third mating, and lower offspring size. The level of polyandry seems to vary with the female optimum, regulated by a satiation-dependent resistance to mating, potentially leaving satiated females in lifelong virginity.

Compensatory growth responses to food restriction in the Chinese three-keeled pond turtle, Chinemys reevesii.

Juvenile Chinese three-keeled pond turtles (Chinemys reevesii) were subjected to one of four different feeding regimens: ad libitum (AL), restricted (R), ad libitum-restricted (AL-R), or restricted-ad libitum (R-AL) for 13 weeks, to assess the compensatory growth (CG) response to food restriction and subsequent re-alimentation. After switching to ad libitum feeding, the turtles in R-AL group ate more food and grew faster than those in other groups. At the end of the trial, R-AL turtles achieved the comparable body weight as AL turtles, indicating that a complete CG response occurred. Cumulative food consumption over the entire period did not differ between R-AL turtles and AL turtles. Experimental treatment affected carcass composition. Carcass lipid content of AL turtles was greater than that of R and AL-R turtles, with R-AL turtles in between. Carcass protein content of R-AL turtles was slightly greater than that of other groups without statistical differences. Stored lipids might be consumed firstly when animals underwent food restriction. Our results reconfirmed the CG of C. reevesii after food restriction. However, it is still difficult to achieve a reduction in the cost of farm-raised turtle production by adopting a restricted–satiation feeding protocol.

Ration restriction, compensatory growth and pituitary growth hormone gene expression in Labeo rohita

An experiment to investigate the compensatory growth (CG) response of Labeo rohita was conducted in two phases: a first phase (6 weeks) in which triplicate groups of fish were subjected to feed restriction (5, 25, 50 and 75 % of satiation) or satiation feeding (control) and a second phase (6 weeks) of satiation feeding for all treatment groups. CG in body weight occurred in groups which were under moderate feed restriction (50–75 % of satiation) under phase 1, but more severe feed restrictions resulted in lower weight gain. Improved feed conversion ratio (FCR) (1.6 ± 0.05 and 1.9 ± 0.03) relative to control (2.1 ± 0.06) was observed in the fish that displayed CG following moderate feed restriction (50–75 % of satiation). At the end of the experiment, body moisture, lipid and protein content were not significantly different between moderately restricted fish and the control. After the first phase, there was no significant difference in the expression of pituitary growth hormone (GH) gene between groups, but at the end of the experiment, significantly lower GH expression was observed in the fish subjected to a restriction of 25 and 50 % of satiation during phase 1. Exploiting the ability of fishes to undergo CG in terms of weight gain and improved FCR without major changes in body composition can be considered as an effective management practice.

Optimization of Phosphorus Fertilizer in Supplemental Feed-Fed Based Nile Tilapia (Oreochromis niloticus) Ponds

An experiment was conducted in earthen ponds at the Asian Institute of Technology, Thailand to determine different phosphorus fertilizer dose effects on Nile tilapia production, water quality variables, nutrient utilization and cost-benefit under supplemental feeding. Five phosphorus fertilization rates were used as treatments e.g. 100%, 75%, 50%, 25% and 0% of 7 kg P ha week−1. Nitrogen fertilization rate was fixed at 28 kg N ha week−1 for all the treatments. Sex-reversed Nile tilapia were stocked at 3 fish m−2, and 30% CP floating feed fed at 50% satiation feeding rate. Nutrient budget showed higher phosphorus fertilizer input resulted in higher phosphorus sink in the sediment. Mean weight, mean weight gain, daily weight gain and net yield were not significantly different among treatments (P > 0.05). Total Kjeldahl nitrogen, total phosphorus and soluble reactive phosphorus were significantly different among treatments. Economic analysis showed phosphorus fertilization resulted in positive net returns. Though the gross income was not affected by different fertilization rates, significantly lowest cost was found in the treatment using 25% phosphorus fertilizer. It can be concluded from the research that 25% phosphorus fertilization might be used as an alternative strategy of Nile tilapia pond culture in terms of economic return and nutrient loss in sediment.

