Muscle development and body growth in larvae and early post-larvae of shi drum, Umbrina cirrosa L., reared under different larval photoperiod: muscle structural and ultrastructural study

Shi drum specimens were maintained under four different photoperiod regimes: a natural photoperiod regime (16L:8D), constant light (24L), equal durations of light and dark (12L:12D) and a reduced number of daylight hours (6L:18D) from hatching until the end of larval metamorphosis. Specimens were then kept under natural photoperiod conditions until 111 days post-hatching. Muscle and body parameters were studied. During the vitelline phase, there was little muscle growth and no photoperiod effects were reported; however, a monolayer of red muscle and immature white muscle fibres were observed in the myotome. At hatching, external cells (presumptive myogenic cells) were already present on the surface of the red muscle. At the mouth opening, some presumptive myogenic cells appeared between the red and white muscles. At 20 days, new germinal areas were observed in the apical extremes of the myotome. At this stage, the 16L:8D group (followed by the 24L group) had the longest body length, the largest cross-sectional area of white muscle and the largest white muscle fibres. Conversely, white muscle hyperplasia was most pronounced in the 24L group. Metamorphosis was complete at 33 days in the 24L and 12L:12D groups. At this moment, both groups showed numerous myogenic precursors on the surface of the myotome as well as among the adult muscle fibres (mosaic hyperplastic growth). The 16L:8D group completed metamorphosis at 50 days, showing a similar degree of structural maturity in the myotome to that described in the 24L and 12L:12D groups at 33 days. When comparing muscle growth at the end of the larval period, hypertrophy was highest in the 16L:8D group, whereas hyperplasia was higher in the 24L and 16L:8D groups. At 111 days, all groups showed the adult muscle pattern typical of teleosts; however, the cross-sectional area of white muscle, white muscle fibre hyperplasia, body length and body weight were highest in the 24L group, followed by the 12L:12D group; white muscle hypertrophy was similar in all groups. Larval survival was higher under natural photoperiod conditions compared to all the other light regimes.     

Influence of temperature on muscle fibre hyperplasia and hypertrophy in larvae of blackspot seabream,Pagellus bogaraveo

The effects of temperature on Pagellus bogaraveo muscle cellularity were investigated, by morphometry, throughout the endogenous feeding stage, testing two rearing temperatures: 14 and 18 °C. The following parameters were estimated in transversal body sections at post‐opercular and post‐anal body levels: the total cross‐sectional muscle area, the total number of fibres and the mean cross‐sectional fibre area. At hatching, no significant influence of the temperature was observed on the morphometric parameters measured in the white muscle. At mouth opening, an increase in the number of post‐opercular white fibres was promoted by the highest temperature. During embryonic development, the red muscle fibre number in the post‐anal part of the larvae increased with higher temperature, but it appears that the difference was no longer present at mouth opening. An increase in the fibre area and in the total cross‐sectional area of red muscle at the post‐anal level was promoted by a 4 °C increase in the temperature during the vitelline phase. In conclusion, the axial musculature of blackspot seabream embryos/larvae reacted differently to temperature influence according to the body location, strongly supporting the need to look at and account for different body locations when evaluating muscle cellularity in fish, namely in growth/aquaculture‐related studies.     

Efficacy, tissue distribution, and residue depletion of oxytetracycline in WS-RLP infected California red abalone Haliotis rufescens

