Population dynamics of Melicertus kerathurus (Decapoda: Penaeidae) in Thermaikos Gulf (N. Aegean Sea)

The east Atlantic-Mediterranean penaeid Melicertus kerathurus constitutes a valuable resource for Mediterranean fisheries. In recent years, its world production is almost totally based on the yields from Greece and Tunisia. A two-year study of prawn stock in Thermaikos Gulf (NW Aegean Sea) provided information on age, growth and mortality of the species. M. kerathurus exhibits a marked sexual growth dimorphism, with females showing an overall wider size range and greater size than males. Mean monthly size, CL_max were also in favor of females. Monthly age classes varied from one to four for females and from one to three for males, and corresponded to three generations (0⁺, 1⁺, 2⁺). New generation (0⁺) cohorts recruited into fishery in waves, from late summer to February. According to the von Bertalanffy growth curve, females grow larger than males, but there is a prominent seasonal growth oscillation in both sexes (females: CL_∞ = 62.48, K = 1.15, C = 0.87, WP = 0.16, Rn = 0.170; males: CL_∞ = 47.78, K = 1.28, C = 0.97, WP = 0.12, Rn = 0.205). Growth performance indices (φ′, φ) and longevity were in favor of females. K values for both sexes in Thermaikos Gulf are the highest reported for the species, suggesting a higher growth rate and a lower longevity. Estimated values for total, natural and fishery mortality were greater in males. In both sexes, an exploitation rate E > 0.5 was found, implying an intense fishing impact on M. kerathurus stock in Thermaikos Gulf. Intense exploitation in other parts of the Mediterranean and eastern Atlantic, along with the replacement of the species by Eritrean penaeid prawns in the eastern Mediterranean, has resulted in a severe reduction in catches, in most countries. Thus, existing stocks of M. kerathurus should be considered as potentially endangered, and species-specific initiatives towards sustainable management of this resource should be implemented.     

Age determination and growth of eel,Anguilla anguilla (L.), in lake Fertő Hungary

Ground and polished otolith sections, 0.2 mm thick, were produced from both sagittae of each fish, and repeated readings of the growth marks resulted in more accurate estimates of fish age. Supernumary zone formation in eel otoliths was a common phenomenon. The growth in length of the eels was accurately described by Bertalanffy's model using back-calculated lengths. Values of L_∞ = 1459 mm, K = 0.058 and t₀ = −0.869 years were determined. Mean incremental growth was calculated as 5–9 cm per year, showing that length increases rapidly with age. However, the growth of the eel population in Lake Fertő has become stunted, probably due to overstocking since 1975.     

Otolith biochronologies as multidecadal indicators of body size anomalies in yellowfin sole (Limanda aspera)

Dendrochronology (tree‐ring analysis) techniques have been increasingly applied to generate biochronologies from the otolith growth‐increment widths of marine and freshwater fish species. These time series strongly relate to instrumental climate records and are presumed to reflect interannual variability in mean fish condition or size. However, the relationship of these otolith chronologies to fish somatic growth has not been well described. Here, this issue was addressed using yellowfin sole (Limanda aspera) in the eastern Bering Sea, for which a 43‐yr otolith chronology was developed from 47 otoliths and compared with body size for 6943 individuals collected in 1987, 1994, and 1999 through 2006. Among several metrics of size normalized for age and sex, average body mass index (defined as weight/length) had the strongest relationship to the otolith chronology, especially when the chronology was averaged over the 5 yr preceding fish capture date (R² = 0.88; P < 0.001). Overall, sample‐wide anomalies in otolith growth reflected sample‐wide anomalies in body size. These findings suggest that otolith chronologies could be used as proxies of body size in data‐poor regions or to hind‐cast somatic growth patterns prior to the start of fisheries sampling programs.     