Overcompensation of circulating and local insulin-like growth factor-1 during catch-up growth in hybrid striped bass ( Morone chrysops × Morone saxatilis ) following temperature and feeding manipulations

Abstract Teleosts and other aquatic ectotherms have the ability to withstand prolonged periods of low water temperatures (cold-acclimation) and fasting, and can often respond with phases of accelerated (compensatory) growth when favorable conditions are restored. We assessed whether complete feed restriction prior to (24 °C, days 0–23) and/or during (14 °C, days 24–114) a simulated period of cold-acclimation could elicit episodes of compensatory growth (CG) and catch-up growth upon warm-up to 24 °C and satiation feeding (days 115–148). Control hybrid striped bass (HSB: Morone chrysops × Morone saxatilis ) were fed to satiation throughout the entire experiment under these temperature fluctuations. Compensatory growth and ultimately catch-up growth were achieved in groups of HSB that were deprived of feed during either the initial period at 24 °C (days 0–23), during the cold-acclimation period (14 °C, days 24–114), or during both of these periods (days 0–114). Further, it appears that HSB are better able to compensate for weight loss when skeletal length is not significantly compromised during the treatment period, which occurred in HSB feed restricted during cold-acclimation only. The most dramatic CG responses were defined by specific growth rates (SGRs) up to 4.2 times that of controls and were accompanied by hyperphagia and improvements in temporal and overall feed conversion. Levels of plasma insulin-like growth factor (IGF)-1 and muscle IGF-1 mRNA were significantly correlated to growth rate for all groups throughout the experiment (R 2 = 0.40, 0.23, respectively), with an overcompensation of both observed in HSB with the most elevated SGRs during the CG response. Interestingly, opposing trends were observed between muscle mRNA expression of growth hormone receptor (GHR)-1 and -2, with fasting at 24 °C and 14 °C resulting in depressed levels of GHR-1 and elevated levels of GHR-2 relative to controls. Levels of muscle myostatin (MSTN)-1 mRNA were significantly depressed in HSB fasted at 24 °C and/or 14 °C while MSTN-2 mRNA was lower following initial feed restriction at 24 °C. Likewise, levels of unprocessed pro-MSTN (precursor) and mature MSTN protein were both depressed in fasted fish at 24 °C. This study demonstrates that a previous period of feed restriction and cold-acclimation followed by realimentation at more favorable water temperatures produces a strong CG response and catch-up growth in fish. These studies also suggest that an overcompensation of circulating and local IGF-1 along with changes in MSTN mRNA and protein expression may contribute to accelerated growth rates characteristic of CG. Furthermore, our studies indicate that overall feed conversion can improve by as much as 30% with CG induced through temperature and feeding manipulations with no adverse effects on growth of HSB. This raises the possibility that CG protocols can improve production efficiency of HSB and other temperate teleosts in pond or tank culture.

Effects of Dietary Nutrient Composition on Compensatory Growth of Juvenile Blunt Snout Bream Megalobrama amblycephala

AbstractA feeding trial was conducted to evaluate the influences of dietary nutrient composition on the compensatory growth of Blunt Snout Bream Megalobrama amblycephala. Three diets were tested: a control, a high‐protein (HP), and a high‐protein and carbohydrate (HPC) diet. Each of the three diets was fed to Blunt Snout Bream (initially weight, 24 ± 0.50 g) for 60 d using either satiation feeding (in which fish were fed daily) or restricted feeding (no feeding for 3 d followed by feeding for the next 12 d). The weight gain of fish fed the HP and HPC diets was significantly higher than that of fish fed the control diet. In addition, restricted feeding led to significantly less weight gain than daily feeding with the control and HP diets. However, there was no significant difference between the two feeding regimes in the weight gain of fish fed the HPC diet. The feed conversion ratio of fish fed the control diet was significantly higher than that of fish fed the HP and HPC diets. Moreover, the ratio was significantly lower with restricted feeding than with satiation feeding. Whole‐body composition was not significantly different among treatments. Fish subjected to the restricted feeding regime had an elevated hepatosomatic index compared with fish fed to satiation. On the whole, the HPC diet could improve the compensatory growth of fish without altering their whole‐body composition, and compensatory growth has the advantage of improving feed efficiency and nutrient retention.

