Quantitation of inert feed ingestion in larval silver sea bream (Sparus sarba) using auto-fluorescence of alginate-based microparticulate diets

The ingestion of an inert feed as a sole food source was investigated in larval silver sea bream (Sparus sarba) fed an alginate-based microparticulate diet. Using the auto-fluorescent properties of pigments associated with the alginate base, ingestion and gut content were investigated over a 6 h experimental period in fed and unfed larvae. By extracting and measuring chlorophyll a (Chl a) and phaeopigment content of feeding larval fish and relating this to standardized Chl a and phaeopigment content of the diet, relative to diet weight, it was determined that individual fed 7-day old larvae had a maximum gut content of 1.05±0.09 g diet while 14-day old fed fish had a maximum gut content of 3.17±0.90 g diet. On average, the gut content of 14-day old fish was 2.89 times greater than the gut content of 7-day old fish. The dry weight of larval sea bream increased from 43±4.2 g at day 7 to 134.3±20.4 g at day 14 indicating that growth of fish fed this inert feed was substantial. Gut pigment dynamics suggested that Chl a was degraded to phaeopigments by 7-day but not 14-day old larvae and the individual gut dietary content varied considerably in 14-day old fish. The maximum Chl a and phaeopigment content in larval sea bream was 0.4 ng ind^–1 and 0.55 ng ind^–1 for 7-day old fish and 1.54 ng ind^–1 and 2.81 ng ind^–1 for 14-day old fish respectively. The present method may potentially allow simple and direct assessment of larval fish feed ingestion in both an experimental and commercial setting.     

The effects of experimental anaemia on CO2 excretionin vitro in rainbow trout,Oncorhynchus mykiss

The effects of severe experimental anaemia on red blood cell HCO₃ ^– dehydrationin vitro were examined in rainbow trout,Oncorhynchus mykiss. After 5 days of anaemia (haematocrit=4.9±1.1%) induced by intraperitoneal injection of phenylhydrazine hydrochloride, fish displayed elevated arterial CO₂ tensions (anaemic PaCO₂=3.19±0.42 torrvs. control PaCO₂=1.35±0.17 torr) and a significant acidosis (anaemic pHa=7.73±0.04vs. control pHa=7.99±0.04). However, after 15–20 days of anaemia (hct=6.6±0.8%) induced by blood withdrawal, the arterial CO₂ tension was significantly lower than the control value, suggesting that physiological adjustments occurred within this time period to compensate for the lowered haematocrit. Compensation probably did not involve alterations in ventilation, which was unaffected by 5 days of anaemia (anaemic ;w=786±187 ml min^–1 kg^–1 vs. control ;w=945±175 min^–1 kg^–1), based on indirect Fick principle measurements.Potential adaptations to longer term anaemia at the level of the red blood cells were investigated using a radioisotopic HCO₃ ^– dehydration assay. Owing to the difference in haematocrits, the HCO₃ ^– dehydration rate for blood from anaemic fish was significantly lower than that for control fish following equilibration at the same CO₂ tension. This difference was eliminated when HCO₃ ^– dehydration rates were measured on blood samples adjusted to the same haematocrit, a result which implies that the intrinsic rate of CO₂ excretion at the level of the red blood cell was not up-regulated during anaemia. The difference was also eliminated by equilibrating the blood samples with CO₂ tensions appropriate for the group from which the sample was obtained,i.e., PCO₂=1.4 torr for control samples and PCO₂=3.2 torr for anaemic samples; each at the appropriate haematocrit. It is concluded that the elevated PaCO₂ helps to reset CO₂ excretion to the control level, but that some additional physiological adjustment occurs to lower the PaCO₂ after 15–20 days of anaemia.     

Ionoregulatory and respiratory responses of brown trout,Salmo trutta,exposed to lethal and sublethal aluminium in acidic soft waters

