Protein synthesis, nitrogen excretion and long-term growth of juvenile Pleuronectes flesus

This study aimed to measure protein synthesis using a stable isotope method, investigate protein-nitrogen flux in a flatfish Pleuronectes flesus , and use the data to test the hypothesis that individual differences in growth efficiency were related to individual differences in protein-nitrogen flux mediated through differences in protein synthesis and degradation. Three measurements of protein-nitrogen flux via consumption, protein synthesis and nitrogenous excretion were made for individual flounder during a 212-day period and fractional rates of protein-nitrogen flux were scaled for a 50–g flounder to provide mean values for protein consumption (2·11 ± 0·21% day⁻¹), protein synthesis (2·08±0·23% day⁻¹), protein growth (0·71±0·06% day⁻¹) and protein degradation (1·37±0·24% day⁻¹). Mean rates of nitrogenous excretion were 0·142 mg N g⁻¹ day⁻¹ and 0·047 mg N g⁻¹ day⁻¹ for ammonia and urea, respectively. Individual flounder had different protein growth efficiencies and this was correlated negatively and significantly with mean rates of protein synthesis ( r - 0·70; P <0·05) and degradation ( r - 0·67; P < 0·05) and correlated positively and significantly with the efficiency of retaining synthesized protein ( r +0·63, P <0·05). This supported the proposed hypothesis that flounder which grow more efficiently achieve this through adopting a low protein turnover strategy.     

The combined effect of feeding time and ration on growth performance and nitrogen metabolism of greenback flounder

Greenback flounder Rhombosolea tapirina ( c. 2 g) fed to satiation had significantly ( P <0·01) higher feed consumption in the evening than in the morning whereas there was no difference between feeding times for flounder fed restricted rations (1 or 2% body weight per day) because they consumed all of the ration. Differences in growth performance were due to feeding time and ration. Carcass moisture, lipid and energy content were significantly ( P <0·001) different between rations; length gain was significantly affected by feeding time ( P <0·05) and ration ( P <0·001); weight gain showed a significant ( P <0·001) interaction between feeding time and ration. The relationship between feed consumption and specific growth rate showed that the exponential gradient was significantly higher ( P <0·01) for the evening fed fish and indicated feed efficiency for evening fed fish increased as feed consumption increased. Urea excretion increased from 12–20 to 58–63% of total nitrogen excretion at the 1 and 3% rations, respectively. Ammonia and urea excretion were significantly affected by ration ( P <0·001) and feeding time ( P <0·05). Fish fed the 2% ration in the evening had higher growth efficiency and significantly ( P <0·01) lower rates of urea excretion than fish fed 2 or 3% ration in the morning. It is suggested that the higher energetic costs associated with differences in ammonia and urea excretion contributed to differences in growth efficiency.     

Consumption of deep-sea shrimp by bigeye flounder Hippoglossina macrops in fishing grounds off northern Chile

Feeding of the bigeye flounder Hippoglossina macrops on the shrimp Heterocarpus reedi was analysed between 20 November and 4 December 1995. Feeding on H. reedi intensified between 0900 and 1600 hours with a second, smaller peak between 2300 and 0200 hours. Assuming an exponential gastric evacuation model, the gastric evacuation rate was estimated as 0·197 % W h ⁻¹ (95% CI=0·025–0·369). The daily ration decreased latitudinally from north to south from 3·62 to 2·66 and from 2·06 to 0·41 %W , respectively. Consumption was related positively to shrimp biomass and influenced by flounder size structure in the three fishing zones analysed and was estimated as 0·08–0·02% of the total shrimp biomass.     

The effect of meal size and meal duration on food anticipatory activity in greenback flounder

Latency of food anticipatory activity (FAA) in greenback flounder Rhombosolea tapirina was about 21 days. Fish fed at meal sizes of 0·25 and 0·5% W day⁻¹ exhibited FAA under meal durations of 1, 3 and 7 h. Fish fed at 1·5% W day⁻¹ showed FAA only at a meal duration of 1 h. At each meal size, FAA was shorter and lower the longer the duration of the meal. The mean durations of FAA and post-feeding activity were correlated positively ( r =0·87; P <0·01; n =7). FAA persisted for <3 days during food deprivation. It is suggested that greenback flounder was capable of evaluating the energetic and temporal impacts of a single daily meal.     