Effect of short-term cyclic feed deprivation on growth and economic limit of commercial feed-based in-door grow-out of Clarias gariepinus (Burchell, 1822)

Growth, feed utilization, and economic limit of commercial pelleted feed use were compared between daily-fed and feed deprived groups of Clarias gariepinus (Burchell, 1822) raised under low density culture. Groups of C. gariepinus were fed daily (Treatment 1) or on alternate days (Treatment 2) for 5½ months, with 45% crude protein commercial pellets. Feeding was at a rate of 6% body weight per day which was considered satiation feeding. Cost and revenue were determined on the basis of feed cost and revenue from fish sales respectively. Treatment 1 yielded profits up to a mean weight of 64±8 g at feed conversion ratio 1.0±0.08 and 4.71% loss at mean weight of 105±10 g and feed conversion ratio (FCR) 2.1±0.7. Treatment 2 was profitable up to harvest mean weight of 264±10 g. Feed conversion ratio, mean weight, and total weight, were significantly higher in Treatment 1 (p<0.05). Cost-benefit ratio and percentage profit were significantly higher in Treatment 2 (p<0.0001). Thus the economic limits were 2 months at mean weight of 105±10 g; and 5 months at mean weight 264±10 g; in Treatments 1 and 2 respectively. The skip-a-day feeding strategy adopted in Treatment 2 was effective in extending the economic limit of conventional feeding using commercial pelleted feed in low density commercial catfish culture. The limits established in this study could serve as an advisory to farmers on the appropriate time to switch from the expensive commercial pelleted feeds usually fed at the early stage of grow-out to farm-made feeds. Key words: Clarias gariepinus, economic limit, low density, feed deprivation, satiation feeding, growth, feed utilization.

Increasing growth and feed efficiency of Juvenile Walleye,Sander vitreus(Mitchill, 1818), through novel, subsatiation, restrict/feed cycles from late summer into fall

The role of restricted feeding on the growth and feed efficiency (FE) of juvenile walleye, Sander vitreus, was investigated through two experiments. In the summer/fall experiment, 7.44-g walleye were fed on one of the three schedules for 84 days: control (daily satiation feeding at 6% BW day−1), D2 (2 days of feed deprivation, then fed at 12% BW day−1 for 7 days, repeated throughout the study) and SS80 (subsatiation feeding involving 2 weeks of maintenance ration, then fed at 80% of the control group's feeding level). Juvenile walleye growth rates were significantly higher in the SS80 than in the control group, however, their growth rates in the D2 group were no different than in the control. Mean FE of the SS80 group (0.49), significantly exceeded those of the control (0.36) and D2 (0.28) groups. In contrast with the summer/fall experiment, no differences in growth rate were detected among the control, SS80 and D2 groups in the subsequent 84-d spring experiment, where the juvenile walleye (97.45 g) were substantially larger, and their mean FE values were generally lower, with less distinction observed among the groups. Our findings indicate potential to increase growth and FE of juvenile walleye in advance of fall, by applying restrict-feed schedules.

Expression of Heat Shock Protein (Hsp90) Paralogues Is Regulated by Amino Acids in Skeletal Muscle of Atlantic Salmon

Heat shock proteins 90 (Hsp90) have an essential role in sarcomere formation and differentiation in skeletal muscle and also act as molecular chaperones during protein folding impacting a wide range of physiological processes. We characterised and provided a phylogenetically consistent nomenclature for the complete repertoire of six Hsp90 paralogues present in duplicated salmonid fish genomes (Hsp90α1a, Hsp90α1b, Hsp90α2a, Hsp90α2b, Hsp90ß1a and Hsp90ß1b). The expression of paralogues in fast skeletal muscle was investigated using in vivo fasting-feeding experiments and primary myogenic cultures. Fasted juvenile Atlantic salmon (Salmo salar) showed a transient 2 to 8-fold increase in the expression of all 4 Hsp90α paralogues within 24h of satiation feeding. Hsp90α1a and hsp90α1b also showed a pronounced secondary increase in expression after 10 days, concomitant with muscle differentiation and the expression of myogenin and sarcomeric proteins (mlc2, myhc). Hsp90ß1b was constitutively expressed whereas Hsp90ß1a expression was downregulated 10-fold between fasted and fed individuals. Hsp90α1a and Hsp90α1b were upregulated 10 to 15-fold concomitant with myotube formation and muscle differentiation in vitro whereas other Hsp90 paralogues showed no change in expression. In cells starved of amino acid (AA) and serum for 72h the addition of AA, but not insulin-like growth factor 1, increased phosphorylation of mTor and expression of all 4 hsp90α paralogues and associated co-chaperones including hsp30, tbcb, pdia4, pdia6, stga and fk504bp1, indicating a general activation of the protein folding response. In contrast, Hsp90ß1a expression in vitro was unresponsive to AA treatment indicating that some other as yet uncharacterised signal(s) regulate its expression in response to altered nutritional state.

