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.     

Age validation,growth and annual reproductive cycle of chub mackerel <Emphasis Type="Italic">Scomber japonicus</Emphasis> off the waters of northern Kyushu and in the East China Sea

The age and growth of chub mackerel Scomber japonicus collected from the East China Sea and the northern waters off Kyushu between June 2000 and June 2001 were determined by observing the otolith surface after dipping it in xylene. The translucent and opaque zones on the otolith surface were identified, and the number of translucent zones was counted. Monthly changes in the frequency of fish with translucent zones on the otolith margin, and in the marginal increments, indicated that the translucent zones were formed between April and June. The seasonal pattern of annulus formation on the otolith became clear by observing the otoliths of fish with known ages, and the otolith formation in wild fish was consistent with that of fish with known ages. The mean gonadosomatic index of male and female fish was high from March to May, and spawning females were observed from mid-March to mid-May. The estimated ages were 1–5 years for males and 1–6 years for females. The von Bertalanffy growth parameters did not significantly differ between male and female. The model was obtained as FL _t=406×{1−exp[−0.372×(t+1.68)]     

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.     

Age and growth of Gerres sp. (Perciformes: Gerreidae) in Okinawa Island of Southern Japan

A total of 518 Gerres sp. were collected around Okinawa Island, Japan, from November 2002 to July 2005, with monthly sampling where the standard length of females (n=218) were 56.2–147.1 mm, and males (n=149) were 62.2–139.4 mm. The maximum ages observed for females were 5⁺ years and males were 4⁺ years, estimated by transverse sectioned sagittal otoliths. Mean marginal increment indicated that opaque rings were formed once a year during April to July. The standard length (SL; mm) — body wet weight (BW; g) relationships were described as BW=(3.26×10⁻⁵) SL^2.97 and BW=(3.13×10⁻⁵) SL ^2.98 for females and males, respectively, and the standard length at age described by von Bertalanffy growth function for females, L _t=137.1(1−e^{−0.80[t+0.80]}) and males, L _t=127.3(1−e^{−0.82[t+0.93]}).     

Age,growth, maturity,and sex changes of monogrammed monocle bream Scolopsis monogramma in the waters around Okinawa-jima Island,Japan

Age, growth, maturity, and sex changes of the monogrammed monocle bream Scolopsis monogramma were estimated from ca. 500 specimens collected at Okinawa-jima Island in southern Japan. Age was determined from sectioned otoliths: maximum ages were 10 years for females and 9 years for males. Parameters for von Bertalanffy growth functions were L _t  = 206.6{1 ? exp[?0.68(t + 0.81)]} (n = 337) for females and L _t  = 244.4{1 ? exp[?0.93(t + 0.32)]} (n = 130) for males. The spawning season was estimated to last from June to July, with a peak in July. The standard length (SL) and age at 50 % maturity for females were estimated as 186.4 mm SL and 3.3 years, respectively. Intersex individuals appeared from 159.6 to 237.5 mm SL (n = 16) in fish between 1 and six years old, with the highest frequencies occurring at 170 mm SL and 2 years old. Hence, almost all S. monogramma specimens found at Okinawa-jima Island exhibited pre-maturational sex change, although some may have been protogynous hermaphrodites. Biological characteristics such as age at growth, maturation, and spawning season are valuable factors that can inform the resource management of local fisheries.     

Growth,sex ratio,and maturation rate with age in the blackspot tuskfish <Emphasis Type="Italic">Choerodon schoenleinii</Emphasis> in waters off Okinawa Island,southwestern Japan

The growth, sex ratio with age, and age at sexual maturation were determined based on sectioned otoliths in 257 specimens of the blackspot tuskfish Choerodon schoenleinii collected in waters off Ryukyu Island. Opaque rings observed by reflected light in the sectioned otoliths were found to form once a year from January to July. The three growth parameters of the von Bertalanffy growth equation were L_∞ = 68.1 (cm), k = 0.263, and t ₀ = −0.023 (year). The age at which the sex ratio reached 50% by sexual transition was about 6.15 years, and the age at which 50% of females were sexually mature was approximately 2 years. The oldest specimen among the samples was 17 years old.     