Seasonal changes in the intestinal mucosa of winter flounder, Pseudopleuronectes americanus (Walbaum), from Passamaquoddy Bay, New Brunswick

Winter flounder from Passamaquoddy Bay, N.B. undergo an annual fast from November to May which results in a decrease in the slope of the length-weight relationship (3·17 to 2·54), in the condition factor (9 to 12%), in the liver (75%) and white muscle (24%) lipid contents, and an increase in muscle water content (2·4%). Winter flounder appear to have sufficient lipid reserves to support the winter fast, as muscle water content declined only at the onset of feeding.
The intestine could be divided into pyloric caeca (4), foregut, midgut and hindgut. Mucosal folding was reduced in all sections of the intestine during the fast. Goblet cell number declined, but little change in enterocyte ultrastructure was observed. Intestinal length remained the same, although the caeca shortened. Overall, mucosal mass declined by 57% from May to January, while surface area declined by 50%. This value is less than that in literature reports for a fast of shorter duration in freshwater rainbow trout. We propose that the continued need for salt and water transport for osmoregulation maintains the proximodistal gradient of mass and surface area and ameliorates the effect of starvation on mucosal mass and area.     

Microsatellite analysis as a tool for discriminating an interfamily hybrid between olive flounder and starry flounder

An interspecific artificial hybrid was produced between two economically important aquaculture flatfish: olive flounder (Paralichthys olivaceus) and starry flounder (P. stellatus). This hybrid displays the rapid growth characteristic of the former and tolerance to low temperatures and low salinity of the latter, but the genetics of inheritance in this hybrid have not been elucidated. Polymorphic microsatellite markers developed for P. olivaceus and P. stellatus were tested to determine if these markers can be used for analysis of parentage and genetic inheritance. Multiplex PCR using two primer sets that were specific to each species produced PCR products of different sizes; these could be used for the identification of interspecific hybrids. Among the 192 primers derived from olive flounder, 25.5% of the primer sets successfully amplified genomic DNA from starry flounder, and 23% of the 56 primer sets originating from starry flounder amplified DNA from olive flounder. Analysis of genetic inheritance in the hybrid using seven of the 62 microsatellite markers common to both species demonstrated classic Mendelian inheritance of these markers in the hybrid progeny, with the exception of one locus identified as a null allele in the hybrid. These results demonstrate that cross-specific microsatellite markers can be used tools for parentage analysis of hybrid flatfish, for mapping quantitative trait loci, for marker-assisted selective breeding, and for studies of the evolution of fish.     

Effects of cyclic and constant hydrostatic pressure on norepinephrine and epinephrine levels in the brain of flounder

The effects of cyclic and constant hydrostatic pressure on the norepinephrine and epinephrine content in discrete regions of the brain of European flounder Platichthys flesus were studied. After a 14 day exposure to cyclic hydrostatic pressure with a tidal period of 12·4 h and with a maximum peak of 800 kPa (range 200–800 kPa of absolute hydrostatic pressure), fish showed a highly significant decrease in norepinephrine content when compared to control animals held at constant atmospheric pressure. No changes were detected in fish submitted to a constant hydrostatic pressure of 800 kPa.     

Early growth and development of reciprocal hybrids of the starry flounder Platichthys stellatus and stone flounder Kareius bicoloratus

Larval growth and development of hybrid flounder were observed and compared with those of their parent species. The reciprocal hybrids of female starry flounder Platichthys stellatus and male stone flounder Kareius bicoloratus (hybrid Sb) and of female K. bicoloratus and male P. stellatus (hybrid Bs) both survived and grew to juveniles. Development was divided into nine stages (A–I). Many of the hybrids' traits were identical and intermediate to those of their parents. The position of the eye, however, was primarily sinistral in both hybrids (80% in Sb and 76% in Bs), a trait possessed by P. stellatus (80%) in the western Pacific Ocean. The daily growth rates of the larvae were similar. In the parent species, development was more rapid in P. stellatus than in K. bicoloratus whereas rate of development was intermediate in both Sb and Bs hybrids. The size at settlement [standard length (L_S) at stage H (mean ± s.d. )] was 9·82 ± 1·47 mm for the hybrid Sb and 9·99 ± 0·90 mm for the hybrid Bs, while the minimum age at metamorphosis (initial age at stage H) was 29 days after hatching (DAH) in both hybrids. In comparison, L_S at settlement in parent species was 6·43 ± 0·25 mm for P. stellatus and 12·87 ± 1·29 mm for K. bicoloratus. Minimum age at metamorphosis for the parents was 23 DAH at stage G in P. stellatus and 34 DAH at stage H in K. bicoloratus. Thus, the timing of settlement of hybrids was different from that of their parent species. These traits may occur with high frequency in a natural habitat.     

