Changes in serum cortisol, metabolites, osmotic pressure and electrolytes in response to different blood sampling procedures in cultured sea bass (Dicentrarchus labrax L.)

This study investigated the effect of five sampling procedures on serum cortisol, glucose, total protein, osmolality, Na⁺, Cl^–, K⁺ and Ca⁺⁺ concentrations in 2-year-old cultured sea bass ( Dicentrarchus labrax L).
Mild disturbance caused by rapid removal of fish and brief handling did not induce significant variation in any of the blood parameters investigated. Confinement and crowding elicited a high and significant increase in serum cortisol, glucose, osmolality, Na⁺, Cl^–, and Ca⁺⁺ concentrations. Exposure to MS 222 (140 mg L^–1) significantly increased osmolality, but not ionic concentration. Site of blood withdrawal (cardiac sinuses/caudal vein) had no effect on the concentration of analysed blood constituents, except for K⁺ levels. Scattered literature of sea bass blood chemistry is reviewed and compared with 'normal' ranges of blood constituents measured in this study. We conclude that it is necessary to select and rigorously execute an opportune blood sampling procedure whenever blood constituents are used as indicators of fish functional state.     

Maturation and fecundity of a stock-enhanced population of striped bass in the Savannah River Estuary, U.S.A

The striped bass Morone saxatilis population in the Savannah River (south-eastern U.S.A.) collapsed in the 1980s, and recent eorts to restore the population have resulted in increased catch-per-unit-eort (CPUE) of striped bass in the Savannah River Estuary (SRE). The abundance of eggs and larvae, however, remain well below historic levels. The primary cause of the population decline was remedied, and environmental conditions seem suitable for striped bass spawning. Regression analysis of data derived from ultrasonic imaging of 31 striped bass resulted in a statistical model that predicted ovary volume well (r²=0.95). The enumeration of oocytes from ovarian tissue samples and the prediction of ovary volume allowed fecundity to be estimated without sacrificing the fish. Oocyte maturation in Savannah River striped bass seemed to progress normally, with oocytes developing to final stages of maturity in larger fish (>750 mm L _T). Additionally, fecundity estimates were comparable to a neighbouring striped bass population. The environmental cues needed to trigger development and release of striped bass oocytes into the SRE appeared to be present. If most of the striped bass females in the SRE are still young (<7 years), the ability to produce large numbers of eggs will be limited. As these young fish mature, egg production probably will increase and the density of striped bass eggs eventually will approach historic levels, provided suitable habitat and water quality are maintained.     

Changes in gill Na+, K+ -ATPase specific activity during seaward migration of wild juvenile chinook salmon

Migration of wild juvenile chinook salmon Oncorhynchus tshawytscha during the first 80 km of their 254 km migration through the Rogue River, Oregon, was significantly slower than that during the last 170 km. Gill Na⁺, K⁺ -ATPase specific activity did not increase significantly during the first 38 km of migration. Specific activities during the next 43 km did increase significantly. Specific activities continued to increase as the fish moved downstream, reaching a maximum within 44 km from the Pacific Ocean.     

Bioactivity of stored luteinizing hormone-releasing hormone analogue (LHRHa) in sea bass, Lates calcarifer Bloch

The spawning induction activity of dissolved and pelleted (D-Ala⁶, Pro⁹ N ethylamide) luteinizing hormone-releasing hormone analogue (LHRHa) stored for various periods was assessed in mature female sea bass. The spawning response of mature fish was reduced significantly after injection of dissolved LHRHa (20 μg kg⁻¹) stored for more than 90 days in a refrigerator (4–10°C) or for more than 30 days at room temperature (28–30°C). Similar to fish administered fresh preparations of LHRHa, fish spawned successfully after injection of a solution of LHRHa previously frozen, subjected to alternate freezing and thawing, exposed to sunlight or implanted pelleted LHRHa (50 ng kg⁻¹) stored at room temperature for 30–120 days. Loss of hormone bioactivity after prolonged storage may have been due to bacterial growth in solubilized preparations. Injection or implantation of stored LHRHa did not influence egg production among treated sea bass. These results demonstrated the relatively prolonged shelf life of stored LHRHa.     

