Antifreeze proteins in the urine of marine fish

Several species of marine teleosts have evolved blood plasma antifreeze polypeptides which enable them to survive in ice-laden seawater. Four distinct antifreeze protein classes differing in carbohydrate content, amino acid composition, protein sequence and secondary structure are currently known. Although all of these antifreezes are relatively small (2.6–33 kd) it was generally thought that they were excluded from the urine by a variety of glomerular mechanisms. In the present study antifreeze polypeptides were found in the bladder urine of winter flounder (Pseudopleuronectes americanus), sea raven (Hemitripterus americanus), ocean pout (Macrozoarces americanus) and Atlantic cod (Gadus morhua). Since the plasma of each of these fish contains a different antifreeze class it would appear that all four classes of antifreeze can enter the urine. The major antifreeze components in the urine of winter flounder were found to be identical to the major plasma components in terms of high performance liquid chromatography retention times and amino acid composition. It is concluded that plasma antifreeze peptides need not be chemically modified before they can enter the urine.     

Relationship between metabolic rate in vitro and body mass in a marine teleost,porgy Pagrus major

The rate of oxygen consumption of minced whole body was determined volumetrically, as an indication of metabolic rate in vitro (M _{in vitro} ), at 20°C in porgy Pagrus major ranging from 0.0002 g (just after hatch) to 2.9 g (67 days old) in body mass. A triphasic relationship was found between M _{in vitro} of individual fish (l.min^–1) and wet body mass W (g). During the prolarval stage accompanied with the transitional period to the postlarval stage (0.00020–0.00023 g, 0–6 days old), the mass-specific metabolic rate in vitro (M _{in vitro} /W in l.g^–1.min^–1) increased with age (D in days) as expressed by an equation M _{in vitro} /W = 3.88 + 0.74/D. During the postlarval stage (0.00031–0.003 g, 8–22 days old), M _{in vitro} /W remained almost constant, independent of body mass following an equation M _{in vitro} /W = 5.24 W^–0.085. During the juvenile and adolescent stages (0.0047–2.9 g, 30–67 days old), M _{in vitro} /W decreased with increasing body mass following an equation M _{in vitro} /W = 1.66 W^–0.235. These results correspond with the triphasic relationship between metabolism in vivo and body mass observed in intact porgy of 0.0002–270 g (Oikawa et al. 1991). It is concluded, therefore, that the dependence of mass-specific metabolic rate on body size exists in vitro as well as in vivo, during the early stages in the porgy. Based on these results, factors controlling the metabolism-size relationship are discussed.     

Influence of the gametogenic cycle on the biochemical composition of the ovary of the great scallop

The oogenic cycle and biochemical composition of the ovary of raft-cultured great scallop (Pecten maximus) were studied during the period April 1990–July 1991. The ovary condition index (FGI) and stereological studies showed the existence of two principal spawning periods, winter and late spring-early summer. No sexual resting period was found. Oocyte lysis was high throughout the year. Ovarian lipid levels displayed a clear seasonal pattern linked to the gametogenic cycle. Total lipid (TL, 16–21% dry weight), acylglycerol (AG, 20–65% TL) and free sterol (FS, 2.8–6.4% TL) levels were, generally, higher in the ripe ovary and a decrease coincided with spawning. Protein (59–63% dry weight), glycogen (<3% dry weight) and phospholipid (PL, 26–35% TL) levels showed no clear seasonal trend. The TL and AG were a good index of ovarian sexual maturity. The TL % of dry weight) correlated well with the female gonad condition index (r _s = 0.779, p < 0.001), and AG (% f TL) correlated well with the mean oocyte diameter (r _s = 0.630, p < 0.01) and the female gonad condition index (r _s = 0.443, p < 0.05).     

Rates of oxygen consumption and ammonia excretion of juvenile Eurasian perch Perca fluviatilis L.

