Age and growth of the lizardfish <Emphasis Type="Italic">Saurida elongata</Emphasis> from the Tsushima/Korea Strait

We studied the age and growth of the lizardfish Saurida elongata using ground thin sections of otoliths (sagittae) from specimens collected in the Tsushima/Korea Strait between May 1999 and June 2001. A total of 695 individuals with fork lengths (FL) ranging from 189 to 478 mm were examined. The frequency of translucent zone occurrence at the outer margin of the otoliths indicated that translucent zones formed once a year between November and February. Most of the males examined were estimated to be 2–7 years old and the females, 3–9 years old. The maximum estimated age of a male specimen was 10 years and that of a female, 11 years. The estimated von Bertalanffy growth curves were FL _t  = 451{1 − exp[−0.172(t + 2.50)]} and FL _t  = 515{1 − exp[−0.151(t + 2.47)]} for males and females, respectively. At all ages, the FL at a specific age for females was greater than that for males, suggesting that females of this species grow faster than males.     

Age and growth of two gizzard shads, <Emphasis Type="Italic">Nematalosa come</Emphasis> and <Emphasis Type="Italic">N. japonica</Emphasis>, in coastal waters around Okinawa Island,southwestern Japan

The age and growth of two Nematalosa species around Okinawa Island were examined using sectioned otoliths collected from September 2003 to April 2006. Monthly changes in the frequency of the appearance of a translucent band on the outer margin of the otoliths indicated that ring formation occurred once a year from January to July for Nematalosa come and from January to March for Nematalosa japonica. The von Bertalanffy growth equations for both species were as follows: N. come: L _t  = 365.5{1 − exp[−0.111 × (t + 0.288)]} for females and L _t  = 214.7{1 − exp[−0.700 × (t – 1.110)]} for males; N. japonica: L _t  = 205.1{1 − exp[−1.068 × (t − 1.180)]} for females and L _t  = 195.5 {1 − exp[−1.293 × (t − 1.269)]} for males. The maximum ages observed for N. come and N. japonica were 11 and 6 years old, respectively. The growth of these species was characterized by the slow growth of N. come over many years, resulting in a larger size than N. japonica.     

Growth,diet, and reproduction of Eurasian perch <Emphasis Type="Italic">Perca fluviatilis</Emphasis> L. in Lake Varese,northwestern Italy

No data have previously been reported on Eurasian perch Perca fluviatilis L. in Lake Varese. In this study, the growth, diet, and reproductive biology of the Eurasian perch population were investigated with the aim of providing information that may serve as a basis for efficient resource management. A total of 240 specimens were caught during the monthly sampling campaign from November 2006 through October 2008. The length-to-weight relationships were W _t = 8.4 × 10⁻³ L _t^3.10 (males) and W _t = 4.1 × 10⁻³ L _t^3.36 (females). The parameters for the von Bertalanffy growth function for pooled sexes were L _∞  = 33.17 cm, k = 0.20 year⁻¹, and t ₀ = −1.34 year. Perch in Lake Varese spawn from April through May. Sexual maturity is reached when males are 2 years old, in females mostly when they are 3 years old. Relative fecundity (F _rel) and absolute fecundity (F _abs) were assessed for females. Fecundity values were similar to data reported for other European populations: females of age 2+ F _rel = 102,457 ± 12,275, age 3+ F _rel = 131,767 ± 5,891, and age 4+ F _rel = 131,252 ± 15,555. Perch diet spectrum was wide and somewhat characterized by season. Perch in Lake Varese feed on macroinvertebrates, mainly Chironomidae and Chaoborus, zooplankton, and juvenile rudd Scardinius erythrophthalmus.     