Soft water acclimated (Ca²⁺ 0.02 mM; Na⁺ 0.03 mM; K⁺ 0.01 mM; pH 7.0), cannulated brown trout (Salmo trutta) were exposed to various pH and aluminium (Al) regimes (pH 7.0, pH 5.0, pH 5.0 plus Al: 50, 25, and 12.5 g l^–1) for up to 5 days in order to determine (i) the sublethal concentration of Al at pH 5.0 for this species (ii) their ionoregulatory and respiratory status. No mortality or physiological disturbances were evident at pH 7.0 or pH 5.0. All trout died within 48 h at pH 5.0 in the presence of Al at 50 g l^–1 and 67% died over the 5 day period at pH 5.0 in the presence of Al at 25 g l^–1. Fish at these lethal Al concentrations showed significant decreases in arterial blood oxygen content (C_aO₂) but no changes in plasma osmolarity or the concentrations of plasma Na⁺, K⁺ and Cl^–. Physiological disturbance was more marked at the 50 g l^–1 Al concentration. The surviving fish at 25 g l^–1 showed few signs of physiological recovery while continually exposed to this regime. No fish died during the exposure to water of pH 5.0 containing 12.5 g l^–1 Al, but physiological disturbance was still apparent. These sublethally-stressed trout showed a transient decline in the plasma concentrations of Na⁺ and Cl^–1. Although C_aO₂ decreased, recovery was evident. The data suggest that in the brown trout, environmental Al concentration is as important as pH and calcium concentration in determining the physiological status of the fish.     

The effect of seawater flow and temperature on metamorphosis and postlarval development in great scallop

Variations in growth and survival of hatchery-reared post-metamorphicjuveniles of great scallop Pecten maximus prompted anexamination of settlement and postlarval development. The effects ofseawater flow and temperature on great scallop metamorphosis andpostlarvae were studied over a 4–5 week period. In allexperiments, and regardless of environmental conditions, great scallopmetamorphosed after a 2–3 week period with values of 35 to70%. Subsequently, spat numbers increased slightly. Spatmortality generally occurred from the third week onward and reachedlevels as high as 30% by the fifth week under standardconditions. At 20 °C, however, 60% mortality levels wererecorded. Differences in spat growth rate, ranging from 37 to 45 mday^–1, were noticed at different seawater flow ratesbut no clear tendency could be discerned. Temperature affected spatgrowth with an increase in size from 24 m day^–1 at15 °C to 35 m day^–1 at 18 °C. Conversely,growth was suppressed at 20 °C (14 m day^–1).For optimal metamorphosis and postlarval development in great scallop, aseawater flow of 4.3 L h^–1 per sieve and a temperatureof 15 °C are recommended.     

Brackishwater carp culture in potentially waterlogged areas using animal wastes as pond fertilizers

In order to assess the possibilities of utilizing drainage effluents (salinity range 5.0–12.5), fish culture experiments were carried out. Experiments on polyculture using cow dung (24 000 kg ha^–1 y^–1) as pond fertilizer were conducted at five different salinity levels (0.3–8.5). Studies have revealed that carp perform well in salinities up to 7.5 and reasonably high fish production has been obtained. Even though the ponds had a high trophic status, higher salinities ( > 7.5) appear to repress fish growth probably due to low dissolved oxygen (DO), high BOD and high NH₄-N. Experiments on monoculture of common carp (Cyprinus carpio) conducted at two different salinity levels (0.3–0.9 and 6.0–7.0) using four different organic fertilizers (cow dung at 24 000 kg and 20 000 kg, poultry at 1500 kg, duck at 6000 kg and sheep/goat at 1500 kg ha^–1 y^–1) have revealed the highest fish growth to be in poultry-treated ponds, followed in decreasing order by duck and sheep/goat wastes. Similar trends in fish production were observed both in fresh- and salt-water ponds. However, fish production was lower in ponds having higher salinities ( > 7.5). Nevertheless, these studies indicated that inland saline waters can be utilized for fish culture. With minor modifications in the existing technology of fish culture in stagnant freshwater fish ponds, animal wastes could be used to fertilize brackishwater fish ponds.     

Estradiol-17β suppresses testicular development and stimulates sex reversal in protandrous black porgy,Acanthopagrus schlegeli

Two year old black porgy (Acanthopagrus schlegeli) fed a diet containing 4.0 mg kg^–1 of estradiol-17 (E₂) for 5 months had significantly lower GSI than the control group during the spawning season. E₂ suppressed testicular development, spermiation and plasma testosterone (T) and 11-ketotestosterone (11-KT) and stimulated ovarian development, vitellogenesis and sex reversal. Spermiation in the control group occurred in January and February with the concentrations of 1.08–1.36 × 10¹⁰ sperm ml^–1 of milt. Higher plasma T and 11-KT, but lower E₂ levels were detected in the spermiating fish (control group). Higher plasma E₂ levels were detected in the sex reversing black porgy during the pre-spawning season. A sharp rise in plasma 11-KT and a drop in T levels were detected in spermiating fish (control group) from January to February. Plasma 11-KT levels correlated with the testicular development and spermiation. The data suggest that E₂ plays an important role in controlling the sex reversal of black porgy.to whom correspondence should be addressed.     