Oxytetracycline (OTC) was recently demonstrated to be an effective therapeutant for California red abalone (Haliotis rufescens) infected with the agent of withering syndrome (WS), a Rickettsia-like prokaryote (WS-RLP). This study examined the influence of temperature on the efficacy and pharmacokinetics of oral OTC treatments on WS-RLP infected red abalone, H. rufescens. Medication was administered in an artificial diet containing 1.85% active OTC at a rate of 103.4 mg/kg abalone for 10, 20 and 30 days at both 13.4 °C and 17.3 °C. Drug residue concentrations, WS-RLP burden and WS-associated pathological changes within foot muscle and digestive gland were measured 3, 17, 23, 42, 63, 81, 102, 122, and 160 days after OTC treatment. In all samples the highest concentrations of OTC were detected on the first sample day. Furthermore, all sampling periods showed significantly less OTC in foot muscle samples relative to corresponding digestive gland samples (p < 0.001). While drug depuration occurred rapidly from foot muscle, unusually high concentrations and long depuration times were measured within the digestive gland. The pharmacokinetic trends in both the foot muscle and digestive gland at 13.4 °C were adequately described by a one-compartment model, while the digestive gland depuration models within the 17.3 °C treatments conformed to a two-compartment model. At both temperatures treatment duration gave rise to significant differences in OTC accumulation and depletion (p < 0.001). Despite this, terminal elimination rate constants were similar. Estimated half-lives were similar among all treatments for digestive gland (23.8–27.5 d) and all treatments for the foot muscle at 13.4 °C (10.7–13.4 d; calculated only for the 13.4 °C treatments). At both temperatures all three durations of drug treatment led to significant reductions in WS-RLP prevalence, foot muscle atrophy, and mortality. WS-RLP re-challenge trials initiated 44, 88, and 122 days following the 10-day treatment at 17.3 °C showed reduced susceptibility to re-infection for up to 88 days after treatment, suggesting that digestive gland OTC residues confer long-term resistance to pathogen. Atomic absorption spectroscopy conducted on both foot muscle and digestive gland found significantly higher concentrations of iron, zinc, and manganese in the digestive gland, offering an explanation behind the underlying mechanism of OTC retention for extended periods within this tissue.     

Effects of body weight, water temperature and ration size on ammonia excretion by the areolated grouper (Epinephelus areolatus) and mangrove snapper (Lutjanus argentimaculatus)

The effects of body weight, water temperature and ration size on ammonia excretion rates of the areolated grouper Epinephelus areolatus and the mangrove snapper Lutjanus argentimaculatus were investigated. Under given experimental conditions, L. argentimaculatus had a higher weight-specific ammonia excretion rate than E. areolatus. Weight-specific ammonia excretion rates of fasted individuals of both species showed an inverse relationship with body weight (W, g wet wt.), but a positive relationship with water temperature (t, °C). The relationships for total ammonia nitrogen (TAN) were: E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=21.4·exp^0.11t·W^−0.43 (r²=0.919, n=60); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=121.5·exp^0.12t·W^−0.55 (r²=0.931, n=60). Following feeding, the weight-specific ammonia excretion rate of E. areolatus increased, peaked at 2 to 12 h (depending on temperature), and returned to pre-feeding levels within 24 h. A similar pattern was observed for L. argentimaculatus, with a peak of TAN excretion being found 6 to 12 h after feeding. Stepwise multiple regression analysis indicated that weight-specific TAN excretion rates of both species increased with increasing temperature and ration (R, percent body wt. d⁻¹): E. areolatus: TAN (mg N kg⁻¹ d⁻¹)=22.8·t−28.8·R−378.2 (r²=0.832, n=24); L. argentimaculatus: TAN (mg N kg⁻¹ d⁻¹)=22.9·t−25.4·R−216.4 (r²=0.611, n=24). The effect of body weight on weight-specific postprandial TAN excretion was not significant in either species (p>0.05). This study provides empirical data for estimating ammonia excretion of these two species under varying conditions. This has application for culture management.     

Effect of the early temperature on the growth of larvae and postlarvae turbot, <Emphasis Type="Italic">Scophthalmus maximus</Emphasis> L.: muscle structural and ultrastructural study