Osmoregulation in juvenile Chinese sturgeon (<Emphasis Type="Italic">Acipenser sinensis</Emphasis> Gray) during brackish water adaptation

The osmoregulation capabilities of 7-month-old juvenile Chinese sturgeon (Acipenser sinensis Gray) (128.8 ± 15 g) transferred directly from fresh water (0‰, 46 mOsmol kg⁻¹) to brackish water (10‰, 273 mOsmol kg⁻¹) were studied over a 20-day period. Changes in serum osmolarity, chloride (Cl⁻), sodium (Na⁺), potassium (K⁺) and calcium (Ca²⁺) ion concentrations, as well as gill and spiral valve Na⁺,K⁺-ATPase activities were measured at 3, 12, 24, 72, 216 and 480 h after transfer to BW. The serum osmolarity and ion concentrations (Na⁺, Cl⁻ and Ca²⁺) increased immediately after the transference to BW, reaching maximum at 24 h and returned to a new steady state at 216 h, while the FW control group maintained basal levels which showed lower (P < 0.05) than the BW group. Gill Na⁺,K⁺-ATPase activity of BW group exhibited an abrupt decrease in the first 3 h after transfer, but began to increase at 3 h, reaching a peak value at 24 h, and returned to a new steady state at 216 h. The differences between gill Na⁺,K⁺-ATPase activity of BW and FW fish were significant (P < 0.05) after 12 h. In contrast, Na⁺,K⁺-ATPase activity of the spiral valve showed transient increase after transference from FW to BW, and then decreased rapidly at 3 h, reaching the lowest at 24 h after transference. At 216 h after exposure to BW, Na⁺,K⁺-ATPase activities of the spiral valve increased slowly to the levels of FW control. The results of our study indicate the existence of hyposmoregulatory adaptive mechanisms in 7-month-old juvenile Chinese sturgeon which enable this fish to acclimate itself successfully to brackish water.     

Age, growth and life history of gunnel, Pholis fangi, in the Yellow Sea

We examined the formation of annuli by marginal observations on otoliths of gunnel (Pholis fangi) in the Yellow Sea to validate the age determination method and to derive the growth equation covering from larval to adult stages. Gunnels, ranging from 46 to 173 mm in total length, were collected by a bag net fishery from the western coastal waters off Korea from November 1998 to October 1999. Marginal observations indicated that the translucent zone (annual mark) on adult otolith was formed during the winter, whereas the opaque zone was formed during the summer. However, a translucent zone was formed between May and June in juvenile otoliths. This false ring was formed when the fish transited from the inshore pelagic life of larvae to the offshore bottom life of juveniles. The observed maximum age was 58 months. Using observed length-at-monthly age, growth in length was expressed by von Bertalanffy growth curve; L_t = 144.0 (1 − e^{−0.11 (t+0.43)}). P. fangi spawned in winter recruit to inshore, and grow quickly in the nursery habitats in spring. Gunnel inhabit the bottom offshore area during the summer season, and reappear inshore thereafter.     

The purification and development of a quantitative enzyme linked immunosorbent assay (ELISA) for the measurement of vitellogenin in diploid and triploid brook trout (Salvelinus fontinalis)

Vitellogenin (VTG) was purified from the plasma of estradiol-17β (E₂) treated male brook trout (Salvelinus fontinalis; bt) using gel filtration and anion exchange chromatography. An antiserum to bt-VTG was raised in rabbits, then used to detect bt-VTG by Western blot analysis. Purified bt-VTG and its antibody were then used to develop an antibody-capture, competitive enzyme-linked immunosorbant assay (ELISA). Confirmation of the purified protein as bt-VTG was based on the characteristics of high molecular weight (∼562 kDa), dominant plasma protein in vitellogenic females and induction by exogenous E₂ treatment in males. The antiserum recognized a major 184 kDa polypeptide as well as minor bt-VTG degradation products (150–66 kDa) in purified bt-VTG and in plasma from vitellogenic females. Low levels of antibody cross reactivity were shown with plasma from nonvitellogenic females, control rabbit serum, and several other antisera known to not contain VTG. The ELISA had a minimum detection limit of 8 ng ml⁻¹ and intra- and inter-coefficients of variation less than 9% and 15%, respectively. The ELISA demonstrated parallel binding slopes among dilution curves of purified bt-VTG standard and plasma from diploid and triploid brook trout females. Using the ELISA, maximum plasma VTG levels of 93.5±33.6 mg ml⁻¹ were detected in vitellogenic diploid females, whereas only 0.18±0.15 mg ml⁻¹ were detected in triploid females of the same age (n=5 for each). Diploid and triploid males cohabitating with vitellogenic females showed measurable levels of plasma VTG during vitellogenesis in females (i.e., 0.17 and 0.06 mg ml⁻¹, respectively (n=1)). This revised version was published online in August 2006 with corrections to the Cover Date.     