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.     

Comparison between surface-reading and cross-section methods using sagittal otolith for age determination of the marbled sole <Emphasis Type="Italic">Pseudopleuronectes yokohamae</Emphasis>

To find an appropriate method for age determination in the marbled sole Pseudopleuronectes yokohamae in Tokyo Bay, Japan, sagittal otoliths of 1,343 individuals were observed by surface-reading and cross-section methods and the results were compared. Opaque zones occurred once a year and were regarded as annuli in both methods. The surface-reading method sometimes provided a lower count of the number of annuli than the cross-section method, and the frequency of this discrepancy was highest in older fish (males above 5 years, females above 4 years). The oldest female fish was estimated to be age 10 years by the cross-section method but 8 years by the surface-reading method. The cross-section method could provide a more accurate estimate of age and is therefore likely to be indispensable to estimations of longevity. In contrast, the surface-reading method is superior in terms of cost and time efficiency but is likely to underestimate the ages of older fish. However, growth equations based on age estimated by the surface-reading method were sufficiently accurate if males ≥5 years and females ≥4 years were combined as specific, single age groups of 5+ and 4+, respectively.     

Age,growth and maturation of the redbelly tilapia <Emphasis Type="Italic">Tilapia zillii</Emphasis> introduced into the Haebaru Reservoir on Okinawa-jima Island

ABSTRACT:   The age, growth and maturation of the redbelly tilapia Tilapia zillii introduced into the Haebaru Reservoir on Okinawa-jima Island were studied using 2197 specimens ranging from 7.3 to 168.0 mm standard length (SL). The spawning season was estimated to be from April to August, with a peak in April and May. The first maturation sizes of females and males were estimated to be 38.1 and 33.0 mm SL, respectively. The opaque zones in otoliths that form annually were found to correlate with the spawning season. Maximum ages of females and males were 7 and 6 years, respectively. The von Bertalanffy growth formulae were expressed as: L _t  = 99{1 − exp[−0.67( t  + 0.09)]} for females and L _t  = 155{1 − exp [−0.36( t  + 0.12)]} for males. Males grew to be larger than females from the first year onward. Populations of this species are characterized by early maturation life history parameters and are thought to adapt and become established quickly after being released into new water systems. Furthermore, extermination activity in winter is thought to be an effective strategy before the newly recruited fish begin breeding in the warmer months.     

Age and maturation of jack mackerel Trachurus japonicus in the East China Sea

Growth and reproductive characteristics of jack mackerel Trachurus japonicus collected in the East China Sea were determined based on otolith readings and gonad histology, respectively. Translucent and opaque zones on sectioned otoliths were identified and opaque rings counted. Von Bertalanffy growth parameters did not significantly differ between males and females, and the combined growth curve was: L _t  = 401{1 ? exp[?0.275 (t + 1.149)]} (0.8 < t < 6.9), where L _t is fork length (mm) at age t. The calculated lengths at age 1 in our study were larger than those reported 50 years ago from the East China Sea. The spawning period was evaluated to be from December to June, but primarily from February to May, based on the monthly changes in the gonadosomatic index and histological observations. The minimum size and age at first maturity were smaller and younger, respectively, than those reported in previous studies.     

Ex situ and in situ measurements of juvenile yellowfin tuna <Emphasis Type="Italic">Thunnus albacares</Emphasis> target strength

To provide target strength (TS) information for estimating the body length of yellowfin tuna Thunnus albacares and its abundance around fish aggregating devices, TS was measured ex situ and in situ. In the ex situ TS measurements, two cameras synchronized with a 200 kHz echosounder were used to obtain the precise orientation of the yellowfin tuna under free swimming conditions. The ex situ TS (dB re 1 m²)–fork length (FL, cm) regression was: TS = 27.06 log (FL) − 85.04. Ex situ TS was found to reach its maximum in the tilt angle range of −15° to −20° after excluding TS samples with insignificant correlation to the tilt angle. The angle between the vertebra and the swim bladder was approximately 25° according to X-ray images, supporting the above tilt range. The relationship between the swim bladder volume (V _SB, ml) and the fork length was: V _SB = 0.000213 FL³. The results from the in situ TS measurements indicated that the tilt angle was highly concentrated between −10° and 15°. The results from a calculation using the ex situ TS–FL equation with the fork length from biological sampling agreed strongly with the average in situ TS.     