Effect of Various Lengths of Single Phase Starvation on Compensatory Growth in Rainbow Trout under Summer Conditions (Oncorhynchus mykiss)

This study was conducted to determine the effects of various lengths of starvation periods on following compensatory growth (CG) in rainbow trout under summer conditions (18.1°C and day length of 12.5-14.5 hours). Five treatments with triplicate tanks were as follows: control (C) fed to satiation over 84 days; one (S1), two (S2), three (S3), and four (S4) weeks of starvation; and then refeeding for the remaining eight weeks of the experiment. Starvation periods induced hyperphagia during refeeding but only S1 and S2 were able to catch up with C. Repeated measures of analysis of variance suggested a convergence in body mass but not in body length (structure). Organo-somatic indices of the starvation groups were significantly reduced at the end of starvation periods and restored to levels of the control fish within the first two weeks of the refeeding period. Broadly speaking, starvation longer than one week significantly reduced apparent digestibility of dry matter, lipid, and energy compared with the control group but did not affect protein and ash, and a complete recovery in the digestibility coefficients occurred within two weeks of satiation feeding. There was a linear increase in body moisture and a decrease in lipid and lipid/lean body mass ratio with the severity of starvation periods, but these divergences largely disappeared at the end of refeeding. During the starvation period, the protein synthesis rate (estimated using RNA/DNA ratio in the muscle and liver) reduced but in subsequent refeeding period, it increased in starved fish. The findings of the present experiment suggest that an application of single starvation episodes to elicit CG as a management tool in summer conditions should not be longer than two weeks.

Effects of repetitive periods of fasting and satiation feeding on the growth,body composition,metabolism and energy budget of tongue sole(&lt;I&gt;Cynoglossus semilaevis&lt;/I&gt;)

Effects of repetitive periods of fasting and satiation feeding on the growth,body composition,metabolism and energy budget of tongue sole(&lt;I&gt;Cynoglossus semilaevis&lt;/I&gt;)

Effect of various feeding frequencies on growth performance and previously starved fingerlings and juveniles of African catfish (Clarias gariepinus)

Growth performance in fingerlings and juveniles of African catfish Clarias gariepinus , was examined after various feeding frequencies. Fis h were first fed once, twice, thrice and four times daily over a period of 10 weeks before satiation feeding resumed for 12 weeks. Monthly changes in weight gain, feed intake, nutrient utilization and economy of production were monitored. No significant difference was observed in the feed conversion ratio and voluntary feed intake both at the juvenile and fingerling stages. Fish fed thrice a day record ed the highest mean weight gain but no significant differences were observed across the different feeding frequencies in the juvenile fish. The specific growth rate value o f 0.69 and 0.63%/day was observed for the fingerlings and juveniles had the least val ue in fish that were fed four times a day, while no significant differences were observed in all economic parameters measured for the juveniles across the feeding level s. On the contrary fingerlings fed once were significantly different having the lowest values from those fed with other feeding levels in the investment cost analysis and gross profit. It can be concluded that the fish fed at once a day for a period of 10 weeks , can still catch-up with others fed at higher feeding frequencies when returned to satiati on feeding.

