The effect of 3,3′,5-triiodo-L-thyronine and 17-α-methyltestosterone on growth and body composition of the glass stage of the eel (Anguilla anguilla L)

This study was undertaken to determine the influence of orally administered 3,3,5-triiodo-L-thyronine (T₃) or 17--methyltestosterone (MT) on growth and body composition of the eel (Anguilla anguilla L.) during the glass stage.Elvers receiving 20 or 40 ppm of T₃ in the food weighed significantly more (P < 0.05) than controls. However, after 61 days of treatment a dosage of 60 ppm was not efficacious.Terminal percentages of body protein were significantly lower (P < 0.05) in elvers that received 20 ppm or 40 ppm T₃ in their diets, than in the control. Crude body fat content was higher (P < 0.05) in elvers receiving 20 ppm (29% fat) or 40 ppm (28% fat), than in the controls (26% fat). Compared to the control, diets containing T₃ at 20 or 40 ppm increased the body glucose concentration.Glass eels fed a diet containing 1 or 10 ppm MT grew significantly more slowly (P < 0.05) than the controls.Total body protein content was higher (P < 0.05), but total body crude fat content was lower (P < 0.05) in elvers fed a diet with 1 or 10 ppm MT compared to the controls. Total body glucose concentration of elvers administered 10 ppm MT was significantly lower (P < 0.05) than that of the control groups.     

Identification and primary structures of eel type I collagen proα1, proα2 and proα3

Many bony fish type I collagens have a characteristic third chain designated as α3(I). However, much less is known about the primary structure and distinction of the proα(I) chains. Their cDNAs were cloned by RT-PCR from the muscle tissue of Japanese eel, Anguilla japonica. Three cDNAs coding for the triple-helical domain of fibrillar collagen were identified as proα1(I), proα2(I) and proα3(I) chains by sequencing selected tryptic peptides isolated from eel type I collagen subunit chains, α1(I), α2(I) and α3(I). Eel proα3(I) had high amino acid sequence identity (81 %) to its proα1(I). The distribution of seven Cys residues in the C-propeptide of proα3(I) was identical to that of proα1(I). There was a third Cys residue at the 1,268th position from the N-terminus in proα1(I), though a supposed Cys residue at the 1,264th position in proα3(I) was replaced by a Ser residue. Similar replacement has been observed in the proα3(I) chains of trout and zebrafish. These combined results suggest that replacement of the Cys residue allows for the identification of fish collagen proα(I) previously not identified as proα3(I).     

How fast can the European eel (Anguilla anguilla) larvae cross the Atlantic Ocean?

The migration duration of European eel ( Anguilla anguilla ) larvae (leptocephali) from the spawning areas in the Sargasso Sea to the European continental shelf remains highly controversial, with estimates varying from 6 months to more than 2 yr. We estimated the fastest migration period and the shortest distance travelled by eel larvae by simulating Lagrangian particles released in the Sargasso Sea and by simulating a range of larval behaviours (fixed-depth drift, vertical diurnal migration and active-depth selection to maximize current velocity). This enabled us to compute (i) a passive drift speed, and (ii) a hypothetic swimming speed needed for European eel larvae to cross the Atlantic in 6 months (i.e., the migration duration estimated from otolith daily growth increments). Our results show that the minimum travel time for an eel larva that is passively drifting was 10 months and 3 days. Active behaviours (vertical diurnal migration and rheotaxis) paradoxically increased the migration period. We found that for leptocephali to cross the Atlantic Ocean in 6 months, they would need to swim a minimum of 3.4 body lengths per second for 8200 km. No larvae have been observed with such swimming capabilities. These results provide evidence that leptocephali cannot cross the Atlantic in 6 months.     

The cooperation between the Chinese Bureau of Fisheries and the Norwegian Directorate of fisheries

Activities1994In 1994 Peter Gullestad(Present Director General of Fisheries in Bergen) headed a Norwegian delegationvisiting China.In his presentation of“The N orwegian exp erience in fisheries management and control” - hestressed the fact that overcapacity is“the root of all evil”.He also underlined that it is important not only toset up a legal system for fisheries management but also to establish reliable catch statistics.He further morepointed out that good scientific advice is th…     

What are the drivers of the occurrence of illegal fishing and conservation barriers of sturgeons in the Caspian Sea?