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.     

Age determination and growth of Pacific bluefin tuna, Thunnus orientalis, off Japan and Taiwan

Age determination of wild captured Pacific bluefin tuna, Thunnus orientalis, was conducted using sagittal otoliths of 806 specimens (47–260 cm in fork length) caught in the waters off Japan and Taiwan. Otoliths were transversely sectioned and the opaque and translucent zones were analyzed. Opaque zones mainly appeared on the otolith edge from April to July, indicating that the opaque zone is formed annually. The opaque zones formed during later life (age 10+) were more distinct than the earlier zones. The estimated ages of specimens ranged from 1 to 26 years. Parameters of the von Bertalanffy growth function were estimated to be 249.6 cm, 0.173, and −0.254 years for L_∞, k, and t₀, respectively. Growth of younger fish was rapid up to 5 years old attaining about 150 cm, and then growth rate decreased. After that, fish attained about 200 cm at 9 years old and about 225 cm (90% of L_∞) at 13 years old (50% of maximum age). This paper updates the biological information on length at age with a large size range to support stock assessment model analyses for this commercially valuable species.     

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.     

Age and changes in growth of the king weakfish Macrodon atricauda (Günther, 1880) between 1977 and 2009 in southern Brazil

The coastal demersal sciaenid Macrodon atricauda (Günther, 1880), formerly M. ancylodon (Bloch and Schneider, 1801) was sampled for ageing during four periods (1977–1979, 1984–1986, 1997–1998 and 2006–2009) in commercial fishing and scientific surveys along southern Brazil (Lat. 30°S–34°40′S). Maximum observed age was seven years, but no fish over five years old was sampled in the last period. Marginal increment analysis of thin sections validated ageing and showed that opaque and translucent bands were laid down at all ages in spring–summer and autumn–winter, respectively. Ageing M. atricauda based on sectioned otoliths is highly recommended because comparisons with readings on whole otoliths showed that ages based on whole otoliths exceeded those based on sectioned otoliths for 56.5% of the aged specimens. The growth of M. atricauda has increased in the last four decades, most noticeably in the case of adult males over two years old and females over three years old. A threefold decrease in its density and the demersal fish community as a whole are the most likely causes of the growth increase.     

Age, growth, and reproductive characteristics of dolphinfish Coryphaena hippurus in the waters off west Kyushu, northern East China Sea

The growth and reproductive characteristics of dolphinfish Coryphaena hippurus collected in the waters off western Kyushu from May 2008 to April 2011 were determined based on scale and otolith readings and gonad histological examinations, respectively. Based on annual increments in scales and daily increments in sagittal otoliths, the von Bertalanffy growth curves in male and females were determined as $ FL_{t} = 1049[1 - \exp \{ - 0.835(t + 6.975 \times 10^{ - 14} )\} ] $ and $ FL_{t} = 938[1 - \exp \{ - 1.029(t + 6.975 \times 10^{ - 14} )\} ] $ , respectively, where FL _t is the mean fork length (mm) at age t. The spawning period was found to last from June to August for dolphinfish, based on an examination of the monthly changes in the gonadosomatic index and histological observations. Therefore, based on the relationship between the fork length and the developmental stage of the testes or ovaries, male and female dolphinfish were found to reach sexual maturity by the following spawning season after hatching in the northern East China Sea.     