Turbot specimens were kept at three temperatures (T _s ): warm (W) (21–22 °C), ambient (A) (17–18 °C) and cold (C) (13–14 °C) during the larval and early postlarval stages. At 90 days posthatching (dph), all of them were transferred to ambient T until 190 dph. At 2–3 dph, the specimens showed a monolayer of red muscle and immature white fibres; external or dermomyotome cells (presumptive myogenic cells) were observed on the surface of the red muscle. In the following stages, many myogenic cells and presumptive myogenic precursors were observed within the myotome, presumably derived of the dermomyotome. When comparing the growth at the same age (2, 10, 25, 37 dph), the body length and the muscle growth were positively influenced by the warm T, being the hyperplasia the muscle parameter more significantly influenced. The development rate was also positively correlated with the high T: the beginning of the metamorphosis took place at 15, 23 and 25 dph at W, A and C temperatures, respectively, with the highest body length values at ambient temperature. The metamorphosis finished at 25, 30 and 37 dph at W, A and C temperatures, respectively, with the highest body length values at warm temperature. However, the muscle cellularity was similar in all the groups at the end of the metamorphosis. At 90 and 190 dph, the largest body length was observed at W temperature. However, the muscle cellularity was similar between A and W; the number of fibres was similar in all the groups at 190 dph, which shows the beginning of a compensatory muscle growth in A and C, mainly in A.     

Mortality of yellowtail flounder, Limanda ferruginea (Storer), eggs: effects of temperature and hormone-induced ovulation

Yellowtail flounder, Limanda ferruginea (Storer, 1839), is a highly marketable fish species that used to be a significant groundfish in the northwest Atlantic region. The potential of yellowtail flounder for mass rearing has recently been investigated, but studies into aspects of mortality during early ontogeny are lacking. We investigated the impact of spawning inducement on mortality of eggs from fertilisation until hatch, and the effects of rearing temperature on mortality and hatching time in this multiple batch spawning flounder. An ash-free dry mass (AFDM) technique for determining mortality was employed. This technique reduced rearing tank disturbances and provided quantitative mortality estimates. We found (1) that spontaneously ovulated (SO) mean egg mass (AFDM 24.84±0.73 μg) was significantly higher than mean egg mass from induced ovulation (IO) (AFDM 20.09±0.54 μg); (2) that mortality of SO eggs was lower than IO eggs (p=0.028), (3) that SO eggs reached a relatively constant (maximum) mortality by about day 3 and IO eggs by about day 5; (4) that there was no significant difference in mortality between eggs incubated at 10 °C and those incubated at 4 °C (p=0.320); and (5) that time to 100% hatch took significantly longer for eggs incubated at 4 °C (256.0±73.5 h) than those incubated at 10 °C (77.9±11.6 h) (p=0.003). There was considerable variation in egg mortality among batches and females; nevertheless, general trends indicate that GnRHa-induction of ovulation tends to decrease egg quality. In addition, the AFDM technique was an easily employed and accurate method of determining mortality. We recommend that unless coordination of spawning is important to a particular rearing protocol, induced ovulation should not be employed.     

Muscle fiber types,growth and development in the whole myotome of cultured Pacific bluefin tuna Thunnus orientalis

Following the successful development of Pacific bluefin tuna (PBT) aquaculture, it is of considerable importance to determine the muscle fiber types and their growth patterns for future development. Muscle fiber profiles of dorsal ordinary, lateral ordinary (LO) and dark muscles and their growth patterns in PBT from 3.0 to 54.3 kg body weight were studied. Muscle fibers were histochemically stained for NADH-diaphorase and myosin adenosine triphosphatase activity (mATPase), and immunohistochemically stained with S-58 slow-muscle myosin antibody. All muscle fibers in dorsal and LO muscles showed low NADH-diaphorase activity, and acid-labile (pH 4.0 or 4.3) and alkali-stable mATPase activity. In LO muscle adjacent to dark muscle, three intensities of mATPase activity were observed after acid pre-incubation at pH 4.5 or 5.0, and the activity was related to the muscle fiber diameter. In dark muscle, all small and some large fibers stained intensely for NADH-diaphorase activity, related to their high aerobic metabolism. The high-active fibers with NADH-diaphorase in dark muscle were positive for S-58 antibody. Some large fibers in dark muscle showed intermediate NADH-diaphorase activity and high mATPase activity after alkali pre-incubations. These are fast-twitch oxido-glycolytic fibers in dark muscle and transformed to red muscle fibers with increasing body weight.     