Age and growth of sea perch (Helicolenus percoides) from two adjacent areas off the east coast of South Island,New Zealand

A validated ageing methodology using otolith thin sections is presented for sea perch (Helicolenus percoides) in two adjacent areas off the east coast of South Island, New Zealand. Oxytetracycline marking of two adult fish held in captivity for 1 year suggested that a single dark growth increment formed during winter, commencing May or June. The annual formation of growth increments was confirmed by the observed progression of year classes in comparable samples from three different years, and the progression of length modes in several consecutive years that matched the estimated growth curves. Otolith interpretation was difficult because of a central dense region and the presence of many fine bands within each growth increment, but the latter could be counted, and it is considered that a validated ageing procedure is presented. Von Bertalanffy growth parameters were calculated for east coast South Island (ECSI) and Chatham Rise males and females. In both areas the growth rate of males is slightly but significantly faster than for females. Growth is relatively slow throughout life. From the maximum observed ages for ECSI and Chatham Rise fish of 35 and 59 years, the respective natural mortality rates are estimated to be 0.12 and 0.07 year^?1, but the most plausible value for the species is likely to be at the lower end of this range. Some stock differentiation between the two areas is indicated, based primarily on differences in length-frequency distributions implying different patterns of year class strengths, but also on apparent differences in growth rates between areas. This supports the present management regime of separate commercial catch quotas.     

Seasonal changes in otolith and somatic growth in age-0 Pacific saury <Emphasis Type="Italic">Cololabis saira</Emphasis>

We evaluated the seasonal changes in otolith and somatic growth of age-0 Pacific saury Cololabis saira in 223 fish collected between June and November 2002. We calculated the age in days of each individual by measuring otolith growth increments under a scanning electron microscope. The age was correlated with body length and otolith radius. We also observed seasonal changes in the rate of increase in body length and otolith radius and in the pattern of otolith growth. Until August, both body length and otolith radius increased with age. Thereafter, the otolith radius continued to increase, whereas the rate of somatic growth decreased. As a result, the ratio of otolith radius to body length increased. After August, the percentage of otoliths with unreadable increments on their edge increased due to the formation of hyaline zones. Otoliths grew both radially and in thickness until July, but gradually stopped growing in thickness after August. Beginning in October, more than 80% of otoliths only grew radially. After August, the otolith not only continued growing but the morphological growth pattern also changed.     

Evaluation of body weight and color of cultured European catfish (Silurus glanis) and African catfish (Clarias gariepinus) using image analysis

Two cultured catfish species (European catfish Silurus glanis, and African catfish Clarias gariepinus) were evaluated for their weight estimation and colors by image analysis. A total of 60 whole fish from each species were first weighed, and then their pictures taken by a digital camera in a light box. Length, weight and color of all fish were determined by image analysis and results were compared between the two fish. Fish weight ranged from 7.4 to 39.61 g and 25.71 to 93.91 g for European and African catfish, respectively. Weight (W) vs length (L) data were fitted linear (W = A + BL), power (W = A L^B) and second order polynomial equations (W = C₀ + C₁ L + C₂ L²). The R² values ranged from 0.835 to 0.974. For the W vs view area (V) relationship, the same equations were used. The R² values for these equations ranged from 0.927 to 0.972. No significant difference was found between the average color values according to the L*, a* and b* distributions for both fish species (P > .05). Image analysis can easily determine length, view area, and color of fish and help in developing W vs L, and W vs V relationships.     

Sexual dimorphism of fast muscle fibre recruitment in farmed Atlantic halibut (Hippoglossus hippoglossus L.)

Commercially farmed Atlantic halibut (Hippoglossus hippoglossus) were reared at the Aga Marin's facility located on Dønna (Norway) under ambient environmental conditions in duplicate 15 × 15 × 8 m netpens (May 2004 to May 2005). Twenty fish were sampled five times over a twelve month production period during which time the average body weight increased from 1.26 to 2.08 kg (n = 100 fish). Body mass, fork length (L_F), and the number and size distributions of fast muscle fibres were determined in male and female fish. All males matured during the autumn whereas no maturation was observed in females. From the point of maturation females had superior growth performance to males and body mass and the total cross-sectional area of muscle were 1.4-fold (P < 0.05) and 1.3-fold higher (P < 0.01) respectively by May 2005. The total number of fast muscle fibres per trunk cross-section at 0.55 L_F was 24.5% higher in females (7.58 × 10⁵) than males (5.80 × 10⁵) prior to sexual maturation. In females, muscle fibre recruitment slowed with short days and low water temperatures (< 6.5 °C), but had increased to 1.01 × 10⁶ by May 2005 (P < 0.001). In contrast, there was no growth and no increase in muscle fibre number in males following the onset of maturation. The distribution of muscle fibre diameters prior to maturation in males was also significantly different between male and female fish matched for L_F. The results illustrate a sexual dimorphism of muscle fibre recruitment patterns in Atlantic halibut and highlight the adverse affects of sexual maturation in males on muscle growth.     