Substrate specificity of brain acetylcholinesterase and its sensitivity to carbamate insecticides in <Emphasis Type="Italic">Carassius auratus</Emphasis>

The substrate specificity of brain acetylcholinesterase (AChE) in adult Carassius auratus fish and its sensitivity to carbamate insecticides were investigated in vitro. The results showed that the order of four substrates hydrolyzed by brain AChE in C. auratus was acetylthiocholine iodide > β-methylthiocholine iodide > propionylthiocholine iodide > butyrylthiocholine iodide, and the maximum velocity (V _max) of AChE hydrolyzing acetylthiocholine iodide (ATCh) was the highest among the four substrates, and the V _max values were 0.067 and 0.082 mmol min⁻¹ mg⁻¹ for male and female fish respectively. But their Michaelis–Menten constants (K _m) were the lowest, only 0.071 and 0.072 mmol/l respectively. Compared with other carbamate insecticides, the sensitivity of brain AChE to carbofuran was the highest and the IC₅₀ values were 1.04 × 10⁻⁶ mol/l for females and 1.17 × 10⁻⁶ mol/l for males. The inhibitory tendencies of eserine, methomyl, and aldicarb to brain AChE were very similar, and the percentage inhibition increased with time at the concentration of 1 × 10⁻⁶ mol/l. The order of inhibition potential of the three inhibitors from the highest to the lowest was eserine, aldicarb, and methomyl.     

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.     

Effect of stocking density on survival and growth performance of pikeperch, <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.), larvae under controlled conditions

The effect of stocking density on the survival and growth of pikeperch, Sander lucioperca (L.), larvae was examined in two consecutive experiments. In experiment I, 4-day-old larvae [body wet weight (BW): 0.5 mg; total body length (TL): 5.6 mm] were reared in 200-l cylindro-conical tanks in a closed, recirculating system (20 ± 0.5°C) at three stocking densities (25, 50 and 100 larvae l⁻¹) and fed a mixed feed (Artemia nauplii and Lansy A2 artificial feed) for 14 consecutive days. At densities of 25 and 100 larvae l⁻¹, growth rate and survival ranged from 2.7 to 1.9 mg day⁻¹ and from 79.2 to 72.3%, and fish biomass gain ranged from 0.6 to 2.0 g l⁻¹, respectively. There were two periods of increased larval mortality: the first was at beginning of exogenous feeding and the second during swim bladder inflation. In experiment II, 18-day-old larvae (BW: 35 mg; TL: 15.6 mm) obtained from experiment I were reared under culture conditions similar to those of experiment I, but at lower stocking densities (6, 10 and 15 larvae l⁻¹). The fish were fed exclusively with artificial feed (trout starter) for 21 consecutive days. At densities of 6 and 15 larvae l⁻¹, the growth rate and fish biomass gain ranged from 28.8 to 23.1 mg day⁻¹ and from 2.0 to 3.3 g l⁻¹, respectively. The highest survival (56.5%) was achieved at a density of 6 larvae l⁻¹. Mortality at all densities was mainly caused by cannibalism II type behaviour (27–35% of total). In both experiments, growth and survival were negatively correlated and fish biomass gain positively correlated with stocking densities. The present study suggests that the initial stocking density of pikeperch larvae reared in a recirculating system can be 100 individuals l⁻¹ for the 4- to 18-day period post-hatch and 15 individuals l⁻¹ for the post-19-day period.     