Pectoral fins of <Emphasis Type="Italic">Micropogonias furnieri</Emphasis>: a histochemical and ultrastructural study

The myotomal fibres of the pectoral fins of white croaker (Micropogonias furnieri) have been studied using histochemical techniques and transmission electron microscopy (TEM). Succinic dehydrogenase (SDH) for mitochondria, periodic acid Schiff (PAS) for glycogen, Sudan Black for lipids and myosin-adenosintriphosphatase (mATPase) pre-incubated at alkaline and acid pHs were used to visualize the contraction velocity. Three zones were determined: superficial (SZ), medium (MZ) and deep (DZ). Staining for SDH, PAS and Sudan Black was positive only in the SZ. The level of alkaline mATPase was the highest in fibres from the DZ, intermediate in the MZ and low in the SZ; at an acid pH, the reverse was obtained. Fibres from the SZ were small with large quantities of subsarcolemmal mitochondria, scarce intermyofibrilar mitochondria and a well-developed sarcoplasmic reticulum; the myofibrils displayed a polygonal distribution along the entire length of the fibre. Fibres in the MZ were larger than those in the SZ, the myofibrils were densely packed, mitochondria prevailed under the sarcolemma and the sarcoplasmic reticulum was not abundant. Fibres from the DZ were the largest, with ribbon-shaped myofibrils and scarce mitochondria. The intercellular space was abundant and nervous endings were frequently observed.     

Effects of dietary protein level on muscle cellularity and flesh quality in Atlantic salmon with particular reference to gaping

Growth performance, muscle cellularity and flesh quality were investigated in Atlantic salmon (Salmo salar L.) fed either of two diet ranges [high protein (HP), or low protein (LP)], which differed in digestible protein/digestible energy ratios but were of equivalent digestible energy content (21.4 MJ kg⁻¹ wet weight). Smolts from an early maturing (Lochy) and a late maturing (Mowi) strain were PIT-tagged and reared together in duplicate 5×5×5-m sea cages for each diet. The Lochy and Mowi fish were harvested in May and August, respectively, after 417 and 515 days in seawater. The average body weight of fish in each cage at harvest was in the range 3.8–5.4 kg, with no significant difference between diets. The total cross-sectional area of white muscle and the number and diameter of muscle fibres was determined at the level of the first dorsal fin ray. The distribution of muscle fibre diameters was investigated using nonparametric smoothing and bootstrapping techniques. Diet had no effect on fibre size distribution or fibre number in the Mowi strain, and small but significant effects for the Lochy strain. At harvest, in Lochy salmon of average fork length 69 cm there were around 15% more fibres in fish fed the HP than LP ratio diets. However, the 50th percentile of fibre diameter was 20% greater in fish fed the LP than HP diets, such that the total muscle cross-sectional area was similar. The lipid content (14.1–15.3% wet mass), astaxanthin pigment concentration (7.0–8.5 mg kg⁻¹ wet mass) and colour (RocheSalmoFan™ and Minolta Chromatometer readings) of the flesh were similar for both strains and diets. There was no significant difference in the average muscle fibre density between strains and diet, which varied between 60 and 140 fibres mm⁻² muscle cross-sectional area. Gaping during processing of the fillet was in part related to muscle cellularity. Little or no gaping was observed in any fish with a fibre density in excess of 95 fibres mm⁻² muscle. It was concluded that individual variation in fibre density is important in the development of gaping, but that muscle cellularity and flesh quality are relatively insensitive to the protein to energy ratio in the diet over the range studied.     

Welfare aspects of live chilling and freezing of farmed eel (Anguilla anguilla L.): neurological and behavioural assessment

The overall objective of the study was to evaluate a slaughter method of eels, which consisted of chilling until their body temperature was <5 °C for stunning, and subsequently placing them in cold brine at −18 °C for 15 min for killing. Three distinct experiments and a control were performed.