Mercury in tigerfish (Hydrocynus vittatus, Castelnau), green happy (Sargochromis codringtonii, Boulenger) and kapenta (Limnothrissa miodon, Boulenger) from Lake Kariba, Zimbabwe

Concentrations of total mercury were determined in Hydrocynus vittatus (Castelnau), Sargochromis codringtonii (Boulenger), and Limnothrissa miodon (Boulenger) from two localities in Lake Kariba, Zimbabwe.
The mean concentrations of total mercury in H. vittatus from Basin 5 and Basin 2 were 0.08 mg kg⁻¹ and 0.094 mg kg⁻¹, respectively. In S. codringtonii, mean concentrations were 0.004 mg kg⁻¹ and 0.026 mg kg⁻¹ for Basins 5 and 2, respectively. No mercury was detected in L. miodon from Basin 2 while samples from Basin 5 had a mean concentration of 0.069 mg kg⁻¹ (wet weight). Total mercury concentrations were also determined on a dry weight basis.
Within each sampling area, total mercury concentrations were significantly different among species ( P  < 0.05). For H. vittatus and S. codringtonii, total mercury concentrations (in the same species) were not significantly different between the two localities ( P  < 0.05).
The factors causing the observed differences in total mercury between similar species from different localities and among different species in the same locality (sampling area) are discussed. From the observed low levels of mercury in all three species, it was concluded that the mercury constituted 'background levels'. These levels are below the maximum concentrations permissible in human fish foods.     

Energy and ration requirements of juvenile Pacific halibut (Hippoglossus stenolepis) based on energy consumption and growth rates

Growth of captive juvenile Pacific halibut was linearly related to energy consumption (J g⁻¹ day⁻¹) at 4°C by the following equation: growth (% body weight (b.w.) day⁻¹)=0–007 (consumption J g⁻¹ day⁻¹)– 0.192; r² =0.81. Weight gain was independent of size for fish between 9 and 7000 g when growth was expressed as a function of consumption in J g⁻¹ day⁻¹. Maintenance ration determined in feeding–growth experiments averaged 27.4 J g⁻¹ day⁻¹ at 4–0°C. Small halibut ate significantly more food than large fish. Single meals following 2 day fasts averaged 4.1% b.w. for halibut under 100 g, 1.72% b.w. for 1.2 kg fish and 1.1% B.W. for 6.8 kg fish. Both large and small size categories of halibut tended to evacuate their meal in about 3 days even though small fish ate relatively larger meals. Minimum estimates for daily ration to achieve growth rates observed in the Gulf of Alaska were approximately 0.5 to 2.4% b.w. day⁻¹ depending on fish size and whether northern shrimp or yellowfin sole were their prey.     

Routine metabolism of juvenile spot, Leiostomus xanthums (Lacépède), as a function of temperature, salinity and weight

Routine oxygen consumption rates of juvenile spot, Leiostomus xanthums , were measured over a range of temperatures, salinities and fish weights. As predicted, Q O₂ increased with temperature and decreased with body weight. However, Q O₂ decreased with decreasing salinity and did not show the expected minimum at isosmotic concentrations. The data are best described by the relationship: log₁₀ Q O₂ (mg O₂ g⁻¹ h⁻¹) = 0.129 log_lo salinity (%0) + 1.604 log₁₀ temperature (°C)-0.1401og₁₀(g)-2.767.     

Ionic regulation and Na+,K+-ATPase activity in gills and kidney of the Antarctic aglomerular cod icefish exposed to dilute sea water

When Notothenia neglecta was exposed to diluted, half strength, sea water for 6 h or 10 days, serum concentrations of Cl^-, Na⁺, K⁺ and Mg²⁺ did not differ from those of sea water controls. This indicates that the fish were capable of both short- and long-term regulation. Renal Na⁺,K⁺-ATPase activity decreased after a 6 h exposure to diluted sea water, but there were no differences between diluted sea water and controls after 10 days of exposure.     