不同月龄缢蛏新品种数量性状的相关与通径分析

为了检测缢蛏新品种"申浙1号"不同月龄数量性状间的相关性。随机选取4、9、11月龄缢蛏个体60个以上,测量其壳长(SL)、壳高(SH)、壳宽(SW)、活体质量(W),采用相关与通径分析方法分析壳形态性状对活体质量的作用效果。结果显示,各数量性状之间的相关关系均达到极显著水平,其中与4、11月龄质量相关系数最大的是壳长,分别为0.911、0.631,与9月龄活体质量相关系数最大的是壳高,为0.653。通径分析结果显示,对4、9、11月龄活体质量的直接影响最大的分别是壳长(0.562)、壳宽(0.433)、壳高(0.394),决定系数与以上通径分析结果的变化趋势一致。利用逐步回归的方法分别建立4、9、11月龄缢蛏活体质量(W)的最优回归方程:W4=–0.756+0.039SL+0.112SW,R2=0.849;W9=–10.622+0.095SL+0.404SH+0.644SW,R2=0.631;W11=–23.772+0.207SL+0.805SH+0.587SW,R2=0.909。研究结果为缢蛏人工选育过程中的亲贝选择和产量预测等提供了基础数据。     

Endocrine and gonadal changes during the annual reproductive cycle of the freshwater teleost,Stizostedion vitreum

The annual reproductive cycle of walleye (Stizostedion vitreum) was characterized by documenting changes in gonadal development and serum levels of estradiol-17β (E₂), testosterone (T), 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P), and 11-ketotestosterone (11-KT) in wild fish captured from upper midwestern lakes and rivers throughout the year. Fish from the populations used in this study spawn annually in early- to mid-April. Walleye showed group synchronous ovarian development with exogenous vitellogenesis beginning in autumn. Oocyte diameters increased rapidly from ∼ 200 μm in October to ∼ 1,000 μm in November, and reached a maximum of 1,500 μm just prior to spawning. Changes in gonadosomatic indices (GSIs) paralleled changes in oocyte diameters. Serum E₂ levels in females increased rapidly from low values in October (< 0.1 ng ml⁻¹) to peak levels of 3.7 ng ml⁻¹ in November, coinciding with the period of the most rapid ovarian growth. Subsequently, E₂ levels decreased from December through spawning. Serum T levels exhibited a bimodal pattern, increasing to 1.6 ng ml⁻¹ in November, and peaking again at 3.3 ng ml⁻¹ just prior to spawning. We detected 11-KT in the serum of some females at concentrations up to 5.6 ng ml⁻¹, but no seasonal pattern was apparent. In this study (unlike our results in a related study) 17,20-P was not detected. In males, differentiation of spermatogonia began in late August, and by January the testes were filled (> 95% of germ cells) with spermatozoa. Mature spermatozoa could be expressed from males from January through April. GSIs ranged from 0.2% (post-spawn) to 3.2% (pre-spawn). Serum T levels rose from undetectable levels in post-spawn males to 1.6 ng ml⁻¹ by November, remained elevated throughout the winter, and peaked at 2.8 ng ml⁻¹ I prior to spawning. Levels of 11-KT in males remained low (< 10 ng ml⁻¹, from post-spawning through January, then increased significantly by March and peaked just prior to spawning at 39.7 ng ml⁻¹. Our results indicate that vitellogenesis and spermatogenesis are complete or nearly so, in walleye by early winter, and suggest that it may be possible to induce spawning in this species several months prior to the normal spawning season by subjecting fish to relatively simple environmental and hormonal treatments.     

Effect of the interaction between body weight and temperature on growth and maximum daily food intake in sharpsnout sea bream (<Emphasis Type="Italic">Diplodus puntazzo</Emphasis>)

