Norman Y.S. Woo

Effects of salinity and nutritional status on growth and metabolism of Sparus sarba in a closed seawater system

A re-circulating seawater system employing biological filtration was set up to assess the growth potential of sea bream (Sparus sarba) under the combined effects of salinity (7, 15, 35 p.p.t.) and dietary protein level (30, 35, 40, 45, 50, 55%). The re-circulating system was able to sustain growth of sea bream at high stocking density (3 g 1−1), possibly by minimising stress. Typical stress indices such as serum cortisol, glucose and lactate levels were reduced in sea bream cultured within the recirculating system. Growth rates and protein efficiency ratios of sea bream cultured at 15 p.p.t. were consistently higher than those at other salinities. Growth enhancement at 15 p.p.t. was accompanied by a reduction in oxygen consumption, ammonia excretion rates, liver lipid levels and hepatic glucose-6-phosphatase activity. However, hepatic hexokinase activity was stimulated at 15 p.p.t. Most of these effects were more evident in fish fed high protein levels. These data suggest that growth enhancement at 15 p.p.t. may be explained by (1) reduction of metabolic cost of osmoregulation, and (2) reorganisation of metabolism, which would allow protein sparing in favour of a shift towards preferential utilisation of carbohydrate and lipid.

Haloplasticity of black seabream (Mylio macrocephalus): Hypersaline to freshwater acclimation

Black seabream (Mylio macrocephalus) were acclimated to various salinities (50, 33, 12 and 6‰) for eight months. Acclimation of fish to 6‰ for eight months allowed successful adaptation to freshwater (0‰) for a further 21 days without mortality. This is the first report of freshwater acclimation of a “true” marine fish for an acceptable experimental duration. Osmoregulatory and metabolic strategies were characterized via alterations in branchial chloride cell (CC) numbers and surface ultrastructural morphometrics along with changes in serum chemistry, muscle moisture, liver glycogen and branchial, renal, hepatic and intestinal enzyme activities. Branchial CC numbers were elevated in 50 and 6‰ environments; however, freshwater acclimation resulted in return to low numbers. Branchial Na+-K+-ATPase activity was generally higher in 50 and 33‰ environments and exhibited a declining trend in 12 and 6‰ environments. Freshwater acclimation resulted in a marked elevation in branchial Na+-K+-ATPase activity. Elevated CC exposure areas were typically found at salinity extremes. Serum Na+, Cl– and muscle moisture content did not vary between groups acclimated from 50 to 6‰. Freshwater acclimation resulted in significant hyponatremia, hypochloremia and muscle hydration. Branchial ICDH activity was lowest in a 12‰ environment and highest at salinity extremes. Renal Na+-K+-ATPase exhibited lower activity in 12 and 6‰ and was markedly elevated in 0‰. Enzyme activities of both liver and kidney indicated elevated gluconeogenic activity in freshwater-adapted fish. Total intestinal Na+-K+-ATPase activity tended to decline in lower salinities; however, lowest activity was found in fish adapted to 12‰. Na+-K+-ATPase activities in different segments of the intestine may reflect the osmoregulatory role of this organ in varying salinities. The data indicated efficient homeostatic control in Mylio macrocephalus acclimated from hypersaline to freshwater environments and clearly demonstrates the haloplasticity of this marine fish species. J. Exp. Zool. 283:226–241, 1999.

Thyroid hormones in cyclostomes and fish and their role in regulation of intermediary metabolism

1. Experimental data obtained in cyclostomes and fish concerning the plasma levels of thyroxine and tri-iodothyronine as well as their influence on intermediary metabolism of lipids, carbohydrates, and proteins are reviewed. 2. The information dealing with the physiological role of thyroid hormones in regulation of metabolic processes seems to be scarce in cyclostomes and controversial in fishes. 3. Nevertheless, the data covered in the review support the generalization that thyroid hormones, probably along with some other hormones, exert a regulatory action on the metabolic processes already on the lower stage of the evolution of poikilothermic vertebrates.