Swimming performance and metabolism of 0+ year Thymallus arcticus

The prolonged swimming speed and metabolic rate of 0+ year Arctic grayling Thymallus articus were examined with respect to current velocity, water temperature and fish size, and compared to conditions fish occupy in the river. Oxygen consumption (mg O₂ h⁻¹) increased with fish mass and temperature (6–23° C), with a steep increase in metabolic rate between 12 and 16° C. Absolute prolonged swimming speed (cm s⁻¹) increased rapidly with fish size (total length, L _T, and mass), however, fish in the natural stream habitat occupied current velocities between 15 and 25 cm s⁻¹ or 4  L _T s⁻¹, approximately half their potential prolonged swimming speed (10  L _T s⁻¹).     

Energy savings in sea bass swimming in a school: measurements of tail beat frequency and oxygen consumption at different swimming speeds

Tail beat frequency of sea bass, Dicentrarchus labrax (L.) (23.5 ± 0·5 cm, L_T ), swimming at the front of a school was significantly higher than when swimming at the rear, for all water velocities tested from 14·8 to 32 cm s⁻¹. The logarithm of oxygen consumption rate, and the tail beat frequency of solitary swimming sea bass (28·8 ± 0·4 cm, L_T ), were each correlated linearly with swimming speed, and also with one another. The tail beat frequency of individual fish was 9–14% lower when at the rear of a school than when at the front, corresponding to a 9–23% reduction in oxygen consumption rate.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

Extracellular Calcium Concentration Affects Infectivity of Ichthyophthirius (Ciliophora) Theronts

Tomonts and their theront offspring of the hymenostomatid fish parasite Ichthyophthirius multifiliis were exposed to calcium levels from 0 to 0.8 mM Ca^2+. The survival and reproductive rates of tomonts in the absence of extracellular calcium were not significantly different from rates of tomonts provided calcium. Theronts that developed in the absence of calcium, however, were not infective for Ictalurus punctatus even when the extracellular magnesium concentration was doubled. Theronts that developed in 0.10 mM Ca²⁺ were infective (0.77 trophonts/mm² of pectoral fin) to essentially the same extent as theronts provided 0.33 mM Ca^2+. Infectivity of those provided 0.8 mM Ca²⁺ was 1.79 trophonts/mm² of fin, similar to that of theront controls. Theronts deprived of extracellular calcium as they developed contained significantly fewer secretory mucocysts than did theronts provided 0.1 to 0.8 mM Ca²⁺ although no significant differences among groups occurred with respect to abundance of crystalline or differentiating mucocysts. Theronts deprived of extracellular calcium also had swollen or enlarged mitochondria and abnormal crystalline mucocysts.     

Salinity tolerance of two tropical fishes, Oreochromis aureus and O. niloticus. I. Biochemical and morphological changes in the gill epithelium

Cichlids of the genus Oreochromis are fish of economic importance in African countries. They tolerate brackish water, however, with great variations between species. In this work, two species, both from the Ivory Coast but of different origins, O. niloticus (field and laboratory strains) and O. aureus (field strain) were compared during osmotic challenges (10, 20 and 30%o salinity) in order to provide physiological support for their specific behaviour when confronted with natural hypertonic environments. Tolerance to salinity was assessed by correlated observations on gill structure, plasma sodium levels and gill Na⁺/K⁺ ATPase activity. In fresh water (FW), all fish presented a gill epithelium structure characteristic of FW stenohaline fish: no chloride cells (CC) on the lamellae and few CC on the filaments. An increase in external salinity induced the proliferation of CC on filaments, a feature typical of seawater teleosts. This change in gill structure was accompanied by an increase of gill Na⁺/K⁺ ATPase activity. In the most tolerant strains, plasma Na⁺ did not change, indicating successful ion regulation in the hypertonic media. With regard to potential interest of field strains in fish culture, O. aureus acclimated more easily to brackish water than O. niloticus . Interestingly, O. niloticus , kept for several generations in the laboratory, performed best in our challenge studies. Plasma Na⁺ levels and gill CC proliferation upon transfer to an isotonic medium may be the parameters of choice when testing these fish for their response to a salinity change.     