The impact of feeding, fish size (body weight from 18.5 to 56.5 g) and water temperature (20 and 23 °C) on oxygen consumption (OC, mg O₂ kg^–1 h^–1) and ammonia excretion (AE, mg TAN kg^–1 h^–1) was studied in Eurasian perch held in recirculation systems. OC for both fed and feed-deprived (3 days) fish was higher at 23 °C (278.5 and 150.1 mg O₂ kg^–1 h^–1) than at 20 °C (249.3 and 135.0 mg O₂ kg^–1 h^–1; P < 0.01). AEs for both fed and feed-deprived fish were also significantly higher at 23 °C than at 20 °C (P < 0.001). Water temperature and fish size had a significant impact on the oxygen:feed ratio (OFR, kg O₂ kg^–1 feed fed day^–1) and ammonia:feed ratio (AFR, kg TAN kg^–1 feed fed day^–1; P < 0.001). Their average values at temperatures of 20 and 23 °C were 0.17 and 0.19 kg O₂ kg^–1 feed fed day^–1 and 0.009 and 0.011 kg TAN kg^–1 feed fed day^–1, respectively.     

An assessment of the west winter–spring cohort of neon flying squid (Ommastrephes bartramii) in the Northwest Pacific Ocean

In the Northwest Pacific, the squid jigging fisheries targeted the west winter–spring cohort of neon flying squid (Ommastrephes bartramii) from August to November. Total annual catch by the Chinese mainland squid jigging fleet during 2000–2005 ranged from 64,100 to 104,200 t. The unique life history of this squid species makes the use of traditional age- or length-structured models difficult in evaluating the effect of intensive commercial jigging on this stock. We fitted a modified depletion model to the Chinese jigging fisheries data to estimate the squid stock abundance during 2000–2005. Monthly biological data were randomly sampled from the five squid jigging vessels during the fishing seasons. Effects of using different natural mortality rates (M) and three different error assumptions were evaluated in fitting the depletion model. Based on sensitivity analyses, the log-normal error model was found to be preferred for the squid assessment. The assessment results indicated that the initial (pre-fishing season) annual population sizes ranged from 199 to 704 million squid with the M value of 0.03–0.10 during 2000–2005. The proportional escapement (M = 0.03–0.10) for different fishing seasons over the time period of 2000–2005 ranged from 15.3% (in 2000) to 69.9% (in 2001), with an average of 37.18%, which was close to the management target of 40%. Thus, the current fishing mortality of the squid jigging fishery was considered to be sustainable. We inferred its annual maximum allowable catch ranging from 80,000 to 100,000 t. This study suggests that the modified depletion model provides an alternative method for assessing short-lived species such as O. bartramii.     

Age and growth of the largemouth perch Percichthys colhuapiensis in the Negro river, Argentine Patagonia

Largemouth perch (Percichthys colhuapiensis) represents one of the most economically important fish species in the Argentine Patagonia. However, little research has been done on the age and growth and population dynamics of this fish, though both studies are essential to properly deal with fisheries forecasts and management. As a contribution to elaborating management programmes for P. colhuapiensis, we evaluated the age and growth of this species in the Negro river via scale and whole otolith reading methods. The sample consisted of 579 specimens ranging in total length (TL) from 90 to 475 mm, captured seasonally from December 1994 to December 1995. The formation of scale annuli (end of winter) and the hyaline zone on otoliths (winter) of adult fish coincided with the beginning of the spawning season (end of winter-beginning of spring). The maximum estimated age was 11 years, which indicates that this is a relatively long-lived species. Otoliths were useful for ageing specimens 1–5 years-old, but above this age whole otoliths yielded lower age estimates than scales. Isometric growth of weight with length was found for total population, juveniles, and separate sexes (p > 0.25 in all cases). No significant differences between the length–weight relationships of sexes were observed (p > 0.10). Length at first maturity was significantly higher for males (TL₅₀ = 271 mm TL; r = 0.88) than for females (TL₅₀ = 243 mm TL; r = 0.96) (p < 0.01). Largemouth perch exhibited a consistent pattern of increase in length with age, with a period of fast growth during the first 5 years, and a slow-growing phase during the rest of his life. The growth parameters based on scale data were L∞: 462.1 mm, k = 0.23 and t₀ = −0.94 for total population, L∞: 402.3 mm, k = 0.33 and t₀ = −0.67 for males, and L∞: 548.4 mm, k = 0.15 and t₀ = −1.59 for females, whereas those based on otolith reading were L∞: 537.4 mm, k = 0.17 and t₀ = −1.0 for total population, L∞: 497.6 mm, k = 0.21 and t₀ = −0.79 for males, and L∞: 582.0 mm, k = 0.14 and t₀ = −1.53 for females. Scales are concluded to be the best structure to age P. colhuapiensis because they rendered L∞ values closer to the maximum TL observed, high precision, easiness of collection, low processing time, and the possibility of performing non-destructive monitoring studies.     