Firstly, 19 eels with an average live weight of 758±44 g were restrained and equipped with EEG, ECG electrodes and a temperature sensor inside the body. Then, they were placed in the ice water. Indices for the induction of unconsciousness and insensibility were the appearance of theta and delta waves and no response on pain stimuli, which disappeared at a body temperature of 8.0±2.1 °C after 12±5 min in 15 eels. The responses to pain stimuli did not disappear in three eels. Within a confidence level of 95%, the percentage of eels that is not effectively stunned during the procedure in ice water of <5 °C was at least 5%. The heart rate decreased from 24±10 beats/min (n=14) to 7±4 (n=11) and became irregular during cooling down. When placed in the brine water of −18 °C, the EEG showed rapid and extreme depolarisation of the membranes, which started after 27±17 s (n=18). The ECG showed fluttering of the heart in all eels. None of the eels recovered after this procedure.

For 10 eels with an average live weight of 128±27 g, it was observed that the body temperature decreased from 17.1±0.6 to 4.0±0.5 °C in the ice water. After 15 min in the brine water of −16.1±2.2 °C, the body temperature decreased to −3.1±2.3 °C.

Finally, three groups of seven eels and eight single eels were placed in ice water of −0.0±0.1 °C. The observation of unrestrained eels revealed four phases. Animals were (1) swimming around in the water, (2) attempting to escape from the ice water, (3) pressing their nose to the wall or corner while showing clonic muscle cramps, and finally (4) breathing only, while all other muscle activity was totally suppressed. Afterwards, they were transferred to cold brine at −18 °C, and none of the eels recovered.

The eight control eels, which were transferred to water at 18 °C, swam around, except for one that was lying in an S-shape position at the bottom. After 570 and 605 s, two eels tried to escape from the box.

The obtained results show that the eels, which were transferred from water at 18 °C to ice water, might be stressed, a specific behaviour and an irregular heart rate were observed. From an animal welfare point of view, it is therefore not recommended to stun eels by live chilling. Moreover, at least 5% of the eels will not be stunned at a body temperature of <5 °C. Placing eels in brine water of −18 °C is an effective method to kill the eels before slaughter. However, it cannot be recommended to place conscious eels in cold brine water, because it takes more than 27 s before unconsciousness may be induced.     

Effect of the photoperiod on the larval development,body growth and muscle cellularity of shi drum (Umbrina cirrosa L.)

Shi drum (Umbrina cirrosa L.) larvae were maintained under three photoperiod regimes: a natural photoperiod regime (16L:8D), continuous light (24L) and equal durations of light and dark (12L:12D) from the end of the vitelline phase to the end of the metamorphosis. Muscle and body parameters were studied at hatching and at 4, 10, 14, 39 and 55 days post hatching (dph). During the vitelline phase, the total body length growth was scarce, whereas the muscle grew significantly, being the hypertrophy of the main mechanism involved. Both the total body length and the hypertrophy were significantly greater at 16L:8D than in the rest of photoperiod regimes. At 10 and 14 dph, the greatest body length was reached at 16L:8D, followed by the 24L group, showing the 12L:12D group the lowest values. At 14 dph, the hypertrophy and hyperplasia were also higher at 16L:8D than in the rest of groups. At 39 dph, the highest values of body length were reached in both 16L:8D and 12L:12D regimes, this latter group reaching the highest values of hypertrophy, thus showing a compensatory growth when comparing with the previous stages. The end of the metamorphosis took place at 50–55 dph in all the groups, with 2.7–3.1 cm of body length (P > 0.05). At this stage, the transverse area of the white muscle was similar among the groups, but the greatest hypertrophy was reached at 16L:8D, whereas the highest hyperplasia was reached at 24L.     

A method for inducing muscle relaxation in the abalone, Haliotis iris

Four chemical and two non-chemical methods for induction of relaxation in the abalone, Haliotis iris, were tested for prospective use in pearl seeding. Requirements were for rapid onset of relaxation, full extension and softening of the foot and epipodium muscle for at least 10 min, and recovery with minimal stress and no mortality. Nembutal at 1 ml/l was most successful, producing relaxed and soft muscle with good accessibility to operation sites, and no mortality. Benzocaine and MS-222 made animals release from container walls within 30–60 min, but the animal's muscle was hard and contracted. Propylene phenoxytol caused muscle contraction and mortality at 2.5 ml/l. The effects of the chemical relaxants were similar in warm (21–22.5°C) and cool (15–16°C) water. Elevation of the water temperature from 18°C to 23°C (without chemicals) caused some softening of the muscle, but was much less effective than Nembutal. Air exposure for up to 4 h was ineffective. This work provides a simple method to relax live abalone for pearl nucleation or other manipulations.     