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Aromatase (P450arom) and 11β-hydroxylase (P45011β) genes are differentially expressed during the sex change process of the protogynous rice field eel, monopterus albus

Steroids are known to play a crucial role in gonadal sex differentiation in many non-mammalian vertebrates, but also in the gonadal sex change of hermaphroditic teleosts. We investigated the expression of two genes encoding key steroidogenic enzymes, i.e., cytochrome P450 aromatase (P450arom) and cytochrome P45011β-hydroxylase (P45011β), during the sex change of the protogynous rice field eel, Monopterus albus. Using RT-PCR with degenerate primers, we cloned rice field eel homologous fragments for both genes (rcP450arom and rcP45011β) as indicated by the high level of homology with P450arom and P45011β sequences from various vertebrates. Gonadal expression of rcP450arom and rcP45011β mRNA levels were then assessed during the sex change by semi-quantitative RT-PCR and a real-time RT-PCR. rcP450arom was predominantly expressed in ovary, much less in ovotestis, and barely in testis. Conversely, P45011β was markedly up-regulated at the onset of testicular development. These findings underline that regulation of steroidogenesis is an important process in the sex change of protogynous rice field eel, and they clearly indicate that the concomitant down-regulation of P450arom and up-regulation of P45011β are of pivotal importance to the sex change of this species.     

Analysis of the α-amylase gene sequence and the enzyme activity of Indian rock oyster Saccostrea forskali

Indian rock oyster Saccostrea forskali is an important commercial species in Thailand. In this study, its full-length α-amylase (SfAmy) cDNA nucleotide sequence was investigated. The SfAmy cDNA was 1,689 bp long and contained a 1,563-bp open reading frame encoding 520 amino acid residues, including a 17-amino acid signal peptide. The molecular mass and the estimated isoelectric point (pI) of the deduced mature S. forskali α-amylase (SfAMY) were 55.948 kDa and 6.45, respectively. The deduced protein sequence showed 45–88 % identity to other mollusk AMYs. The molecular weight was confirmed by the weight of the purified native enzyme. The specific activities of crude and purified native enzymes toward 1 % starch were 29.53 and 187.42 U/mg. In addition, the obtained recombinant SfAMY also showed activity in digesting 1 % starch. The specific activities of the crude and purified recombinant proteins were 11.8 and 46 U/mg. Both enzymes showed optimal activity temperature at 40 °C but their optimum pH values were different, 6.0 for the native and 5.0 for the recombinant. The expression of SfAmy examined by RT-PCR showed the highest levels in the digestive gland but none was observed in the adductor muscle.     

Effects of process and/or observation errors on the stock–recruitment curve and the validity of the proportional model as a stock–recruitment relationship

We examined the effects of process and observation errors on the selection of the stock–recruitment relationship (SRR) curve using simulations. When the process and observation errors were added to both spawning stock biomass and recruitment, the results were as follows: (1) When the proportional model was set as the true SRR model, there was a high probability that the Ricker or Beverton and Holt model was selected in response to the errors; (2) When the Ricker or Beverton and Holt model was set as the true SRR model, the proportional model was seldom selected in response to the errors; (3) The proportional SRR model should be accepted as the optimum SRR model for the Pacific stock of Japanese sardine; (4) We should use an SRR model that is constructed from more than two independent variables (spawning stock biomass, environmental factors, etc.) when we discuss management of fisheries resources.     

Daily rhythms of cortisol and glucose and the influence of the light/dark cycle on anaesthesia in Nile tilapia (Oreochromis niloticus): Does the timing of anaesthetic administration affect the stress response?