In experimental culture conditions in tanks, the effect of weight (W: 11–452 g) and temperature (T: 14–29°C) on the growth rate (SGR, % bw day⁻¹) and maximum daily food intake (SFR, % bw day⁻¹) in sharpsnout sea bream (Diplodus puntazzo) was studied. The possible combined effect of both independent variables (W and T) was also analyzed by multiple regression analysis, fitting the data to the equation Ln Y = Ln a + b Ln W + cT + dT ² + eT Ln W. Both SGR and SFR, and therefore feed efficiency (FE = SGR/SFR), were significantly influenced by the interaction between temperature and weight and may be expressed by means of the following equations: Ln SGR = −6.1705 + 0.5809T − 0.0087T ² − 0.0249T Ln W ( R_\textadj² R_{\text{adj}}^{2}  = 0.949; ANOVA P < 0.0001); Ln SFR = −4.8257 + 0.4425T − 0.0063T ² − 0.0163T Ln W ( R_\textadj² R_{\text{adj}}^{2}  = 0.964; ANOVA P < 0.0001).The results suggest that the optimum temperature for SGR and FE (T _SGRopt and T _FEopt), and the temperature at which the maximum SFR (T _SFRmax) is reached, decreases with body weight, in accordance with the equations: T _SGRopt = 33.297 − 1.435 Ln W; T _FEopt = 29.332 − 1.890 Ln W; and T _SFRmax = 34.941 − 1.304 Ln W, respectively. In this way, T _SGRopt is 28.4, 26.7, and 24.7°C; T _SFRmax is 30.5, 28.9, and 27.1°C and T _FEopt is 22.9, 20.6, and 18°C for 30, 100 and 400 g body weight, respectively.     

Longline hook selectivity for red tilefish Branchiostegus japonicus in the East China Sea

The catch of red tilefish by the Japanese longline fishery in the East China Sea has steeply declined during the last two decades, and resource management is clearly required. This study presents the size selectivity of hooks for red tilefish as a method to control first capture size, based on the results of longline fishing experiments using “Tainawa-bari” hooks of several sizes: Japanese nominal sizes J#10, J#11, J#12, J#13, J#14 and J#16. On the assumption of geometrical similarity in the combination of upper jaw length u and hook width g at a given retention probability, a single master curve s(R) = exp (−14.42 + 8.85R)/(1 + exp [−14.42 + 8.85R]) was estimated in terms of relative upper jaw length to hook width, R = u/g, using the SELECT method based on a multinomial distribution. The relative upper jaw length for 50% retention is 1.63, and the selection range is 0.25. Almost all fish over 300 mm in total length were retained by a hook of size J#12, but smaller fish with less commercial value were also caught. Moreover, J#10 hooks catch fish with total lengths of >250 mm efficiently. This indicates that J#10 and J#12 hooks that are currently used are too small to optimize yield per recruit and also for resource conservation.     

Age and growth of threeline grunt <Emphasis Type="Italic">Parapristipoma trilineatum</Emphasis> along the south-western coast of Kii Peninsula,Japan

Age and growth were determined for threeline grunt Parapristipoma trilineatum based on otolith readings of 1043 specimens collected along the south-western coast of Kii Peninsula, Japan. Observations of the otolith margin, together with comparisons of ring mark counts with age in artificially reared specimens, verified that such marks were produced once a year. The formation period corresponded approximately to the main spawning season (May–June). Both surface and cross-section methods were used for age determination; the surface method often resulted in underestimations of age for fish older than 2 years. Discrepancies between the two methods became greater with fish growth. The von Bertalanffy growth curve, based on ages inferred from the cross-section method, was FL _t=331×{1−exp[−0.283×(t+1.45)]}. No substantial difference was detected between male and female growth parameters. The oldest maximum ages inferred from the cross-section method were 15 and 21 years for females and males, respectively. It seems likely that P. trilineatum grows more slowly and lives longer than previously thought, and the difference is attributed primarily to differences in aging methods used in the present and previous studies.     

Parentage assignment of stocked black sea bream <Emphasis Type="Italic">Acanthopagrus schlegelii</Emphasis> in Hiroshima Bay using microsatellite DNA markers

The genetic contribution of 51 broodstock, comprising 29 females and 22 males, reared at Hiroshima City Marine Products Promotion Center for the production of stocked black sea bream was monitored during two consecutive years using seven microsatellite DNA loci. The high discrimination ability of these markers was reflected in the polymorphic identification content (PIC=0.831), the exclusion probability (Q≈1), and the low probability of identity index (I=3.635⁻¹⁰). The total number of breeders contributing to the mating process was estimated at 32 (62.7%) in 2000 and 30 (58.8%) in 2001. On pedigree reconstruction, 69.3% of the offspring were successfully assigned to a single broodstock pair. Loss of alleles accounted for 16.9% during seed production; nevertheless, 90.9% of males and 69.0% of females participated in the mating process. Based on microsatellite genetic tagging, 58.9% of the fish sampled during the two months after release were identified as hatchery stock, presenting no significant differences from wild conspecifics in either fork length or body weight.     