Modulation of fish growth hormone levels by salinity, temperature, pollutants and aquaculture related stress: a review

The focus of this review is on the importance and regulation of fish growth hormone (GH), during exposure to stress. Alterations in environmental salinity impose osmoregulatory stress on fish and upon exposure to increased salinities GH has been shown to be important in maintaining hypoosmoregulatory function. Whilst studies mainly on salmonids, demonstrate that GH essentially performs a role as a seawater adapting hormone a clear correlation of elevated GH with growth and isoosmotic salinity exposure has been identified from studies on sparids. Variations in water temperature have been shown to modulate fish GH with the overall consensus of highest levels of GH during the warmer seasons of the year, suggesting an important role for GH during the temperature acclimatization process, but whether this relates to growth is unclear. Environmentally important pollutants, including xenoestrogens and heavy metals have been shown to affect GH mediated mechanisms, in fish, possibly via interference with the GH receptor and/or GH transcription, whereas aquacultural related stressors such as handling, confinement/overcrowding and nutritional stress have also been shown to affect GH levels. In addition the impact of aquacultural related stressors can also pre-dispose fish to disease leading to chronic suppression of GH. Finally, GH has been recently demonstrated to exert an anti-apoptotic effect in fish cells, when exposed to chemical stress, providing evidence that GH can also serve as a protective agent.

Chronic Salinity Adaptation Modulates Hepatic Heat Shock Protein and Insulin-like Growth Factor I Expression in Black Sea Bream

Abstract: Black sea bream (Mylio macrocephalus) hepatic heat shock proteins hsp90, hsp70, and hsp60 were found to be thermally and reversibly inducible as they were elevated 2.0, 3.2, and 2.1 fold, respectively, on acute heat shock and returned to pre-heat-shock levels after a 40-hour recovery period. To establish whether salinity plays a role in regulating heat shock protein (hsp) and insulin-like growth factor-I (IGF-I) expression in a euryhaline marine fish, we adapted groups of juvenile black sea bream to salinities of 50 ppt (hypersaline), 33 ppt (seawater), 12 ppt (isoosmotic), and 6 ppt (hypoosmotic) for 8 months. The lowest levels of hsps were found in fish reared in an isoosmotic salinity and the highest in those adapted to hypersaline and hypoosmotic salinities. Hepatic β-actin messenger RNA abundance remained unchanged in all groups during salinity adaptation, whereas IGF-I mRNA abundance was highest in isoosmotic adapted black sea bream. This study is the first report of an effect of salinity ranging from hypersaline to hypoosmotic on the expression of different hsp forms and IGF-I in fish, and the possible relationship between environmental salinity, hepatic IGF-I expression, and hsp regulation is discussed.

Antibiotic resistance and plasmid profiles of Vibrio isolates from cultured silver sea bream, Sparus sarba

Abstract A total of 51 potential pathogenic vibrios were isolated from moribund silver sea bream (Sparus sarba) collected from fish farms in Hong Kong. Using the API 20E system and the scheme of Alsina and Blanch (1994) , 7 species were identified from all isolates. These species were Vibrio alginolyticus (24 strains), Vibrio vulnificus (12 strains), Vibrio parahaemolyticus (7 strains), Vibrio logei (4 strains), Vibrio pelagius II (2 strains), Vibrio fluvialis (1 strain) and Vibrio meditterranei (1 strain). The three dominant species (V. alginolyticus, V. vulnificus and V. parahaemolyticus) were confirmed to be virulent to sea bream by experimental challenge. All isolates were screened for plasmid DNA by agarose gel electrophoresis and tested for susceptibility to 16 antibiotics by the agar dilution method. Of the 51 isolates examined, all strains were sensitive to ceftriaxone, streptomycin, nalidixic acid and rifampicin, and almost all were sensitive to ceftazidime, netilimicin, chloramphenicol and sulfamethoxazole. Most isolates were resistant to ampicillin (60.8%), cefuroxime (66.7%), amikacin (55%), kanamycin (58.8%) and trimethoprim (76.5%). Fifteen of the 51 isolates harboured 1–4 plasmids, with sizes ranging from 9 to 123 kb. Both the plasmids and the associated antibiotic resistance (ampicillin, cefuroxime and trimethoprim) of 9 isolates could be transferred to a recipient by single-step conjugation. However, the frequencies were very low, ranging from 10−11 to 10−9. The present results indicate that resistance to these antibiotics is chromosomal.