A method for measuring oxygen consumption in isolated perfused gills

A method is described for measuring respiration in isolated perfused flounder gills experiencing pressures and flows similar to those seen in vivo . Mean oxygen consumption of 13 preparations bathed and perfused in identical saline was 5·00 ± 0·75 (s.e.) μ mol h⁻¹ g wet⁻¹, whilst that of five preparations perfused with saline but bathed in sea water (32 mg l⁻¹) was 12·06±2·39 (s.e.) μmol h⁻¹ g wet⁻¹. The oxygen consumption of the seawater bathed gills was significantly higher (P<0·05) than that in saline bathed gills. These results provide direct evidence both of the high metabolic activity of the gill under normal perfusion conditions and of the increased energy expenditure of the giil in hyperosmotic, compared to isosmotic, environments.     

Opercular differential pressure as a predictor of metabolic oxygen demand in the starry flounder

The feasibility of using a differential pressure sensor connected to an acoustic telemetry device to monitor opercular activity as a correlate of oxygen consumption was investigated. Four starry flounders Platichthys stellatus were fitted with a miniature differential pressure sensor mounted close to the operculum. A cannula was connected to the sensor and inserted under the operculum, inside the branchial cavity. Measurements of oxygen consumption and opercular activity were carried out over a broad range of metabolic activity, from the post‐surgery stress (high metabolic rate) to routine metabolic rate the following day. Relationships between differential pressure changes (rate and amplitude) were highly correlated with oxygen consumption ( r ² = 0·74 and 0·60 respectively). The results indicate that monitoring opercular activity offers an alternative method for measuring aerobic metabolism in free‐swimming fishes in nature.     

Changes in growth performance and proximate composition in Japanese flounder during metamorphosis

Morphological changes are described in Japanese flounder Paralichthys olivaceus larvae and juveniles with emphasis on growth during the period of metamorphosis. Ontogenetic changes in condition factor and lipid, glycogen and protein levels were also analysed to determine the utilization of stored energy. Fish grew from 6·6 to 20·3 mm L _T(1·15 to 84·4 mg in mass, M ) during the period from 11 to 40 days after hatching (DAH) at 19·3° C. Per cent specific growth rate per day (% G day⁻¹) for wet mass was lowest during the metamorphic phase (21–30 DAH) compared to pre‐(11–20 DAH) and post‐metamorphic (31–40 DAH) phases. When L _T and M were expressed as     , the b value was highest during the pre‐metamorphic phase and lowest during the metamorphic phase. These findings indicate that the developmental changes that occur during metamorphosis of Japanese flounder are closely related to the growth pattern. Moisture, lipid and glycogen contents were also at the lowest level during metamorphosis compared to pre‐ and post‐metamorphosis, which suggest that Japanese flounder use their energy reserves to accomplish metamorphosis due to an apparent decline in feeding during this period.     

Compensatory growth of juvenile brown flounder Paralichthys olivaceus (Temminck & Schlegel) following thermal manipulation

The compensatory growth of juvenile brown flounder Paralichthys olivaceus (body mass c. 12 g) following different thermal exposure was investigated. Fish were exposed to one of the five temperatures: 8·5 ( T _8·5), 13·0 ( T _13·0), 17·5 ( T _17·5), 22·0 ( T _22·0) and 26·5° C ( T _26·5) for 10 days and fish grew best at 22·0° C. Then the water temperature in all treatments was equably adjusted to 22·0° C over 3 days. At the end of the following 30 days after temperature adjustment, there were no significant differences between body masses of fish in the different treatments (wet body mass at the end of the experiment ranged from 22·13 to 24·56 g). Results indicated that the juvenile P. olivaceus achieved complete compensatory growth. Analysis of the dynamics of the feeding rates and feed conversion efficiencies indicated that compensatory growth of the fish experienced low temperature ( T _8·5, T _13·5 and T _17·5) or high temperature ( T _26·5) exposure was mainly dependent on increasing feed intake (hyperphagia) and possibly by improvement in feed conversion efficiency. The moisture content was not affected by different temperature exposure significantly. The lipid and energy content of juvenile P. olivaceus in T _8·5, however, were significantly lower than other treatment. Results of the current study indicate that a short period of low or high temperature exposure may not affect annual growth, but may affect lipid and energy deposition.     