Growth and feed utilisation of rainbow trout subjected to changes in feed lipid concentrations

Rainbow trout Oncorhynchus mykiss grew from 44 to 326 g in 96days when held at 12 °C. Fish were fed to satiation twice dailywith either high (L₁: 30.8%, L₂:31.4%) or lower-lipid feeds (C₁: 18.8%,C₂: 21.8%). Four feeding treatments were studied.Group C₁C₂ received feed C₁ for 43 days(days 0–43) and C₂ thereafter (days 44–96).Groups L₁L₂, L₁C₂ andC₁L₂ were subjected to dietary changes asindicated by the feed designations. After a short period of feedadaptation, fish ingested similar amounts of feed energy i.e., they ateless by weight of the lipid-rich (L) feeds. Feed lipid content did notaffect growth but fish fed L-feed had reduced feed conversion ratio(FCR) compared to fish fed C-feed (0.731 vs. 0.773) during days0–43 (P < 0.01). After 96 days,L₁L₂-fish were lower in body protein(15.8%) than the C₁C₂-fish (16.8%)(P < 0.01). L-feeds also tended to increase percentage lipidand reduce percentage whole body moisture and ash. A higher net proteinutilisation (NPU) was recorded in fish fed L-feeds (43.6%)compared to fish fed C-feeds (38.8%) in days 0–43(P < 0.05). This seemed to be the result of a lower proteinintake rather than a protein-sparing effect of feed lipid. Above athreshold value of approximately 6.5 mg protein eaten·g bodywt_{minus 1}·day_–1, NPU decreased.     

Long-term separate and combined effects of environmental hypercapnia and hyperoxia in Atlantic salmon (Salmo salar L.) smolts

Atlantic salmon (Salmo salar L.) parr (mean start weight 50 g) were reared in freshwater (FW) and exposed to three levels of oxygen saturation measured in effluent water; control group (93% O₂, LO₂), medium (111% O₂, MO₂) and high (123% O₂, HO₂). Further three groups were exposed to similar water oxygen levels in combination with elevated carbon dioxide levels (17–18 mg L^– 1 CO₂), named LO₂–CO₂, MO₂–CO₂ and HO₂–CO₂, respectively. The experiment was run in duplicate tanks for 42 days, and the fish were subsequently transferred to the same seawater (SW) regime for 45 days for an assessment of post-smolt growth. As a consequence of the CO₂ addition, tank pH levels in the FW period were reduced from 6.7 to 5.9 for the hypercapnia groups compared to for the normcapnia groups. Water temperature in FW ranged between 6.4 and 9.0 °C. Citrate was added to the water to complex labile aluminium.In the CO₂ groups observed ventilation frequencies were significantly increased compared to the control (p < 0.05). This difference declined towards the end of the FW period, suggesting acclimation to elevated CO₂. The degree of oxygenation appeared to contribute to the acclimation as the lowest mean ventilation frequency on day 36 was found in the HO₂–CO₂ group and the highest in the LO₂–CO₂ group. Lower plasma chloride and sodium levels were observed in the CO₂ groups relative to the respective oxygenation groups during the FW period, while plasma chloride and sodium levels were normalised to equal levels for all groups after 44 days in SW. No significant differences were found among treatments for blood concentrations of red blood cells, haemoglobin, potassium and glucose during the experiment.By termination of the FW period, the HO₂ group had significantly higher body weight than all other groups (p < 0.05), with specific growth rate significantly higher than the CO₂ groups (p < 0.05). Further, the condition factor was significantly lower in all the CO₂ groups at the end of the FW period compared to the control and normcapnia groups (p < 0.05). Although variable among replicates, occurrence of nephrocalcinosis was 10 times higher in the hypercapnia groups than in the control and normcapnia groups. Mortality was negligible (< 2.0%) during the trial, and most of the mortality occurred following SW transfer.     