Endocrine control of nutrition in cyclostomes and fish

Abstract 1. 1. The relationship between nutritional patterns and physiological levels of endogenous hormones, in some species of cytosomes and fish, is studied. 2. 2. Most of the observations are related to species showing a marked life cycle, including natural fasting periods and migrations. 3. 3. Insulin seems to play a major role in regulating the nutritional metabolism, which appears to be largely dependent on gluconeogenesis and on amino acids supply.

Ontogeny of thyroid hormones, cortisol, hsp70 and hsp90 during silver sea bream larval development

We studied the profiles of silver sea bream (Sparus sarba) thyroxine (T(4)), triiodothyronine (T(3)), cortisol and the heat shock protein (hsp) families hsp70 and hsp90 during larval development. Eggs from sexually mature female sea bream were fertilized and larvae were collected at incremental time intervals between 1-46 days post hatch (dph). Both T(4) and T(3) were detected in 1 dph larvae and it was found that both increased as development progressed with a distinct surge in amounts between 21-35 dph, a time associated with direct development of larvae to juveniles. Cortisol increased from 1 dph reaching a maximum and constant level from 35 dph onwards. Using RT-PCR coupled with radioisotope hybridization of immobilized cDNA we assessed the transcript levels of hsp70 and it was found that transcript remained unaltered between 1-14 dph before progressively increasing. Immunoblotting was used to study the larval concentrations of hsp70 and hsp90 and it was found that hsp70 was not significantly changed between 1-14 dph whereas hsp90 increased from 1 dph onwards. These findings suggest an important role for hsp90 in the corticosteroid receptor complex during silver sea bream larval development.

Advances and perspectives on the regulation and expression of piscine heat shock proteins

The focus of this review is on the regulation and expression of heat shock proteins (HSPs), in fish. Within the past decade, molecular studies pertaining to the isolation and characterization of fish HSP genes have been rapidly expanding with many gene sequences from many fish species being reported. Most of the gene sequences presently available belong to the HSP70 family but genes encoding constitutive and inducible members of the HSP90 family have also been identified as well as genes encoding HSP60, HSP47 and small HSP families. Environmental stressors such as alterations in environmental salinity, disease and chemical exposure are known to alter HSP expression and the regulation of HSPs by hormones has received much attention recently. Heat shock proteins are known to play key roles during embryonic development and recent findings have defined their ontogenetic profiles following hatching. Finally, we are gradually starting to add to our understanding as to the transcriptional regulation of HSPs especially the role and importance of the heat shock factor (HSF).

Hormonal status and phagocytic activity in sea bream infected with vibriosis.

Serum taken from female, sexually mature, silver sea bream (Sparus sarba) displaying either no symptoms of vibriosis, mild infection, severe infection or moribundity were assayed for a number of key hormones. Serum cortisol levels were not significantly different among symptomless, mildly- and severely-infected groups, whereas moribund fish displayed hypercortisolemia with a 14-fold increase in serum cortisol in comparison to symptomless fish. Serum estradiol levels were significantly reduced 19-fold in mildly-infected fish and remained at a low level as infection progressed, whereas serum testosterone increased gradually during vibriosis with a 1.8-fold increase in moribund groups in comparison to symptomless groups. Both serum thyroxine (T(4)) and triiodothyronine (T(3)) gradually decreased during vibriosis being 26- and 2.8-fold lower, respectively, in moribund fish in comparison to symptomless fish. The non-specific immune response, as determined by phagocytic activity, was also assessed using macrophages isolated from the pronephros and spleen of infected fish. Phagocytic indices significantly increased in mildly- and severely-infected fish and then decreased from these stimulated levels in moribund fish.