In vitro analysis of intestinal absorption of cadmium and calcium in rainbow trout fed with calcium- and cadmium-supplemented diets

The protective effects of dietary Ca²⁺ supplementation against Cd accumulation in rainbow trout Oncorhynchus mykiss fed with Cd-contaminated food were evaluated in relation to chronic changes in intestinal absorption rates. The changes were measured ' in vitro '. The control diet contained c. 20 mg Ca²⁺ g⁻¹ food and 0·25 μg Cd g⁻¹ food; the experimental diets were supplemented with CaCO₃ and Cd(NO₃)₂·4H₂O to levels of 50 mg Ca²⁺ g⁻¹ food and 300 μg Cd g⁻¹ food, alone and in combination. The Ca²⁺ and Cd absorption rates were measured using radiotracers (⁴⁵Ca, ¹⁰⁹Cd) at total Ca²⁺ and Cd concentrations of 3·0 and 0·12 mmol l⁻¹, respectively in the intestinal saline. Chronically elevated dietary Cd caused a significant increase in Cd absorption rate by up to 10-fold at 30 days in the mid-intestine. The high Ca²⁺ diet prevented this up-regulation of Cd transport rate. Conversely, intestinal Ca²⁺ absorption was significantly increased by two- to five-fold by the Ca²⁺-supplemented diet at 30 days in both the mid- and posterior intestine, and this effect was eliminated when Cd was simultaneously elevated in the diet. Ca²⁺ and Cd probably interact at common pathways and transport mechanisms in the intestine, though independent pathways may also exist.     

Rapid data collection and assessment of the biology of Acanthurus nigrofuscus at Woleai Atoll, Micronesia

Traditional community fishing methods commonly employed in the tropical Pacific were used to generate information on the fishery biology of Acanthurus nigrofuscus at Woleai Atoll, Micronesia, over a short time period. A simple depletion model was used to estimate the biomass of A. nigrofuscus at four back reef lagoon sites at Woleai, using two different fishing methods; spear fishing and drive-in-net fishing. The mean biomass and density of A. nigrofuscus on the lagoon reefs was 8000 g ha ⁻¹ and 183 fish ha ⁻¹ respectively, with a total estimated standing stock for the lagoon of 91 500 fish or a biomass of 4·0 t. The size frequencies of fish caught by spear fishing were biased towards larger sized individuals, while those from drive-in-net fishing were thought to be more representative of the true population size frequencies. Variation in the density and biomass of A. nigrofuscus at the four reef sites was thought to be due to the length of time between episodes of community fishing at each reef site. The sex ratio (male: female) of A. nigrofuscus was significantly different from unity (1: 0·47) and males grew larger than females. Sexually mature fish were present in all size classes above the minimum capture length and spawning activity was greatest during the period of the full moon.     

Acute toxicology to an estuarine teleost of mixtures of cadmium, copper and zinc salts

Effects of mixtures of chloride salts of cadmium, copper and zinc on survival, whole body residues, and histopathology of mummichog, Fundulus heteroclitus (L.), were investigated in synthetic sea water at 20‰ salinity and 20°C. Mixtures of Cu²⁺ and Zn²⁺ as indicated by 96 h bioassay studies produced more deaths than expected on the basis of toxicities of individual components. Concentrations of Cd²⁺ not ordinarily lethal exerted a negative effect on survival of fish intoxicated by salts of copper, zinc, or both.
Atomic absorption determinations of Cd, Cu, and Zn residues in mummichog which survived 96 h exposures to each of these toxicants provided useful indices of total body burdens for these metals. Residues from survivors held in mixtures, especially Cd²⁺ and Zn²⁺ mixtures, did not conform to patterns observed for single elements. Whole body aggregates of Cd, Cu, and Zn from dead mummichogs were of limited worth owing to possible accumulation of these metals from the medium after death.
Renal and lateral line canal lesions were noted in all fish subjected to copper concentrations of 1 mg/1 and higher. Renal lesions observed in fish immersed in mixtures of Cu²⁺ and Cd²⁺ assumed a damage pattern characteristic of Cd²⁺; with mixtures of Cu²⁺ and Zn²⁺, lesion were typical of Cu²⁺-induced damage. Lesions induced in lateral line epithelium by Cu²⁺ were not affected by either Cd²⁺ or Zn²⁺. Epithelia lining the oral cavity were necrotized by the caustic action of high levels of Zn²⁺ (60 mg/1) and of Cu²⁺ (8 mg/1).     