Population ecology parameters and biomass of golden grey mullet (Liza aurata) in Iranian waters of the Caspian Sea

This paper examines the changes in the population ecology parameters and biomass of golden grey mullet (Liza aurata) in Iranian waters of the Caspian Sea from 1991 to 2005. For most years during this 14-year period, we estimated the age structure of the catch, length–weight relationship, von Bertalanffy growth parameters, condition factor, natural and fishing mortality and biomass. Growth parameters were estimated as L_∞ = 62.7 cm, K = 0.15 year⁻¹, t₀ = −0.23 year⁻¹. The instantaneous coefficient of natural mortality was estimated as 0.350 year⁻¹ and the instantaneous coefficient of fishing mortality varied during the 14-year period between 0.111 to 0.539 year⁻¹. Biomass estimates of golden grey mullet, from the biomass-based cohort analysis were increased from 13,527 mt in 1991–1992 to 23,992 mt in 2002–2003. In 2004–2005, it was estimated to be 23,658 mt. We concluded that at the present time, the stock of golden grey mullet is not being over-fished.     

Osmoregulation in the mudskipper,Boleophthalmus boddaerti II. transepithelial potential and hormonal control

Boleophthalmus boddaerti submerged in 10%, 50% and 80% seawater (sw) for 7 days, had whole body transepithelial potentials (TEP) of 3.3, 18.3 and 22.9 mV, respectively. Hypophysectomy significantly decreased the TEP ofB. boddaerti and reversed the polarity of the TEP of the fish exposed to 10% sw.Hypophysectomy also significantly decreased the branchial Na⁺-K⁺ activated adenosine triphosphatase (Na⁺,K⁺-ATPase) activity but increased the activity of branchial HCO₃ ^–-Cl^– stimulated adenosine triphosphatase (HCO₃ ^–,Cl^–-ATPase) inB. boddaerti exposed to 10% sw. However, survival in 10% sw was not significantly impaired by hypophysectomy and no significant change in plasma osmolality and plasma Na⁺ and Cl^– concentrations was observed.Various doses of ovine-prolactin or salmon-prolactin were unable to restore the TEP of hypophysectomizedB. boddaerti in 10% sw to that of the sham-operated fish. However, cortisol increased TEP to a positive value in hypophysectomizedB. boddaerti, though it was still lower than the sham-operated control. Cortisol treatment also affected the plasma osmolality, plasma Na⁺ and Cl^– contents and branchial Na⁺,K⁺-ATPase and HCO₃ ^–,Cl^–-ATPase activities. Overall, the hormonal control of osmoregulation inB. boddaerti appeared to differ from that of other teleosts.     