The effects of temperature and diet on the survival, growth and food uptake of aquarium-held postpueruli of the rock lobster Jasus lalandii

Aquaculture of the rock lobster Jasus lalandii has been considered, but is hindered by a paucity of knowledge about conditions that promote yields. This study investigated the influences of temperature and diet on the growth of aquarium-held postpueruli of J. lalandii. First, postpueruli (11.5±0.2 mm CL) were exposed to temperatures spanning 12–24 °C for a total time period of 77 days, while being given a constant diet of mussel flesh. Under these conditions, intermoult period (IMP) was longest at 12 °C (50.6±1.2 days) and at 24 °C (>57 days), and shortest at 18 °C (35.5±1.1 days). Growth increments (GI) were large at 12–18 °C, smaller at 21 °C and negative at 24 °C. Survival was 100% at 12–16 °C, above which mortalities rose to 70% at 24 °C. Food consumption, body mass and condition all peaked at 18 °C. Thus, growth was optimal at 18 °C, but survival greatest at 12–16 °C.

Second, diet-controlled experiments examined the effects of three different diets (blue mussel, commercial shrimpfeed or an alternation of the two) on survival, growth (IMP and GI) and food uptake of postpueruli (11.0±0.3 mm CL) held at 18 °C for a total time period of 77 days. Feeding rate, average growth, body mass and condition were all highest on the mussel diet, and lowest on the shrimpfeed, and the postpueruli consumed more mussel flesh than shrimpfeed. There was little difference in survival of postpueruli subjected to the three diet treatments.

A diet of exclusively blue mussel yielded higher growth, body mass, condition and food uptake than a diet of either shrimpfeed alone or an alternation of mussel and shrimpfeed. The postpueruli acclimated well to culture conditions and survived on a diet of artificial pellets, thus showing good potential for mariculture. On the present evidence, greatest returns are likely at 16–18 °C and with a diet of mussel flesh.     

Age, growth, and reproduction of silky sharks, Carcharhinus falciformis, in northeastern Taiwan waters

To examine the age, growth and reproduction of silky sharks, Carcharhinus falciformis, in the waters off northeastern Taiwan, 469 specimens (213 females and 256 males) were collected from August 2000 to January 2002 at the Nanfanao fish market, northeastern Taiwan. The relationship between body weight (W) and total length (TL) for both sexes combined was expressed as: W = 2.92 × 10⁻⁶ TL^3.15 (n = 469, p < 0.01). The relationship between TL and vertebral centrum radius (R) for both sexes combined data was estimated as: TL = 25.979 + 18.197R (n = 250, p < 0.01). Growth bands (including translucent and opaque zones) in precaudal vertebrae formed once a year between December and January and were counted up to 11 and 14 for females and males, respectively. The von Bertalanffy growth function (VBGF) was used to model the observed length at age data. The sexes combined VBGF predicted an asymptotic length (L_∞) = 332.0 cm TL, growth coefficient (k) = 0.0838 year⁻¹, age at zero length (t₀) = −2.761 year (n = 250, p < 0.01). Size at 50% maturity for males was estimated to be 212.5 cm based on the logistic curve, which corresponded to 9.3 years. Females matured at 210–220 cm, which correspond to 9.2–10.2 years. The length at birth was estimated to be 63.5–75.5 cm TL. The number of embryos per litter was 8–10 and sex ratio of embryos was 1:1.     