Differences in size and growth rates of male and female migrating Japanese eels in Pearl River, China

The Sr/Ca ratios in otoliths of silver Japanese eels Anguilla japonica , in Pearl River, China, indicated that both sexes did not stay in brackish water and grew in fresh water from the glass eel stage until spawning migration. This did not support the hypothesis that females tended to distribute upstream and males might be restricted to estuaries. The back-calculated total length of males at glass eel stage was not significantly different from that of females, indicating that the hypothesis that small glass eels became males and larger ones became females may not be true. The mean (±S.D.) age and total length of males at migration were 6·4±1·6 years and 48·3±4·5 cm, which were significantly smaller than for females, 8·3±1·6 years and 61·4±4·1 cm. The age of migration was related inversely to growth rate for both sexes. Growth parameters of the von Bertalanffy growth equation were K =0·21 cm year°1, L _∞=55·7 cm and t _o=-0·55 year for males and K =0·14 cm year⁻¹, L _∞=77·5 cm and t _o=-0·60 year for females. The difference in asymptotic length ( L _∞) between males and females may be because females postpone migration to achieve larger size for maximizing reproductive success.     

An RNA:DNA-based growth model for young-of-the-year winter flounder Pseudopleuronectes americanus (Walbaum)

A laboratory calibration experiment was conducted to determine the relationship between nucleic acid-based variables and growth rate in young-of-the-year winter flounder Pseudopleuronectes americanus . Three temperatures and three feeding levels were used to produce a variety of growth rates. Nucleic acid analyses were conducted on white muscle tissue using an ultraviolet absorption assay. RNA concentration (μg mg⁻¹ wet tissue mass) and the ratio of RNA:DNA ( R _RD) were positively correlated with a mass-based instantaneous growth coefficient ( G _M) ( r = 0·42 and 0·72, respectively). Fifty-one per cent of the variability in growth rate was explained by the simple linear regression G _M=−0·02615 + 0·00848 R _RD ( P < 0·001). This model can be used to estimate recent growth rates for early juvenile winter flounder (27–52 mm standard length) at temperatures ranging from 11 to 24° C.     

Influence of salinity on the migration of postlarval and juvenile flounder Pleuronectes flesus L. in a gradient experiment

The behaviour of the flounder Pleuronectes flesus was observed in an experimental aquarium that consisted of five connected units with decreasing salinity from 20 to 15, 10, 5 and 0·5. This experimental aquarium was highly effective for studying behaviour in salinity gradients, because the gradient was relatively stable. After 4 days of observation, significantly more flounder were found in water with a salinity of 0·5, indicating a preference for fresh water. The total length of the flounders ranged from 7·5 to 21 mm. The majority of larvae had already started eye‐migration, however, the longer specimens had completed metamorphosis. The migration towards low salinities was observed to increase with ontogenetic development.     

Substratum selection by juvenile flounder Platichthys flesus (L.): effect of ephemeral filamentous macroalgae

Selection of substrata representing habitats with or without filamentous vegetation by juvenile flounder Platichthys flesus was investigated in laboratory experiments and a field study to assess the effect of the increasing occurrence of ephemeral filamentous macroalgae in shallow nursery areas and its potential effect on flounder recruitment. In the laboratory experiments, 79% of juvenile flounder (24–99 mm total length, L _T) preferred bare sand substrata in comparison to substrata with simulated filamentous vegetation. Substratum preference did not change with fish size. Field sampling using a drop trap (1 m²) in a vegetated (>50% coverage of ephemeral macroalgae) habitat in June, July and August showed small flounder (mean L _T= 37·3 mm) were caught more often in samples with less vegetation. In contrast, larger flounder (mean L _T= 57·2 and 79·7 mm in July and August, respectively) were more evenly distributed in relation to the distribution of vegetation. The results of this study indicate that the increase in ephemeral macroalgae observed in recent years potentially reduces the quantity and quality of suitable nursery habitats for juvenile flounder, which could have detrimental consequences to the overall recruitment of flounder in coastal areas.     