Captive spawning and larval rearing of California yellowtail (Seriola lalandi)

A captive population of California yellowtail (Seriola lalandi) was used to document spawning patterns, including measures of egg production, population fecundity and egg and larval quality from 2007 to 2010. Spawned eggs were also used to document larval development and to develop rearing techniques for aquaculture in the region. Broodstock growth and condition factor were best when feeding rations were maintained at 10–15% body weight week−1 during the warm summer months. A winter ration based on satiation feeding was typically 4% body weight week−1. During the 4-year study period, the only broodstock health issue was an infestation by the parasitic gill fluke Zeuxapta seriolae, which was readily treated. Spawning occurred naturally in the 140 m3 tank when the ambient water temperature reached 16°C and ended when the temperature exceeded 22°C. Egg production reached a maximum in 2010 when 43 spawn events were recorded from a pool of nine females yielding 36.8 million eggs in total. The average female size at this time was 20 kg, which equated to a total annual population fecundity of approximately 226 000 eggs kg−1 female year−1. Larval rearing trials yielded survival rates as high as 5.8% from egg to 50 days post-hatch (dph). Successful larval culture methods included the addition of algae paste for green water culture, rotifers (20 rotifers mL−1) at 2 dph and Artemia (5 Artemia mL−1) at 6 dph. Larvae were transferred from the incubation tank at 10 dph to a shallower tank with 33% greater surface area to accommodate the larvae's strong orientation to surface waters. This research represents the first documentation of successful spawning and larval rearing for S. lalandi in the eastern Pacific.

Independence of net water flux from paracellular permeability in the intestine ofFundulus heteroclitus, a euryhaline teleost

Paracellular permeability and absorptive water flux across the intestine of the euryhaline killifish were investigated using in vitro gut sac preparations from seawater- and freshwater-acclimated animals. The permeability of polyethylene glycol (PEG), a well-established paracellular probe, was measured using trace amounts of radiolabelled oligomers of three different molecular sizes (PEG-400, PEG-900 and PEG-4000) at various times after satiation feeding. All three PEG molecules were absorbed, with permeability declining as a linear function of increasing hydrodynamic radius. Response patterns were similar in seawater and freshwater preparations, though water absorption and PEG-900 permeability were greater in the latter. Despite up to 4-fold variations in absorptive water flux associated with feeding and fasting (highest at 1-3 h, lowest at 12-24 h and intermediate at 1-2 weeks post-feeding), there were no changes in PEG permeability for any size oligomer. When PEG permeability was measured in the opposite direction (i.e. serosal to mucosal) from net water flux, it was again unchanged. HgCl(2) (10(-3) mol l(-1)), a putative blocker of aquaporins, eliminated absorptive water flux yet increased PEG-4000 permeability by 6- to 8-fold in both freshwater and seawater preparations. Experimentally raising the serosal osmolality by addition of 300 mmol l(-1) mannitol increased the absorptive water flux rate 10-fold, but did not alter PEG permeability. Under these conditions, HgCl(2) reduced absorptive water flux by 60% and again increased PEG permeability by 6- to 8-fold in both freshwater and seawater preparations. Clearly, there was no influence of solvent drag on PEG movement. The putative paracellular blocker 2,4,6-triaminopyrimidine (TAP, 20 mmol l(-1)) had no effect on net water flux or PEG permeability. We conclude that PEG and water move by separate pathways; absorptive water transport probably occurs via a transcellular route in the intestine of Fundulus heteroclitus.

Use of acceleration loggers in aquaculture to determine net-cage use and field metabolic rates in red sea bream Pagrus major

We investigated the usefulness of acceleration loggers in aquaculture by examining net-cage use and metabolic rates in red sea bream, Pagrus major. First, the fish’s metabolic rate (mg O2 kg−1 min−1) was measured with the logger in a swim tunnel at designated water velocities. We found that metabolic rate could be expressed by using a linear regression model of the activity rate index (unitless min−1) derived from acceleration data. Using this equation, the field metabolic rates of three fish in a net cage were monitored and were estimated at 14.1–15.0 kcal kg−1 day−1. The results suggested that 15–19% of energy from satiation feeding ration was consumed for metabolism and activity in the net cage. The loggers showed orderly net-cage use by the fish. Tagged individuals used the whole cage from surface to bottom, but individual fish that preferred the surface area rarely used the bottom, and vice versa. Metabolic rate increased significantly with distance of the fish from their preferred depths. The logger provided information on the physiological and behavioral responses of fish in a given breeding system, and its use should contribute to the design of practical aquaculture systems.