Effect of increased dietary protein level in meagre (Argyrosomus regius) juvenile growth and muscle cellularity

In this study, two different dietary protein levels were tested (500 and 600 g/kg) in meagre juveniles of approximately 2 g, to determine whether a higher body protein diet would favour muscle growth. Results showed that meagre survival and growth were not affected by different levels of dietary protein. However, a higher content of protein was observed in the body composition of meagre fed the P60 diet (656 g/kg versus 624 g/kg). When fish were 82 days after hatched (DAH), protein retention efficiency was significantly higher in fish that were fed the P50 diet (37.1% versus 32.5%). Muscle cellularity changed considerably from the beginning to the end of the trial. The contribution of fibre hyperplasia to muscle growth was reduced although still accounted for 30% in 96 DAH meagre. Several differences were found in the frequency of fibres with areas between 1,000 μm² and 2,200 μm² between younger and older meagre, but no effect was found associated with dietary protein. This study suggests that neither growth nor muscle cellularity of fast‐growing juvenile meagre is positively affected by an increased dietary protein levels.     

Effects of light spectrum on growth and physiological status of gilthead seabream Sparus aurata and rainbow trout Oncorhynchus mykiss reared under recirculating system conditions

Previously reported data clearly indicate that depending on species, ambient light spectrum can affect fish growth, physiology, behaviour, reproduction, etc. Since light spectrum can be easily controlled in intensive indoor fish farming facilities, the present study aimed to investigate the effects of coloured light on growth performance (body weight, growth rate, food utilization, carcass composition, etc.) and physiological status (blood and plasma parameters, brain neurotransmitters, tissue fatty acid composition, etc.) of two widely reared fish species, gilthead seabream Sparus aurata and rainbow trout Oncorhynchus mykiss. For this purpose, 240 specimens of S. aurata (29.8 ± 0.13 g) and 60 specimens of O. mykiss (71.4 ± 0.30 g) were exposed to white (full-spectrum, fluorescent lamps), red (605 nm) and blue (480 nm) light (lamps covered with appropriate filters) for 11 weeks under recirculating water systems. Blue light had a significantly negative impact on O. mykiss growth performance accompanied with reduced liver total lipids and plasma glucose and increased brain serotonergic and dopaminergic activity. In the case of S. aurata, red light significantly increased brain dopaminergic activity, while a tendency towards reduced growth was also observed. Since these results indicated the establishment of stressful conditions, O. mykiss and S. aurata should not be reared under blue and red light, respectively. For each species, the effect of the remaining light colours tested, was not clearly differentiated so that an appropriate light spectrum for the most efficient farming of O. mykiss and S. aurata could not be suggested, at least for the time period examined. Nevertheless, present results suggest that light colour should be regarded as a rearing factor worth to be further investigated, especially when recirculating systems are concerned.     

Oxidative status and histological changes in sea bass larvae muscle in response to high dietary content of docosahexaenoic acid DHA

In previous studies, we observed dystrophic alterations in muscle of 48‐day‐old sea bass fed imbalanced docosahexaenoic acid (DHA) and vitamin E diets. To understand the whole pathological process associated with oxidative stress, a histological study was performed by feeding 14‐day‐old sea bass larvae with microdiets containing different ratios of DHA/vitamin E (1/150, 5/150 and 5/300) for a period of 21 days. Larvae fed diet 1/150 showed no lesions in contrast to larvae fed diets 5/150 and 5/300 where the highest incidence of muscle lesions and thiobarbituric acid reactive substances (TBARS) content was observed. Semithin sections revealed focal lesions consisting of degenerated fibres with hypercontracted myofilaments and extensive sarcoplasm vacuolization affecting both red and white muscle. Ultrathin sections of degenerating muscle fibres showed diffuse dilatation of sarcoplasmic reticulum, disorganized myofilaments and autophagic vacuoles containing myelin figures and dense bodies. Additionally, some macrophages were observed among injured fibres as numerous satellite cells. Results from the study agree with those obtained from previous work, proving the pathological potential of free radicals in sea bass larvae musculature. Moreover, high vitamin E inclusion could not completely protect cell membranes from free radicals action.     

Biochemical differences in lateral muscle of wild and farmed gilthead sea bream (series Sparus aurata L.)