Biological parameters of the bathyal fish black scabbardfish (Aphanopus carbo Lowe, 1839) off the Canary Islands, Central-east Atlantic

The main biological characteristics for black scabbardfish in the Canary Islands waters were established, focusing on its reproductive behaviour and strategy and its growth pattern. The sex proportion differs significantly from the 1:1 ratio, being clearly unbalanced towards the females. The sex ratio according to depth clearly shows the presence of male and female individuals in all the studied layers, thus sex segregation does not happen according to depth. The Canaries can be considered to be a reproduction site for A. carbo, since samples showing all stages of maturity have been observed. The gonadosomatic index (GSI) showed that the mean values were higher in the third and fourth quarters of the year. The index values clearly allow the differentiation of the individuals in resting or in spent (II and V) stages from individuals in ripe or in ripe and running stages, indicating that index levels higher than 2 are typical of maturation followed by spawning process. Up to twelve marks, assumed to be annuli, were visible in the sampled otoliths. Three to five years old were the dominant age classes and only 7.7% of fish were 7 years old or older. Age estimates ranged between 2 and 8 years for males and between 2 and 12 years for females. Estimated growth parameters were: L_∞ = 1477 ± 18.73 mm; k = 0.200 ± 0.016 year⁻¹; and t₀ = −4.58 ± 0.413 year. Biological aspects of the black scabbardfish suggest that this species has a generalist life-history strategy.     

Effect of temperature on the development of eggs and the daily pattern of spawning of round herring <Emphasis Type="Italic">Etrumeus teres</Emphasis>

Effect of temperature on the development of eggs of round herring Etrumeus teres was experimentally examined to construct a temperature-dependent egg development model. Mature fish were collected in the field and their eggs were artificially fertilized onboard. The eggs were incubated at nine temperatures set between 14.0 and 25.0°C. All eggs at the lowest three temperatures, 14.0°C, 15.0°C, and 16.0°C, ceased development and died at various stages before hatching. Durations required to hatching after fertilization ranged from 38.0 h at 25.0°C to 90.0 h at 17.5°C. The temperature-dependent egg development model, i.e., egg age in hours (y _i,t ) at the ith stage and temperature t (°C), was expressed as: y _i,t  = 4.604 × exp(−0.100 × t −0.129 × i) × i ^2.593. From the application of the model to early-stage eggs collected in the field, it is concluded that round herring starts spawning immediately after sunset and almost completes spawning by midnight. The temperature-dependent egg development model and the daily pattern of spawning presented in this study are essential tools for developing the daily egg production method to estimate the spawning stock biomass.     

Re-examination of age and growth of daggertooth pike conger Muraenesox cinereus in the western Seto Inland Sea, Japan

Age determination and growth using otolith rings in Muraenesox cinereus was re-examined in the western Seto Inland Sea, Japan. Previous study in this area indicated that new rings were formed annually from March to May, and then from September to October once individuals had achieved four or five rings. In this study, monthly changes in marginal growth rate indicated that the first ring was formed before November in the year following hatching, and from then on another ring was formed annually in July or August. The birth month was determined to be August based on a peak in monthly change in the gonad somatic index. Estimated von Bertalanffy growth functions were L = 806.6{1 ? exp[? 0.33(t + 0.06)]} and L = 1264.0{1 ? exp[? 0.19(t + 0.15)]} for males and females, respectively. Lengths after 3 years of age in this study were 100 mm longer than those in a previous study for both sexes.     

Application of synthetic hormone LHRH-A<Subscript>2</Subscript> on the artificial propagation of Persian sturgeon <Emphasis Type="Italic">Acipenser persicus</Emphasis>

For studying the effect of LHRH-A₂ hormone on the induction of final maturation and ovulation of Persian sturgeon, 71 matured females and 20 matured males were used. Five groups of breeders were injected with sturgeon pituitary gland hormone (50 mg per fish) and LHRH-A₂ in dosages of 3.5, 7, 8 and 10 μg kg⁻¹ for females and 3 and 5 μg kg⁻¹ for males. Results showed that LHRH-A₂ successfully induced final maturation and ovulation in females, and there was no significant difference between five groups of breeders in ovulation proportion, fertilization rate, survival rate of incubation, survival of yolk-sac absorption period and active feeding period of larvae. It can be concluded that the LHRH-A₂ is a proper alternative for pituitary gland hormone in artificial propagation of Persian sturgeon.