Winter behaviour of juvenile Atlantic salmon Salmo salar L. in experimental stream channels: effect of substratum size and full ice cover on spatial distribution and activity pattern

Activity and choice of areas offering different cover (substratum or surface ice) for juvenile Atlantic salmon Salmo salar were studied in experimental stream channels during winter. Channels were completely ice covered between December and March. During this period, the ice thickness increased from 50 to 300 mm after which 50% of the ice was experimentally removed and followed by c. 2·5-fold increase in discharge to simulate the effects of spring flood. Large substrata provided preferred habitats but areas with small substratum sizes were also used when full surface ice provided above-stream cover and the stream discharge was relatively low. The fish remained nocturnal throughout the study but the level of day activity significantly increased as the surface ice became thicker. Maximum movement distance during a 24 h period and homing-at-dawn behaviour remained at a constant level throughout the main winter, but significantly changed during the simulated spring flood (mean ± s . e . maximum extent of movements within 24 h increased from 1·1 ± 0·1 to 3·0 ± 0·5 m; homing behaviour decreased from the highest level of 89·3 to 34·6% during spring flood). Overwinter survival was high (92·9%). Relative mass increase during the study ranged from –8·3 to 28·5%, and 84% of the juvenile Atlantic salmon gained mass. The highest rates of mass increase were associated with frequent movements between areas of different substratum size. The results indicate that during winter: (1) Atlantic salmon parr preferred large substratum cover compared with surface ice cover at the fish densities studied here, (2) juvenile Atlantic salmon were predominantly nocturnal but diurnal activity increased as surface ice became thicker and (3) increase in water discharge during spring altered the behaviour of juvenile Atlantic salmon and may have caused additional habitat shifts.     

Effects of temperature and delayed initial feeding on the survival and growth of Japanese flounder larvae

The effects of the timing of initial feeding (0, 1, 2, 3 and 4 days after yolk exhaustion) and temperature (15, 18 and 21° C) on the point‐of‐no‐return (PNR), survival and growth of laboratory‐reared Japanese flounder Paralichthys olivaceus larvae were studied under controlled conditions. The larvae reached PNR on 7·7, 5·2 and 4·2 days‐post‐hatching (dph) at 15, 18 and 21° C, respectively. At each temperature, larval growth did not differ significantly among the delayed initial feedings 1 day before PNR but decreased significantly in larvae first fed after that. In the treatments where initial feeding was equally delayed, larvae grew significantly faster at 18 and 21° C than at 15° C. The larvae survived apparently better at 15 and 18° C than at 21° C when initial feeding was equally delayed. At each temperature, survival of the larvae first fed before PNR did not differ noticeably, while delayed initial feeding after that apparently reduced their survival. These results indicated that there existed a negatively temperature‐dependent PNR in the Japanese flounder larvae. Survival and growth of the larvae strongly depended on temperature as well as the timing of initial feeding. High temperature accelerated the yolk exhaustion and growth of the larvae and thus reduced their starvation tolerance and survival. To avoid potential starvation mortality and obtain good growth, the Japanese flounder larvae must establish successful initial feeding within 2 days after yolk exhaustion at 15° C and within 1 day at both 18 and 21° C.     

Oxygen consumption rates of tilapia in fresh water, sea water, and hypersaline sea water

Whole animal oxygen consumption rates and plasma constituents were determined in the tilapia O. mossambicus , acclimated for 1 month in fresh water, sea water, and 1·6 × sea water. Oxygen consumption rates for the three water salinities were: 177·2 ± 16·86, 78·6 ± 2·32, and 195·4 ± 15·39 mg O₂ kg⁻¹ h⁻¹ (means ± 1 s.e.), respectively. Plasma prolactin (tPRL₁₈₈) concentration was significantly lower in 1·6 × sea water compared to fresh and sea water. There were no significant differences among mean plasma cortisol concentration and lysozyme activity. Ventilation was significantly higher in fish in sea water compared to the fish in fresh and 1·6 × sea water. The lowest oxygen consumption rates were found in fish acclimated to sea water. That salinity is probably closest to the brackish waters from which they were captured in the wild, and this agreement likely reflects the selection for optimal morphological and physiological characteristics to live in that environment.     

Identification of natural hybrids of gibel carp Carassius auratus gibelio (Bloch) and crucian carp Carassius carassius (L.) from lower Dyje River floodplain (Czech Republic)

Morphometric and genetic variation were examined in parental Carassius auratus gibelio and Carassius carassius individuals, and their natural hybrids. Of meristic traits, only the number of gill rakers clearly distinguished hybrids (39·4 ± 1·4) from parental C. a. gibelio (48·3 ± 0·7) and C. carassius (28·6 ± 1·1). MtDNA sequences showed that the hybrids were descendants of female C. a. gibelio . Microsatellite analysis confirmed the presence in hybrids of variants typical of C. a. gibelio and C. carassius .