Although daily variations in drug pharmacokinetics have been reported for a variety of teleost species, the influence of this daily variation on the cortisol response following anaesthesia remains poorly understood. To address this, two experiments were performed. The first experiment described the daily patterns of cortisol and glucose secretion in tilapia (Oreochromis niloticus). The second experiment investigated how the timing of anaesthetic administration (specifically at mid‐light [ML] or at mid‐dark [MD]) affects the induction and recovery times and plasma cortisol and glucose levels of juvenile Nile tilapia exposed to benzocaine, clove oil or tricaine methanesulphonate (MS‐222). The results revealed that the effect on the stress response associated with the moment when anaesthesia took place (ML or MD) varied according to the treatment (p < 0.05). Cortisol levels were significantly higher at ML for MS‐222 (ML = 116.23 ± 25.55; MD = 48.25 ± 22.33 ng/dl) (p < 0.05) and clove oil (ML 59.73 ± 14.27; MD 38.26 ± 12.07 ng/dl) (p < 0.05), whereas no significant differences were found between ML and MD cortisol levels for the control treatment (ML = 72.91 ± 18.42; MD = 64.80 ± 10.68 ng/dl) (p > 0.05) or in the benzocaine‐treated group (ML = 38.7 ± 4.90; MD = 38.60 ± 3.69 ng/dl) (p > 0.05). The highest plasma cortisol level in ML was found in the MS‐222‐treated group. All the tested anaesthetics had similar cortisol levels at MD (p > 0.05).     

Structural and functional effects of early exposure to estradiol-17β and 17α-ethynylestradiol on the gonads of the gonochoristic teleost Dicentrarchus labrax

This study investigated the effects of estrogens on sexual differentiation in sea bass (Dicentrarchus labrax L.), a gonochoristic marine teleost that under culture conditions has a histologically sexual undifferentiated period that covers most of the first year of life, after which most individuals develop as males. Sea bass that had no noticeable histological sign of sex differentiation were fed estrogens at two doses (5 or 10 mg kg^-1 food) and for different periods ranging from 48 to 426 days post fertilization (DPF). Exposure to the synthetic estrogen 17-ethynylestradiol (EE₂) at 10 mg kg^-1 food from 60 to 260 DPF, including the sensitive period to equivalent doses of synthetic androgens previously determined for this species (126-226 DPF), significantly (p < 0.05) more than doubled the number of juvenile females to 80%, compared to the control value of 33%, and completely suppressed gonadal development in the remaining 20% of the population. This suggests that the period during which sea bass gonads exhibit high sensitivity to androgens is also very sensitive to estrogens. A comparable exposure to the natural estrogen estradiol-17 (E₂) resulted in 13% of the fish having suppressed gonadal development, but induced 57% of the fish to develop gonads with germinal tissue of both sexes, suggesting a pivotal role for E₂ during this sensitive period. Earlier exposure to EE₂ at 10 mg kg^-1 food from 48-88 DPF, significantly (p < 0.05) increased the number of females to 62% from 36% in the control group, allowing for the normal testicular development in the remaining fish. In contrast, a later chronic exposure (226-426 DPF) to E₂, at either 5 or 10 mg kg^-1 food, starting when the gonads showed no sign of sexual differentiation but past the critical sensitive period, had no effect on the resulting overall sex ratios, indicating that after this period responsiveness of the gonads to estrogens decreases as gonadal sexual differentiation progresses. However, the consequences of this apparently innocuous exposure were later manifested in adults, exemplified by a significant dose-dependent reduction in the number of mature males at 626 DPF, coinciding with the second reproductive season, the time when males normally reach sexual maturation in cultured sea bass. This suggests that chronic exposure to E₂ past the critical sensitive period may not affect the sex ratio, but could result in alterations in the male reproductive organs. This was later verified by histological analysis which revealed a significant (p < 0.05) dose-dependent reduction of the surface of the testicular lobules in the remaining males that did not mature. Together, these experiments illustrate both readily observable and subtle effects of estrogens on sex proportions, gonadal morphology and maturation rates, providing evidence that estrogen exposure can have delayed action in a teleost in a manner similar to the effects described for mammalian species. The possible existence of effects of this latter type in adult fish could be considered when evaluating the consequences of deliberate or accidental exposure to estrogens or putative estrogenic chemicals, particularly if such exposure had taken place during sex differentiation.     