Isolation and partial characterization of a novel keratan sulfate proteoglycan from metamorphosing bonefish (Albula) larvae

Proteoglycans (PGs) were isolated from leptocephalous larvae of the bonefish (Albula sp.), which were in the early stages of metamorphosis, using both associative and dissociative conditions in the presence of protease inhibitors. The procedure was rapid and resulted in an extraction efficiency of 75% (associative) and 85–90% (dissociative). The majority of co-extracted protein could be effectively separated from the PGs by utilizing either Sepharose CL-2B or CL-6B gel chromatography. Sepharose CL-2B chromatography of extracted PGs after treatment with bacterial keratan sulfate-endo--galactosidase (keratanase) showed that most of the high molecular weight (M _r) carbohydrate was degraded. Free keratan sulfate (KS) chains were prepared from whole-larva extracts (which also contain small amounts of chondroitin sulfate) by both chondroitinase ABC treatment and ethanol fractionation. Sepharose CL-6B chromatography under dissociative conditions showed that larval KS chains were much larger (M _r55,000) than those from cornea. These chains tended to aggregate when chromatographed under associative conditions. Larval KS was degraded by keratanase and resistant to chondroitinase, ABC and testicular hyaluronidase. Differences were also noted in the oligosaccharides produced by keratanase treatment of the two preparations. However, biochemical composition of larval and corneal KS was similar.Abbreviations KS keratan sulfate - CS chondroitin sulfate - Gal galactose - GlcN glucosamine - GlcNAc N-acetylglucosamine - EDTA ethylenediaminetetraacetic acid - PG proteoglycan - GAG glycosaminoglycan - SDS sodium dodecyl sulfate - PAGE polyacrylamide-gel electrophoresis - TLC thin-layer chromatography - V _o void volume - V _t total volume - M _r molecular weight - U units     

Oxygen consumption and responses to hypoxia of ammocoetes of the southern hemisphere lampreyGeotria australis

The standard rate of oxygen consumption of ammocoetes (larvae) ofGeotria australis with a mean weight of c. 0.5 g was 9.6, 31.4 and 59.4l g^–1 h^–1 at 4.5, 15.5 and 25.0°C respectively, which gives an overall Q₁₀ of 2.4. The regression coefficient for the logarithmic relationship between oxygen consumption and body weight at 15.5°C was 0.704. The ammocoetes ofG. australis have a much lower rate of oxygen consumption at 15.5 and 25.0°C than those of holarctic lampreys. This presumably reflects the lower oxygen delivery pressure to their tissues and helps account for their slow growth rate. At 15.5°C, ammocoetes ofG. australis emerged from the substrate at 21–25 mm Hg and, unlike those of the Northern HemisphereIchthyomyzon greeleyi, died at 14–17 mm Hg. Thus, despite having a thinner water/blood barrier in the gills and blood with a higher oxygen affinity and capacity than holarctic ammocoetes, the larvae ofG. australis cannot survive very low dissolved oxygen tensions. This is apparently related to an inability of larvalG. australis to meet the high oxygen requirements of the respiratory pump at these oxygen tensions. During metamorphosis, oxygen consumption at 15.5°C rose from approximately 27l g^–1 h^–1 at the beginning of transformation to 33.2l g^–1 h^–1 by Stage 3 and then rapidly to 66l g^–1 h^–1 at Stage 6. It remained near this level in Stage 7 and the downstream migrant.     

Effect of triiodothyronine on the growth and survival of larval striped bass (Morone saxatilis)

This study was carried out to test the effect of triiodothyronine (T₃) on the growth and survival of larval striped bass (Morone saxatilis). Growth and survival of striped bass held in 5 ppt seawater and treated with various doses of T₃ were measured beginning at 5 and 16 days after hatching. Body content of T₃ was measured by radioimmunoassay. T₃ dissolved in the 5 ppt seawater was taken up by larval striped bass in a dose-dependent manner, and affected the growth and survival of the fish. At 5 days after hatching, T₃ at 100 ng ml^–1 and 50 ng ml^–1 retarded the growth of larval striped bass and caused a lower survival rate than T₃ at 25 ng ml^–1 or the control treatment. At 16 days after hatching, T₃ at 100 ng ml^–1 retarded the growth of larval fish and caused a higher mortality. T₃ at 10 ng ml^–1 and 1 ng ml^–1 did not show any effect on either survival or growth. Body content of T₃ returns to control levels within days following end of treatment. The results indicate that exogenous T₃ can be detrimental to the growth and survival of larval striped bass.     