Acute toxicity of nitrite on tilapia (Oreochromis niloticus) at different external chloride concentrations

Tilapias (Oreochromis niloticus) juveniles (total length 4.9 ± 0.2 cm and weight 1.8 ± 0.2 g) were exposed to several nitrite concentrations (0, 10, 18, 32, 56 and 100 mg l⁻¹) for 96 h, using a semi-static renewal method at chloride levels of 35.0 and 70.0 mg l⁻¹. At the end of the 96-h period, the median lethal concentration (LC₅₀) of nitrite was 28.18 mg l⁻¹ in water with low chloride content (35.0 mg l⁻¹) and 44.67 mg l⁻¹ with high chloride content (70.0 mg l⁻¹, respectively). It indicated that high concentrations of chloride ions could reduce the toxicity of nitrite. During the toxicity experiments, the behaviour and clinical signs of tilapias were also observed. Furthermore, the test of toxic mechanism was designed taking five test concentrations, viz., 5, 10, 15 and 20 mg l⁻¹ and a nitrite-free control. Nitrite exposure produced high levels of methaemoglobin (MHb) but did not seem to cause mortality, as surviving tilapias showed high levels (85.37 ± 2.23 and 53.82 ± 3.44 at 35.0 and 70.0 mg l⁻¹ chloride, respectively). The percentage of MHb exposed to nitrite was significantly higher (P<0.05) than the control (0 mg l⁻¹ nitrite) and increased with the increasing nitrite concentration. However, the percentage of MHb decreased with the increasing chloride concentration.     

Age and growth estimates of the sharptail mola,Masturus lanceolatus,in waters of eastern Taiwan

The sharptail mola, Masturus lanceolatus, is one of the largest teleost fishes in the world, and can be found in warm temperate and tropical regions worldwide. The increase of sharptail mola catch in the eastern Taiwan in recent years stimulated a concern that increasing exploitation of this species might lead to a decline of the stock. However, biological information of this species is very limited. Hence, this study provides the first information on age and growth of this species in the waters off eastern Taiwan based on 265 specimens (105 females and 160 males) collected from January 2003 to November 2006 at the Nanfanao and Hualien fish markets, eastern Taiwan. The relationships between whole weight (W) and standard length were expressed as: W = 9.98 × 10^?4 SL^2.45 (n = 105, p < 0.01) for females, and W = 3.33 × 10^?4 SL^2.68 (n = 160, p < 0.01) for males. Based on the MIR analysis, growth band pairs (including translucent and opaque bands) in vertebrae formed once a year and were counted up to 23 and 16 for females and males, respectively. Three growth functions, the von Bertalanffy (VBGF), Robertson, and Gompertz, were used to model the observed length at age data. The VBGF had the best fit and predicted an asymptotic length (L_∞) = 262.5 cm SL, growth coefficient (k) = 0.046 yr^?1, age at zero length (t₀) = ?3.350 yr (n = 80, p < 0.01) for females, and L_∞ = 231.0 cm SL, k = 0.059 yr^?1, t₀ = ?1.852 yr (n = 135, p < 0.01) for males. The longevities were estimated to be 105 and 82 yr based on the VBGF for females and males, respectively.     