Small-scale spatial variation in the population structure of vermilion snapper (Rhomboplites aurorubens) from the northeast Gulf of Mexico

This study estimated the variation in demographic parameters in vermilion snapper, Rhomboplites aurorubens, on a small spatial scale (i.e., tens of kilometres). Vermilion snapper were collected from seven reef sites in the northeastern Gulf of Mexico using hook and line. Sagittal otoliths were collected from vermilion snapper sampled over a 2 years period. Vermilion snapper were assigned ages from 1 to 14 years and were assumed to be fully recruited to the sampling gear by age 4 or 5 at most reef sites. Significant differences were noted in mean total length and age by reef site, depth zone and distance from shore. The overall sex ratio of vermilion snapper favored females (1.6:1) with no significant difference in this ratio for fish collected during spawning months versus non-spawning months, depth zone or distance from shore; however, there were significant differences in sex ratios by site. Differences were noted in growth by reef site, depth zone and distance from shore using size at age and in reef site using otoliths weight at age. A middle depth site consistently indicated faster growth than all other sites. Von Bertalanffy growth curves for males and females were different, however the growth coefficient (k) was not. Mortality rates did not differ by site, depth zone or distance from shore. The results of this study underscore the importance of spatial scale for understanding the dynamics of reef fish populations.     

Age and growth during immature stages of the mangrove red snapper Lutjanus argentimaculatus in waters around Ishigaki Island, southern Japan

Age and growth during immature stages of the mangrove red snapper Lutjanus argentimaculatus were examined using 129 sectioned otoliths of fish collected in rivers and coastal areas around Ishigaki Island. Monthly changes in the marginal growth index indicated that ring marks (inner edge of opaque zone) are formed once a year around May. Estimated ages of the sampled fish ranged from 0.2 to 4.5 years. The proportion of mangrove red snappers collected in each sampling set in the rivers was associated with age, namely, the older the fish, the smaller the proportion. This result suggests that the mangrove red snapper gradually moves from the river habitat to coastal areas with increasing age between 1 and 3 years. The relationship between standard length (Y; cm) and age (X; year) was expressed by the linear regression Y = 6.30X + 5.41. Both the somatic and otolith growth of age-one and age-two fish collected in coastal areas were faster than those of fish collected in rivers, suggesting that individuals with fast growth leave the rivers earlier than those with slow growth. Whereas the basic growth pattern obtained in this study is similar to that of the mangrove red snapper in waters around Great Barrier Reef, Australia, there is a clear difference in length of time spent in rivers between the two populations, probably associated with the difference in the scale of the rivers used as nursery grounds.     

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)]     

Growth of the golden grey mullet (Liza aurata (Risso)) in saltwater ponds during 1974

The growth rates of Liza aurata in saltwater ponds were measured during 1972, 1973 and 1974. The growth rate of L. aurata young of the year was 0.6–0.95 g per fish per day and that of fish in their second year of life was 0.85–1.0 g per fish per day.Body composition analyses were conducted on L. aurata in both the first and second years of life.A significant difference in length and weight was found between males and females of L. aurata in their second year of life.The results show that L. aurata can be stocked in saltwater ponds but that they will not be the main crop of fish.     

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.     

Seasonal change in the relationship between otolith radius and body length in age-zero Pacific saury <Emphasis Type="Italic">Cololabis saira</Emphasis>

We examined seasonal changes in the relationship between otolith radius and body length in age-zero Pacific saury Cololabis saira collected from June to December 2002–2004, based on 12,164 specimens. Results of the analysis using a generalized linear model indicated that there were differences in the intercepts among months, but no difference was seen in the slopes. In addition, post hoc analysis showed that the intercepts got larger as the month progressed from June to December. These results suggested that although the body length growth rate decreased, the growth of the otolith does not decrease to the same degree as the body after September, so the ratio of otolith radius to body length becomes larger as the months pass. Consequently, we consider that the seasonal change in relation between otolith radius and body length affects the back-calculation of body length based on otolith radius.     