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.     

Osmoregulation in the mudskipper,Boleophthalmus boddaerti I. Responses of branchial cation activated and anion stimulated adenosine triphosphatases to changes in salinity

The mudskipperB. boddaerti, was able to survive in waters of intermediate salinities (4–27). Fish submerged in dechlorinated tap water suffered 60% mortality by the fifth day while 60% of those in 100% sea-water (sw) died after the third day of exposure. After being submerged in 50% or 80% sw for 7 days, the plasma osmolality, plasma Na⁺ and Cl^– concentrations and the branchial Na⁺ and K⁺ activated adenosine triphosphatase (Na⁺,K⁺-ATPase) activity were significantly higher than those of fish submerged in 10% sw for the same period. However, the activities of the branchial HCO₃ ^– and Cl^– stimulated adenosine triphosphatase (HCO₃ ^–,Cl^–-ATPase) and carbonic anhydrase of the latter fish were significantly greater than those of the former. Such correlation suggests that Na⁺,K⁺-ATPase is important for hyperosmotic adaptation in this fish while HCO₃ ^–-Cl^–-ATPase and carbonic anhydrase may be involved in hypoosmotic survival.     

Growth and feed utilisation of rainbow trout subjected to changes in feed lipid concentrations

Rainbow trout Oncorhynchus mykiss grew from 44 to 326 g in 96days when held at 12 °C. Fish were fed to satiation twice dailywith either high (L₁: 30.8%, L₂:31.4%) or lower-lipid feeds (C₁: 18.8%,C₂: 21.8%). Four feeding treatments were studied.Group C₁C₂ received feed C₁ for 43 days(days 0–43) and C₂ thereafter (days 44–96).Groups L₁L₂, L₁C₂ andC₁L₂ were subjected to dietary changes asindicated by the feed designations. After a short period of feedadaptation, fish ingested similar amounts of feed energy i.e., they ateless by weight of the lipid-rich (L) feeds. Feed lipid content did notaffect growth but fish fed L-feed had reduced feed conversion ratio(FCR) compared to fish fed C-feed (0.731 vs. 0.773) during days0–43 (P < 0.01). After 96 days,L₁L₂-fish were lower in body protein(15.8%) than the C₁C₂-fish (16.8%)(P < 0.01). L-feeds also tended to increase percentage lipidand reduce percentage whole body moisture and ash. A higher net proteinutilisation (NPU) was recorded in fish fed L-feeds (43.6%)compared to fish fed C-feeds (38.8%) in days 0–43(P < 0.05). This seemed to be the result of a lower proteinintake rather than a protein-sparing effect of feed lipid. Above athreshold value of approximately 6.5 mg protein eaten·g bodywt_{minus 1}·day_–1, NPU decreased.     

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 m 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.     

Effects of dietary carnitine and lipid on growth and body composition of hybrid striped bass (Morone chrysops ♀× M. saxatilis ♂)

A study was undertaken to investigate the effects of graded dietary levels and different types of carnitine on hybrid striped bass (Morone chrysops × M. saxatilis %) fed different levels of lipid. An incomplete factorial design was utilized in which diets containing lipid at either 5 or 10% were supplemented with l-carnitine at 0, 500, or 1000 mg kg^–1 diet, dl-carnitine at 1000 mg kg^–1 diet, or carnitine chloride to provide 1000 mg carnitine kg^–1 diet. Juvenile hybrid striped bass (3.3 g fish^–1) were stocked into individual 38-l aquaria connected as a brackish water (6), recirculating system and fed each diet in triplicate for 9 weeks.Supplementation of the diet with 1000 mg carnitine kg^–1 increased muscle carnitine from 35.5 to 47.7 g g^–1 tissue. Carnitine supplementation did not result in increased weight gain regardless of carnitine level or type; however, weight gain showed a significant (p<0.05) response to dietary lipid with fish fed diets containing 10% lipid growing 34% more than fish fed diets with 5% lipid. The hepatosomatic index also was unaffected by diet, but the intraperitoneal fat (IPF) ratio was significantly elevated (5.1 vs 3.2%) in fish fed diets with 10% lipid compared to those fed diets with 5% lipid. Fish fed diets containing 1000 mg carnitine kg^–1 had increased IPF ratio values at 4.7% compared to 3.9% for fish fed the basal diet. Liver lipid also was responsive to dietary treatment, increasing from 6.7 to 8.8% of wet weight as dietary lipid increased from 5 to 10%. The relative quantities of triglycerides, free fatty acids and phospholipids in muscle and liver were not influenced by carnitine level, carnitine type or dietary lipid level. Supplementation of carnitine does not appear to be beneficial to hybrid striped bass based on either growth performance or body composition.     