Red and white muscle from specimens of wild and farmed gilthead sea bream (Sparus aurata) were analyzed for histochemical ATPase activity, total protein content, fatty acids, trace element concentrations and myosin isoforms. The fibre type composition of muscle samples was confirmed histochemically by the ATPase reaction, which did not show any differences between the two groups of animals. Myosin ATPase activities, myosin and protein yields were significantly higher in white muscle than in the red muscle and for the red muscle the latter two parameters were higher in wild fish. Fatty acid profiles revealed differences between the two groups of animals, probably because of the fatty acid composition of the diets. Zinc, copper and iron concentrations were higher in red muscle than in white muscle; muscles from wild fish were significantly richer in trace elements. No separation of fast and slow heavy chains of myosin could be obtained on SDS-gel electrophoresis, but two dimensional electrophoresis revealed the presence of three light chains in white muscle (LC1F, LC2F, LC3F), and two main types in red muscle (LC1S, LC2S). Small, variable percentages of LC3F were found in the red muscle samples, especially in the wild fish. It is concluded that the different environmental conditions, experienced by wild and farmed fish, have significantly influenced the biochemical composition of their lateral muscle.     

Life cycle of Caligus rogercresseyi, (Copepoda: Caligidae) parasite of Chilean reared salmonids

Caligus rogercresseyi, [Contrib. Zool. 69 (2000) 137] is the only caligid known to affect the salmon industry in Southern Chile. Economic losses due to reduced fish quality, cost of chemical treatment and outbreaks of other diseases such as the Piscirickettsiosis occur. The life cycle of C. rogercresseyi is described in rainbow trout reared in seawater tanks from observations made under natural conditions of light and temperature between January 1997 and April 1998. Fish were infected with laboratory-cultured larvae obtained from ovigerous females. Rainbow trout were periodically slaughtered for parasite collection and identification. C. rogercresseyi life cycle includes the following stages: two nauplius, one copepodid, four chalimus and the adult. No preadult stage was observed. Timing of the different stages of development was directly dependent on water temperature. The maturation of the eggs or the time for a complete life cycle took place at 45 days in July at 10.3 °C, 31–32 days in April at 12.4 and 12.8 °C, respectively, and at 26 days in November at 15.2 °C. In January, at 16.7 °C, only the appearance of first eggs were observed at 18 days. A simple degree–day (dd) model is proposed for each developmental stage between 4 and 17 °C, where the development rate is a linear function of the average temperature of water. Using this degree–day model, the proportion of fourth stage chalimus was maximum at 172 dd of effective temperature, adult males at 193 degree–days, adult females at 208 dd. The minimum temperature threshold is at 4.2 °C where there is no development of the parasite. The appearance of first eggs occurred at 231 dd and the first pigmented eggs at 277 dd. The temperature-independent degree–days value allowed to predict the timing of C. rogercresseyi life cycle at any temperature within the evaluated range.     

Pharmacokinetics and tissue distribution of oxytetracycline in sea bass, Dicentrarchus labrax, at two water temperatures

A pharmacokinetic study of oxytetracycline (OTC) following an intravascular administration (40 mg/kg) was carried out in sea bass, Dicentrarchus labrax (110 g), at 13.5 and 22 °C water temperature. Blood, muscle and liver samples were taken at 1, 2, 4, 8, 16, 32, 64 and 128 h post-injection. The plasma data were conformed to a two-compartment model. The kinetic profile of the drug was found to be temperature dependent. The absorption half-life (t_1/2) of OTC was 0.98 and 0.192 h at 13.5 and 22 °C, respectively, whereas the elimination half-time (t_1/2β) of the drug was 69 h at 13.5 °C and 9.65 h at 22 °C. The apparent volume of distribution of the drug at steady state [V_d(ss)] was 5.62 l/kg at 13.5 °C and 2.59 l/kg at 22 °C. The mean residence time (MRT) of OTC was found to be 37.7 h at 22 °C and 71 h at 13.5 °C. The total clearance of the drug (CL_T) was calculated to be 73.5 and 68.7 ml/kg/h at 13.5 and 22 °C, respectively.

Liver levels indicated higher OTC values than respective muscle levels at all time points and for both temperatures. The elimination of OTC from tissues tested was faster at the high temperature, whereas the drug was eliminated faster from liver compared to muscle when comparisons are made at the same temperature.