Determination of dosage of Azotobacter and organic fertilizer for optimum nutrient release, net primary productivity and fish growth in fresh water fish ponds

Four experiments were conducted in order to determine the optimum dosageof Azotobacter chroococcum vis-a-vis organic fertilizer(cow-dung) required for optimum pond productivity. Hydrobiological parameters ofpond water, Azotobacter survival (viable counts), netprimary productivity (NPP) and fish growth were monitored. Studies have revealedthat irrespective of the treatments, dissolved oxygen (DO) levels weresignificantly (P < 0.05) lowered on inoculating the ponds withAzotobacter. Alkalinity, O-PO₄,NO₃-N, turbidity, NPP, plankton population and fish growth weresignificantly (P < 0.05) enhanced in ponds inoculated withAzotobacter @ 100.0 ml pond^–1w^–2 in combination with cow-dung @ 10000 kgha^–1 y^–1. At higher or lower dosages offertilizers, the values in most of these parameters remained low. On the otherhand, total kjeldahl nitrogen and NH₄-N increased continuously. Ingeneral, viable bacterial counts decreased with increase in pH, however, therate of nitrogen fixation was not affected. Multivariate analysis of the data revealed a significantpositive correlation of nutrients (Total kjeldahl Nitrogen, NO₃-N andO-PO₄), with NPP and plankton populations. NH₄-N, however,showed a significant negative correlation with DO, NPP and plankton populations.Highest fish biomass and SGR also coincided with the highest NPP and planktonpopulations, revealing that a dose of 100.0 ml pond^–1w^–2 (for 25 m³ ponds) ofAzotobacter along with 10000 kg ha^–1y^–1 of cow-dung appears to be optimum for obtainingoptimum pond productivity and fish yield. Nutrients in the sediment(NO₃-N and O-PO₄) also followed similar trend. On theother hand, organic carbon increased continuously with each increase in thedosage of fertilizers. A decline in fish biomass and pond productivity at higherfertilizer dosages has been attributed to low DO, high NH₄-N and BOD.     

Demonstration of putative membrane and cytosol steroid receptors for 17α, 20β-dihydroxy-4-pregnen-3-one in brook troutSalvelinus fontinalis oocytes by photoaffinity labelling using synthetic progestin 17,21-dimethyl-19-nor-pregn-4,9-diene-3,20-dione (R5020)

Cytosol from brook trout ovarian follicles (stages 1–3) was photoaffinity (PA) labelled using synthetic progestin 17,21-dimethyl-19-nor-pregn-4,9-diene-3,20-dione ([³H]R5020). The covalently bound cytosol protein had a relative mass of 501,000 M_r following Sephacryl S-300 column chromatography. The zona radiata membrane fraction from brook trout oocytes which had gone through the first phase of meiotic maturation (stages 6–7) was isolated by ultracentrifugation of the whole oocytes. The zona radiata solubilized protein presumably from the oocyte membrane was also PA labelled and found to give a peak at 355,000 M_r. The SDS PAGE of the cytosol and zona radiata PA labelled protein gave very similar subunits indicating that the membrane protein and the cytosol protein, both of which bind the maturation inducing steroid (MIS) 17,20-dihydroxy-4-pregnen-3-one (17,20-DHP), have similar subunit structures. The isolated zona radiata protein showed cooperativity of binding to [³H]17,20-DHP and PA labelling to [³H]R5020. The association constant (K_a) was 2.0×10⁷M^–1 and maximum binding capacity (N_max) 427 fmoles/mg protein with MIS [³H]17,20-DHP.No evidence for nuclear binding of MIS [³H]17,20-DHP or PA labelling of [³H]R5020 to nuclei was observed. The nuclei were isolated from stages 1 and 3 fresh ovarian follicles of brook trout. The experimental evidence presented demonstrates the presence of MIS 17,20-DHP receptor-like protein from the zona radiata membranes by PA labelling in brook trout oocytes during final stages of maturation.     