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.     

Oxygen consumption and responses to hypoxia of ammocoetes of the southern hemisphere lampreyGeotria australis

The standard rate of oxygen consumption of ammocoetes (larvae) ofGeotria australis with a mean weight of c. 0.5 g was 9.6, 31.4 and 59.4l g^–1 h^–1 at 4.5, 15.5 and 25.0°C respectively, which gives an overall Q₁₀ of 2.4. The regression coefficient for the logarithmic relationship between oxygen consumption and body weight at 15.5°C was 0.704. The ammocoetes ofG. australis have a much lower rate of oxygen consumption at 15.5 and 25.0°C than those of holarctic lampreys. This presumably reflects the lower oxygen delivery pressure to their tissues and helps account for their slow growth rate. At 15.5°C, ammocoetes ofG. australis emerged from the substrate at 21–25 mm Hg and, unlike those of the Northern HemisphereIchthyomyzon greeleyi, died at 14–17 mm Hg. Thus, despite having a thinner water/blood barrier in the gills and blood with a higher oxygen affinity and capacity than holarctic ammocoetes, the larvae ofG. australis cannot survive very low dissolved oxygen tensions. This is apparently related to an inability of larvalG. australis to meet the high oxygen requirements of the respiratory pump at these oxygen tensions. During metamorphosis, oxygen consumption at 15.5°C rose from approximately 27l g^–1 h^–1 at the beginning of transformation to 33.2l g^–1 h^–1 by Stage 3 and then rapidly to 66l g^–1 h^–1 at Stage 6. It remained near this level in Stage 7 and the downstream migrant.     

Dehydration is more effective for the control of embryonic development and larval hatching of Diplectanum aequans (Monogenea, Diplectanidae) than formalin and trichlorphon

Embryonic development and larval hatching of the monogenean Diplectanum aequans, gill parasite of sea bass Dicentrarchus labrax, was studied in relation to different prophylactic treatments. Groups of eggs of D. aequans were submitted to different in vitro treatments: formalin (300 and 100 L L^–1 per 1 hour), Neguvon^® (trichlorphon 0.2 mg L^–1 per 48 hours) and dehydration for 4 and 8 hours. Percentages of hatched larvae, aborted larvae and undeveloped embryos were estimated in comparison with the control group. Results showed that 300 L L^–1 formalin and dehydration treatments were able to reduce larval hatching significantly, while Neguvon^® and 100 L L^–1 formalin treatments had no effect.     

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.     

Gluconeogenesis in trout (Oncorhynchus mykiss) white muscle: purification and characterization of fructose-1,6-bisphosphatase activity in vitro