Seasonal changes in androgen levels in stream- and hatchery-reared Atlantic salmon parr and their relationship to smolting

In stream-reared Atlantic salmon Salmo salar , plasma androgens were significantly greater in mature male parr than immature males and females in October, but had declined by January and did not differ significantly from immature fish throughout the spring. Immature fish in March were significantly larger and had greater gill Na⁺, K⁺-ATPase activity than their previously mature counterparts. Bimodal growth distribution was seen in hatchery-reared Atlantic salmon and a proportion of the male fish in the lower mode matured. Plasma testosterone (T) and 11-ketotestosterone (11-KT) were significantly elevated from September to December in mature male (1+ year) parr. In January, plasma androgens had declined in mature males and did not differ significantly from immature fish. By May all the hatchery fish were large enough to smolt and a proportion of the previously mature males had increased gill Na⁺, K⁺-ATPase activity. Therefore elevated androgens in the previous autumn do not prevent smolting. Parr with higher plasma T and 11-KT in April and May, that are presumably beginning to mature, had lower gill Na⁺, K⁺-ATPase activity, indicating that future maturation and associated increases in androgens may inhibit smolting.     

Salinity effects on oxygen consumption, gill Na+, K+-ATPase and ion regulation in juvenile coho salmon

The metabolic response of juvenile coho salmon Oncorhynchus kisutch to different salinities was examined, using whole-animal oxygen consumption rates and gill Na⁺, K⁺-ATPase activities as indicators of osmoregulatory energetics. Coho salmon smolts were acclimated to fresh water (FW), isosmotic salinity (ISO, 10‰) and sea water (SW, 28‰) and were sampled for up to 6 weeks for plasma levels of cortisol, glucose and ions (Na⁺, K⁺, Cl⁻), gill Na⁺, K⁺-ATPase activity and oxygen consumption rates. Following an initial adjustment period, plasma constituents in SW fish returned to near-FW values, indicating that the fish were acclimated to SW by day 21. Gill Na⁺, K⁺-ATPase activities on days 21 and 42 were lowest in ISO, higher in FW and highest in SW. This result is consistent with the idea that less energy would be required to maintain ion balance in an isosmotic environment, where the ionic gradients between extracellular fluid and water would be minimal. Oxygen consumption rates of swimming fish (1 body length s⁻¹), however, did not differ significantly between the three test salinities after 6 weeks. The results of this study suggest that the metabolic response of juvenile salmonids to changes in salinity is dependent on life-history stage (e.g. fry v . smolt), and that oxygen consumption rates do not necessarily reflect osmoregulatory costs.     

PHOTOSYNTHETIC BICARBONATE UTILIZATION BY A TERRESTRIAL CYANOBACTERIUM, NOSTOC FLAGELLIFORME (CYANOPHYCEAE)

The photosynthetic characteristics of the terrestrial cyanobacterium, Nostoc flagelliforme , after complete recovery by rewetting, was investigated to see whether it could use bicarbonate as the external inorganic carbon source when submerged. The photosynthesis–pH relationship and high pH compensation point suggested that the terrestrial alga could use bicarbonate to photosynthesize when submerged. The photosynthetic oxygen evolution rates were significantly inhibited in Na ⁺ -free and Na ⁺ + Li ⁺ media but were not affected by the absence of Cl ⁻ , implying that the bicarbonate uptake was associated with Na ⁺ / HCO₃ ⁻ symport rather than Cl ⁻ /HCO₃ ⁻ exchange system.