星康吉鳗形态性状与体重的通径分析及生长曲线拟合

为探明星康吉鳗（Conger myriaster）形态性状和体重的关系，测定了体重（Y）及全长（X₁）、肛长（X₂）、尾长（X₃）、头长（X₄）、吻长（X₅）、眼径（X₆）、眼后头长（X₇）、背鳍前长（X₈）、躯干长（X₉）、头宽（X₁₀）、眼间距（X₁₁）等11个形态性状，通过相关分析、通径分析、回归分析等方法研究了形态性状对体重的影响；通过曲线拟合获得4个形态性状与体重的最佳拟合模型。结果表明，星康吉鳗各形态性状之间以及形态性状与体重之间均呈极显著正相关关系（P< 0.01）。相关分析发现肛长（X₂）与体重的相关系数最大（0.970）；通径分析发现肛长（X₂）对体重的直接作用最大（0.450），头宽（X₁₀）通过肛长（X₂）对体重的间接作用最大（0.431）；决定系数分析发现，肛长（X₂）对体重的直接决定系数最大（0.203），肛长（X₂）和头宽（X₁₀）的共同决定系数最大（0.172）。形态性状（X）与体重（Y）的多元回归方程为Y=-113.859+6.481X₂+49.213X₆+11.514X₇+20.145X₁₀（R²=0.954）。星康吉鳗肛长（X₂）、眼后头长（X₇）、头宽（X₁₀）与体重的最佳拟合模型为指数函数，模型方程分别为Y=1.466e^0.287X、Y=1.435e^1.328X、Y=1.970e^1.974X，眼径（X₆）与体重的最佳拟合模型为线性，方程为Y=-77.460+222.093X。结论认为，在星康吉鳗选育时，应以肛长（X₂）和头宽（X₁₀）为主要选择性状，以眼径（X₆）和眼后头长（X₇）为辅助选择性状。     

Thyroid hormone concentrations in the gonads of wild chum salmon during maturation

Changes in gonadal and plasma concentrations of thyroid hormones were examined at various stages of maturation in chum salmon (Oncorhynchus keta) caught in the Bering Sea and the Bay of Alaska. Plasma concentrations of thyroxine (T₄) were less than 5 ng ml⁻¹, and those of 3,5,3′-triiodo-L-thyroxine (T₃) were less than 2 ng ml⁻¹ I in both males and females, regardless of the degree of sexual maturity or the gonadosomatic index (GSI). There was no clear relationships between circulating thyroid hormone levels and tissue levels. The ovarian T₄ concentrations were undetectable (less than 0.2 ng g⁻¹) or less than 2 ng g⁻¹ when GSI was lower than 1%, but increased thereafter and reached a plateau of 8–10 ng g⁻¹ when GSI became 2%. The ovarian T₃ concentrations were about 5 ng g⁻¹ when GSI was 1%, increased to a maximum level (20 ng g⁻¹) when GSI was about 2%, and decreased to a constant level of 10 ng g⁻¹ thereafter. The T₄ and T₃ content in single oocyte increased proportionally to the oocyte volume, indicating a constant incorporation of the hormones into the oocyte. The T₄ concentrations in the testis were 1 ng g⁻¹ or less regardless of the GS1. On the other hand, the T₃ concentrations were highest (15 ng g⁻¹) when the GSI was less than 1%, decreased thereafter when spermatocytes appeared in the testis, and became about 5 ng g⁻¹ I in testes containing spermatozoa, raising the possibility of a role for T₃ during early gamete and/or gonad maturation of testes.     

How to determine the appropriate mortality in experimental larval rearing?

Survival in larval rearing experiments is difficult to estimate due to accidental losses and periodic sampling. The number of sampled fish can be a large proportion of the stocked ones, making it difficult to calculate the overall survival rate and mortality coefficient as this is based on the initial number. Here, a new method of calculating survival is proposed using the mortality coefficient. When the initial stocking density and sampled and final numbers are known, and assuming that mortality coefficient is constant, the final number of fishes can be represented by the formula N _t = e^−mt (N ₀ − ΣN _Sne ^mdn), where t is rearing period (days), N ₀ indicates initial number, N _t indicates the survival number at t days of rearing, m is the natural mortality coefficient, N _Sn is the sampled number in the nth sampling, and dn is the rearing period until removal of the nth sample. The provisional mortality coefficient is calculated from initial and final stocking numbers. Then values for the natural mortality coefficient are substituted into the formula with successive approximation. The coefficient, which most closely approximates the actual survival, is determined as the best fit natural mortality coefficient. Examples of larval experiments are provided to demonstrate the method and show that survival is often underestimated using traditional methods.