Studies of the enzyme fructose-1,6-bisphosphatase (FBPase) of rainbow trout (Oncorhynchus mykiss) have been undertaken in order to illuminate aspects of skeletal muscle gluconeogenesis in these animals. Maximal activities in crude homogenates of several organs suggest that the liver possesses the greatest FBPase activity on a unit g^–1 tissue basis but that the white muscle, owing to its bulk, contributes substantially to whole body FBPase activity. Studies of fructose-6-phosphate-1-kinase (PFK) and FBPase in crude homogenates of several organs suggests an important role for intracellular pH in regulating the relative carbon flux through the FBPase/PFK locus in vivo. Furthermore, a three-step purification scheme is described for trout white muscle FBPase by which a stable and homogeneous (by SDS PAGE) enzyme preparation (isoelectric point = 7.2; molecular weight = 37.6 kd) was obtained. Kinetic studies of the purified enzyme were undertaken at 20°C under conditions reflective of "rest" and "exercise/recovery" intramuscular pH in vivo. Affinity for substrate (F-1,6-P₂) was increased (Km = 6.88 versus 2.44 mol 1-^–1 as was enzyme activity when pH was lowered from 7.0 to 6.5. Various inhibitor metabolites are identified including F-2,6-P₂ (mixed-type inhibitor, K_i = 0.201 mol 1^–1, pH 7.0) and AMP (non-competitive inhibitor, K_i = 0.438 mol 1^–1, pH 7.0). Inhibition by F-2,6-P₂ was strongly alleviated by a reduction in pH from 7.0 to 6.5 (I₅₀ increased from 0.14 to 0.32 mol 1^–1). AMP on the other hand was a more potent inhibitor at pH 6.5 but this inhibition was totally reversed under conditions of citrate, NH₄ ⁺ and AMP typical of muscle during recovery from exercise in vivo. In purified white muscle enzyme preparations, FBPase demonstrated maximal activity at pH 6.5 whereas the optimal pH of PFK was 7.0 or greater. Indeed, it appears from these in vitro data that regulation by metabolite levels as well as pH are required for net FBPase flux in vivo. It is concluded, therefore that trout white muscle FBPase demonstrates the potential to play an important enzymatic role in the control of intramuscular gluconeogenesis in these animals. The results are discussed in relation to present knowledge regarding the metabolic responses of trout white muscle to, and its subsequent recovery from, exhaustive exercise.     

Protein content and freezing avoidance properties of the subdermal extracellular matrix and serum of the Antarctic snailfish,Paraliparis devriesi

The Antarctic snailfish, Paraliparis devriesi (Liparididae), occupies an epibenthic habitat at a depth of 500–650 m in the subzero waters of McMurdo Sound, Antarctica. This species has watery (97%) gelatinous subdermal extracellular matrix (SECM) comprising a mean of 33.8% of the body weight, the largest known proportion of any adult fish. The protein concentration of the SECM was found to be 6–7 mg ml^–1 (0.6–0.7% w/v). Separation of the polypeptides of the SECM by SDS-PAGE revealed 11 polypeptides ranging in relative molecular mass (M_r) from 67,000 to 13,000, with other unresolved polypeptides of less than 13,000. The isoelectric points of these proteins ranged from 4.85 to 8.05. Partial N-terminal amino acid sequence data were obtained for four of the major SECM polypeptides. The N-terminal amino acid sequences of three of these were not identical to or homologous with any other known sequences, whereas the N-terminal sequence of one polypeptide (M_r 51,000) was identical to partial sequence from the apolipoprotein A-I precursor of Atlantic salmon (Salmo salar). Although not isolated from either SECM or serum, melting point-freezing point behavior of body fluids suggest that Paraliparis possess modest amounts of a noncolligative antifreeze compound. Since relatively small amounts of antifreeze are present in the serum and even less in the SECM, freezing avoidance results from the combined effects of antifreeze and the elevated osmolality of body fluids. There are no special adaptations to prevent freezing in the superficially located high water content SECM.     

Utilization of carotenoids from various sources by rainbow trout: muscle colour,carotenoid digestibility and retention

Rainbow trout (Oncorhynchus mykiss) with a mean (sd) weight of 120 (2) g were fed diets supplemented with astaxanthin extracted from the yeast Phaffia rhodozyma (OY1 = 50 mg carotenoids kg^–1 feed, OY2 = 100 mg carotenoids kg^–1 feed), astaxanthin (AX = 100 mg astaxanthin kg^–1 feed) and canthaxanthin (CX = 100 mg canthaxanthin kg^–1 feed) for 4 weeks. Muscle analyses at the end of the experiment indicated a significantly higher carotenoid concentration in the AX group, while CX and OY1 groups were similar in spite of the differences in dietary concentration. The measure of total muscle colour difference (E^* _ab) between initial samples and 4 week ones was higher for the AX fish group but showed no significant difference between OY1, OY2, and CX. The hue and the reflectance ratio (R₆₅₀:R₅₁₀) of fish muscle increased in proportion to carotenoid intake. Digestibility (ADC) of yeast astaxanthin in OY1 and OY2 groups was significantly higher than that in the AX group. Canthaxanthin ADC was about one sixth of that of astaxanthin (AX group). Carotenoid retention in the muscle, expressed as a percentage of carotenoid intake, was higher for the AX group than that recorded for OY1 and OY2. According to ADC, carotenoid retention showed a marked lower value for the CX group. Muscle retentions were similar for astaxanthins from both sources.     

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.