Growth and production of the Amazonian tambaqui in fixed cages under different feeding regimes

Experimental culture of the native Amazonian fish tambaqui, Colossoma macropomum, in fixed cages was carried out over a period of 8 months, in Lake Urubu (Rio Grande do Norte, Brazil), to assess the viability of fixed cage culture of tambaqui and to test the influence of diet on growth rates. Nine synthetic net cages (1 m³) were each stocked with 45-day-old fish (mean weight 3 g; mean total body length 51 mm) at a density of 34 fry m^–3. During the first 2 months of culture, fish were fed a balanced formulated feed on an as-fed basis at the rate of 5% body weight day^–1. During months 3–8 this continued for fish in treatment 1 while those in treatment 2 were fed tropical regional fruits, on a wet weight basis at the rate of 5% body wt day^–1. Fish in treatment 3 were given no supplementary feed. Monthly biometric measurements were made on all fish. Fixed cage fish culture was shown to be a viable and simple technique. Survival in all treatments was 100%. With balanced supplementary feed, production was 14.4 kg m^–3, compared with 4.9 kg m^–3 and 2.1 kg m^–3, respectively, in the treatments where fish were fed with fruits and were not given any supplementary feed.     

Demographic analysis of the night shark (Carcharhinus signatus, Poey, 1868) in the equatorial Southwestern Atlantic Ocean

A demographic analysis of the night shark (Carcharhinus signatus) was carried out to establish the conservation status of this species caught by longlines on oceanic banks off northeastern Brazil. The biological input parameters (age at first maturity, longevity, fecundity and natural mortality) used for the construction of life tables were taken randomly from their respective probability distributions, taking into account the uncertainty of the parameter estimates by employing Monte Carlo simulations. Nine scenarios were generated from natural (M), total (Z), initial (Z₀—corresponding to the first year of life of the cohort) and population equilibrium (Z′) mortality rates. Each scenario was executed 1000 times, varying the vital input rates for the estimation of the demographic parameters (net reproductive rate, R₀; mean generation length, G; and intrinsic rate of population increase, r). Age at first maturity for C. signatus is 10 years; 89.2% of the stock is made up of juveniles, with fishery recruitment beginning at 5 years of age. The scenarios reveal that catches prior to first sexual maturity result in a significant reduction in population (−8.1%/year) and that the population would only support current efforts if the individuals caught are over 10 years of age or if mortality due to fishing efforts corresponded to the equilibrium rate beginning with recruitment at 5 years of age. A low survival rate is estimated for the first year of life. In order for the population to remain in equilibrium with current mortality rates and recruitment age, survival should be around 0.9. The combination of a low initial survival rate, low fecundity, fishery efforts and the large number of juveniles caught indicates that the C. signatus population off northeastern Brazil is being overexploited.     

Acute Toxicity of Synthetic Pyrethroid Cypermethrin on the Common Carp (<Emphasis Type="Italic">Cyprinus carpio</Emphasis> L.) Embryos and Larvae

In this study, the toxic effects on the embryos and larvae of the common carp were used as a model to investigate the synthetic pyrethroid pesticide, cypermethrin, which contaminates aquatic ecosystems. Data obtained from the cypermethrin acute toxicity tests were evaluated using the Probit Analysis Statistical Method. The control and eight test experiments were repeated five times. The number of dead embryos significantly increased in response to cypermethrin concentrations 0.0001, 0.001, 0.01, 0.1, 1, 2, 4 and 8 μg l⁻¹ (p<0.05 for each case). The 48 h LC₅₀ value (with 95% confidence limits) of cypermethrin for common carp embryos was estimated at 0.909 (0.256–5.074) μg l⁻¹. Dose–response decreases in hatching success were recorded as 87.4, 85.0, 80.2, 71.4, 56.3, 48.6, 38.8 and 23.5%, respectively. The lowest concentration of cypermethrin (0.0001 μg l⁻¹) produced a significant increase in the number of dead larvae compared to the control group (p<0.05). The number of dead larvae significantly increased with increasing cypermethrin concentrations exposed for 1–96 h (p<0.05). The highest concentration (8 μg l⁻¹) showed the highest larvae mortality. The 96 h LC₅₀ value (with 95% confidence limits) of cypermethrin for common carp larvae was estimated at 0.809 (0.530–1.308) μg l⁻¹. The results of the study suggest that low levels of cypermethrin in the aquatic environment may have a significant effect on the reproduction and development of carp.     