Molecular cloning of the cDNA encoding the β subunit of thyrotropin and regulation of its gene expression by thyroid hormones in the goldfish, Carassius auratus

A cDNA encoding the subunit of thyrotropin (TSH) was isolated from a goldfish (Carassius auratus) pituitary gland cDNA library. By comparing the sequence with other teleost TSHs, a signal peptide of 19 amino acids and a mature hormone of 131 amino acids were predicted for goldfish TSH subunits. The resulting putative mature hormone of 131 amino acids had well-conserved cysteine positions and a putative N-linked glycosylation site; homology was 51–67% with TSHs from other teleosts, 38–43% with tetrapod TSHs, but only 27 and 29% with goldfish GTH-I and -II, respectively. We also examined the effects of thyroid hormones (TH) and thiourea (TU, an inhibitor of TH production) treatments on TSH and GTH subunit gene expressions in the goldfish pituitary gland. After thyroxine (T₄) treatment, circulating T₄ concentration increased and TSH mRNA level decreased. Supressing the amount of circulating T₄ and triiodothyronine (T₃) by TU treatment increased the TSH mRNA level. Moreover, T₄ replacement therapy (simultaneous treatment of both TU and T₄) caused a high level of circulating T₄ and a low level of circulating T₃, and a decrease in the TSH mRNA level. Thus, changing levels of circulating TH exert a negative feedback on the level of TSH subunit mRNA in goldfish in vivo. On the other hand, GTH subunit mRNA levels were not affected by changes in the levels of circulating TH.     

Distribution and movement between habitats with growth of the hard clam Meretrix lusoria in the Shirakawa–Midorikawa estuary of the Ariake Sea

The distribution and movement between habitats with growth of the hard clam Meretrix lusoria were examined by comparing the size–frequency distributions among 17 sites in the Shirakawa–Midorikawa Estuary of the Ariake Sea. This clam is a commercially important bivalve in Japan, and its annual catch is largest in the Ariake Sea. At the study sites, new recruits were abundant at river mouths, and density was strongly affected by the distance from coastal tidal rivers and streams. In contrast, adults were widely distributed on tidal flats, although density was low at many sites. At marine site Oda, the density of adults was higher than that of new recruits at all sites and higher than that of juveniles at most sites. These results indicate that this species moves from riverine sites to marine sites with growth. Moreover, the observed low density of adult clams may indicate overfishing. The active movement of M. lusoria across the fishing grounds complicates the sustainable resource management of this species. Therefore, further studies are needed for effective resource management of M. lusoria.     

Response to “Psychophysics and the Sensory Assessment of Fish”

Fillets from Pacific cod (Gadus macrocephalus) were salted with and without polyphosphates (PP) by means of a short three-step salting process. The changes in phosphate and water content during different steps of production were determined by comparing fillets with and without addition of PP. While fillet samples after salt injection and wet-salting contained different water content, from 80.1% to 74.6% depending on processing step and PP addition or not, after dry-salting there was no significant difference in water content between fillets with (58.1%) or without PP (58.9%). Dry-salted fillets with PP addition showed a phosphate content of 6.1 mg P₂O₅/g. In the following rehydration process (48 h), the total phosphate content dropped down to 2.9 mg P₂O₅/g, which was lower than the natural total phosphate content of 4.4 mg P₂O₅/g in the raw material.     

Decline and fall of the salmon fisheries in the Netherlands: is restocking the Rhine a reality?

Abstract. The Atlantic salmon, Salmo salar L., was once of major importance to the fishing industry along the River Rhine. This paper discusses the Dutch and German salmon catches over the years 1863–1950. Even up to the end of the last century, it was not uncommon for Dutch and German fishermen to land 100000 salmon a year. However, factors such as the increased use of locks and weirs along the Rhine, coupled with growth in pollution, soon led to a rapid decline in numbers. By 1933, the salmon fishing industry in the Netherlands had virtually ceased to exist. Analysis of the available catch statistics suggests that the decline in the salmon population could have started before official records began. Although the degree of scatter in the data and uncertainties in the assumptions preclude the possibility of drawing firm conclusions about the survival rate of salmon, these figures illustrate how difficult it will be to maintain a stable population in the Rhine. Moreover, a number of changes have taken place since the heyday of salmon in western Europe, which could compound the problem. Of particular importance in the context of the Rhine are:

• 1 the closure of two of the major migration routes to the sea (Haringvliet and Zuiderzee);
• 2 morphological changes in the river;
• 3 chemical and thermal pollution;
• 4 the loss of accessible spawning and nursery areas of the required quality;
• 5 the disappearance of salmon from other rivers that flow into the North Sea such as the Rivers Elbe, Weser and Ems. If salmon were only reintroduced into the Rhine, a certain proportion would probably stray and infiltrate these other rivers.