Yield characteristics and morphometric relationships of giant freshwater prawn,Macrobrachium rosenbergii (de Man, 1879)

Meat yield of 233 individuals of giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879), and their morphometric relationships were examined. Morphometric parameters of different length and weight measurements were recorded for both the sexes separately and subjected to analysis. The meat yield of prawns was size and sex dependent with females showing significantly greater (P < 0.05) tail meat yield than males. The tail meat as a body weight percentage ranges from 26.12 to 40.75 and 32.97 to 42.11 in males and females, respectively. Much of the differences in yield are related to the size and weight of the head and claws. The head weight of males was observed to be higher compared to females in all the size classes. Regression slopes of total length versus body weight and total length versus head weight were significantly higher than critical isometric value indicating high positive allometric growth in both the sexes, with males showing significantly higher (P < 0.05) slope than females. The relationship parameters of total length versus tail weight and total length versus tail meat showed a positive allometric growth in females, whereas it is isometry and negative allometry in males. The morphometric relationship of tail length versus all weight measurements showed positive allometry and negative allometry in females and males, respectively.     

Using otolith increment widths to infer spatial,temporal and gender variation in the growth of sand whiting Sillago ciliata

Abstract Two methods of otolith increment analysis were used to describe spatial, temporal and gender variation in growth of sand whiting, Sillago ciliata (Cuvier), in four south‐east Australian estuaries. Mean annual standardised otolith increment widths were used as indices of individual lifetime growth rates, while raw otolith increment widths were used to describe variation in growth throughout the life of S. ciliata. Temporal variation in growth was observed at an annual scale, while spatial variation in growth was observed between estuaries. Growth rates increased significantly with decreasing latitude and greater mean sea surface temperatures. A divergence in growth rates between sexes was detected, with females growing faster than males after sexual maturity. This study highlights how otolith increment analyses can: (1) be used to analyse temporal trends in growth from a single sample and (2) provide insight into juvenile growth when samples have an absence of undersized fish.     

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.     

Size,growth, temperature and the natural mortality of marine fish

The natural mortality of exploited fish populations is often assumed to be a species‐specific constant independent of body size. This assumption has important implications for size‐based fish population models and for predicting the outcome of size‐dependent fisheries management measures such as mesh‐size regulations. To test the assumption, we critically review the empirical estimates of the natural mortality, M (year^?1), of marine and brackish water fish stocks and model them as a function of von Bertalanffy growth parameters, L (cm) and K (year^?1), temperature (Kelvin) and length, L (cm). Using the Arrhenius equation to describe the relationship between M and temperature, we find M to be significantly related to length, L and K, but not to temperature (R² = 0.62, P < 0.0001, n = 168). Temperature and K are significantly correlated and when K is removed from the model the temperature term becomes significant, but the resulting model explains less of the total variance (R² = 0.42, P < 0.0001, n = 168). The relationships between M, L, L, K and temperature are shown to be in general accordance with previous theoretical and empirical investigations. We conclude that natural mortality is significantly related to length and growth characteristics and recommend to use the empirical formula: ln(M) = 0.55 ? 1.61ln(L) + 1.44ln(L) + ln(K), for estimating the natural mortality of marine and brackish water fish.     

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.     

Age validation and growth variability of Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> off the Pacific coast of northern Japan

ABSTRACT:   This study examined age and growth of Japanese flounder Paralichthys olivaceus off the Pacific coast of northern Japan, and determined whether the growth patterns of male and female fish in northern (40–41°N) and southern (37–38°15'N) waters differ. In total 8095 specimens were collected between January 1999 and December 2005. Zonation consisting of opaque and translucent bands on the otolith was evident. Within each opaque band a thin and clear check (ring mark) was observed in all specimens examined. Monthly change in the frequency of appearance of a ring mark on the outer margin of the otolith indicates that ring marks form between July and August. The von Bertalanffy growth model showed a sexual dimorphism in growth, as females grew faster and reached a larger size than males. The growth patterns obtained by tracking the observed total length for monthly collections showed a rapid increase in total length between August and October. Spatial variation in the growth pattern of male and female fish between northern and southern waters was evident, as southern fish were significantly larger than northern counterparts during 1.25–3.00 years post hatch.     

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.