Growth and food intake models in Octopus vulgaris Cuvier (1797): influence of body weight, temperature, sex and diet

Multiple regression analysis was used to develop mathematical models applicable to the growth and food intake of Octopus vulgaris. The variables considered were: body weight (Bw: 175–3,500 g), temperature (T: 13–28 °C), sex (S: male = 0, female = 1) and diet (D: bogue fish = 0, crabs = 1). Growth and food intake may be succesfully expressed by means of the following equations: Ln (AGR + 14) = –2.0135 + 0.0895 Ln Bw + 0.5087 T – 0.0142 T² + 0.2997 D (R² = 71.79; ANOVA p < 0.0001) and Ln (AFR) = – 5.6577 + 0.5137 Ln Bw + 0.5266 T – 0.0132 T² + 1.1135 D (R² = 78.71; ANOVA p < 0.0001), where AGR: absolute growth rate, AFR: absolute feeding rate, Bw: body weight, T: temperature and D: diet. In our experimental conditions, sex did not affect growth or food intake. The optimum temperature for growth (17.5 °C) and food intake (20 °C) was independent of body weight. Growth and food intake were higher with the crab diet. Nevertheless, food efficiency was better for animals fed on fish (bogue). Maximum food efficiency was reached at 16.5 °C for both diets. When the temperature was above 23 °C, weight losses and mortality were recorded; the temperature at which this occurred depending on body weight and diet, so that smaller and bogue-fed individuals were more sensitive to increasing temperatures. O. vulgaris growth may provide optimum economic performance from 16 to 21 °C. This range is too narrow, considering the wide natural range (12–29 °C) in some Mediterranean areas. Therefore, O. vulgaris growth will be limited by seasonality of temperature or must be carried out with other systems (e.g. recirculation in closed systems with temperature control) for it to be economically viable.     

Effect of environmental calcium levels on calcium uptake in tilapia larvae Oreochromis mossambicus

Effects of environmental calcium concentrations on the survival, growth, body calcium content and calcium uptake kinetics in developing tilapia (Oreochromis mossambicus) larvae were studied. Fertilized eggs were incubated in high- and low-calcium artificial freshwater (0.88–0.96 mmol l^–1 vs. 0.02–0.03 mmol l^–1 CaCl₂ or CaSO₄) until 3 days after hatching. Tilapia larvae showed similar hatching rates and wet weights in either high- or low-calcium medium, indicating neither the development nor the growth in tilapia larvae was affected by the environmental calcium levels. The body calcium content in low-calcium groups was about 90–95% that of high-calcium groups, No matter what calcium source was used (CaCl₂ or CaSO₄), acclimation to low calcium medium caused a stimulation of calcium uptake (measured in 0.2 mmol l^–1 calcium),i.e., 1.2–1.3 fold higher than that of high calcium groups. This enhanced calcium uptake capacity was characterized by a 50% decrease in K_m and a 25% increase in J_max. Effect of different calcium salts on calcium influx was significant only in low calcium level,i.e., calcium influx in low-CaCl₂ group higher than that in low-CaSO₄ group. These results suggest that tilapia larvae are able to modulate their calcium uptake mechanism to maintain normal body calcium content and growth in environments with different levels of calcium.