The fact that the impact of these changes is difficult to quantify increases the uncertainty associated with maintaining a stable stock of salmon in the Rhine.     

Do boating and basking mix? The effect of basking disturbances by motorboats on the body temperature and energy budget of the northern map turtle

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Investigation of the Protective Effect of β-carotene in the Prevention of Lipid and Protein Oxidation in Carp Meat during Different Storage Times

ABSTRACT

This study was aimed to investigate the effects of dietary β-carotene supplement for 42 days on lipid and protein oxidation biomarkers in carp meat at different times of storage. Seventy-five fish were divided into three groups: group 1 as control group was fed with basic diet; groups 2 and 3 received 50 and 100 mg kg^?1 diet β-carotene, respectively. Based on the present study results, muscle malondialdehyde concentrations were significantly lower following β-carotene consumption at 0, 24, 72, and 96 h after harvest in group 3 compared to the control group (p < 0/05). Muscle protein carbonyl contents showed a significant decrease following β-carotene supplementation at 0, 48, and 96 h after harvest in group 3 compared to the control group. Ferric reducing antioxidant power values were significantly increased following β-carotene supplementation at 72 and 96 h after harvest in group 3 compared to the control group. The results indicated that β-carotene supplementation with a dose of 100 mg kg^?1 diet is largely effective to improve the oxidative status of carp meat by reducing lipid and protein oxidation.     

Habitat and prey selection of common minke,sei, and Bryde’s whales in mesoscale during summer in the subarctic and transition regions of the western North Pacific

This study represents the first quantitative analysis of the characteristics of the distribution areas and stomach contents of common minke whale Balaenoptera acutorostrata, sei whale B. borealis, and Bryde’s whale B. edeni in relation to oceanographic and prey environments in mid summer in the western North Pacific. Common minke whales were distributed within subarctic regions and the northernmost region of the transitional domain, coinciding with the main habitat of their preferred prey, Pacific saury Cololabis saira. Sei whales were mainly found in the northernmost part of the transition zone and showed prey preference for Japanese anchovy Engraulis japonica, which was significantly more abundant in the main distribution area of the whale than in its adjacent areas. “Hot spots” of Bryde’s whales were found in several regions of the transition zone between the subarctic boundary and the Kuroshio front. This whale species preferred Japanese anchovy as prey, for which the distribution density was significantly higher in the main distribution area of the whale than in the adjacent areas. These results indicate that the summer distributions of Pacific saury and Japanese anchovy greatly influence the distributions of these whale species, suggesting that the whales’ habitat selection is closely related to their prey selection.     

Comparison of 3,5,3′-triiodo-L-thyronine and L-thyroxine absorption from the intestinal lumen of the fasted rainbow trout,Oncorhynchus mykiss

The absorptions of 3,5,3-triiodo-L-thyronine (T₃) and L-thyroxine (T₄) from the intestinal lumen of the rainbow trout were compared in vivo. Tracer doses of [¹²⁵I]T₄ (⁺T₄) or [¹²⁵I]T₃ (^*T₃) were injected through an anal cannula into the duodenum of trout fasted for 3 days at 12°C, and radioactivity was measured in blood and tissues at 4–48 h. ^*T₃ was removed more extensively than ^*T₄ from the intestinal lumen and more radioactivity was absorbed into the blood and tissues of u+T₃-injected trout than ^*T₄-injected trout. HPLC analysis showed that a high proportion of the radioactivity in the plasma, liver, kidney and intestinal lumen of ^*T₃-injected trout remained as the parent ^*T₃. However, in ^*T₄-injected trout most plasma radioactivity was in the form of ¹²⁵I^–, and by 24 h a high proportion of luminal radioactivity was ¹²⁵I^–. By 48 h, over 4% of the injected ^*T₃ and 1% of the injected ^*T₄ dose resided in the gall bladder, primarily as derivatives of ^*T₃ or ^*T₄. We conclude that T₃ is absorbed more effectively than T₄ from the intestinal lumen of fasted trout, indicating the potential for an enterohepatic T₃ cycle.