Back-calculated Standard Length Research Articles

Comparison of age and growth of grass and silver carp above and below Changzhou Dam in the Pearl River, China

The life cycles of potamodromous fishes are generally interrupted by the presence of a dam, and populations often display different life history traits between upstream and downstream. This study compared the age and growth rates of grass carp and silver carp above and below Changzhou Dam in the Pearl River. Standard length (SL) composition and back-calculated SL at ages one and two years were greater for grass carp upstream than for downstream individuals; and the length–weight relationship differed between upstream and downstream populations, while the sex ratio, age structure and growth were not significantly different. For silver carp, only SL compositions differed between upstream and downstream populations; sex ratio, age structure, SL-at-age and growth rates were similar. Mean SL-at-age and growth rates of both species were lower at high latitudes than at middle and low latitudes, and populations in the Yangtze River had greater mean SL-at-ages and faster growth relative to silver carp at low latitudes. There were no differences in mean SL or growth among populations at middle and low latitudes. For grass carp, age and growth varied with small-scale ecological processes and regions or latitude, while for silver carp, such variations were proportionate to latitude and the large-scale geographical range. This study provides not only guidelines for fisheries management and conservation of exploited potamodromous fishes, but also insights into the relationship between life history trait variation and adaptive capacity.

Growth variability of juvenile skipjack tuna (Katsuwonus pelamis) in the western and central Pacific Ocean

We examined growth rates of juvenile skipjack tuna using otolith daily increment analysis to clarify geographic differences in early-life stage growth in the western and central Pacific Ocean (WCPO). We used a liner regression model to analyze the relationship between standard length (SL) and age (in days). The slope of growth model was significant difference between regions. There were rapid increases in the otolith mean daily increment width of juveniles at 7 days after hatching (DAH) and 10 DAH in the Western Pacific Warm Pool (WARM) and North Pacific Tropical Gyre area (NPTG), respectively. These periods correspond to the timing at which larvae complete their digestive-system development and start the piscivory. We found significant difference in logarithmic back-calculated SL between WARM and NPTG at 3 DAH (p < 0.01). Mean growth rates until 10 DAH, when the larvae metamorphose into juveniles, were positively correlated with sea surface temperature (r = 0.52). These results indicate that geographic difference in the growth of juvenile skipjack tuna caught in the WCPO in boreal winter cause in the larval stage, and that these differences are related to sea surface temperature.

Life-history traits of Amur sleeper, Perccottus glenii, in the invaded Vistula River: early investment in reproduction but reduced growth rate

In recent decades, Amur sleeper is one of the most invasive fish species in Eastern and Central Europe. Generally, it is assumed that success of an invasive species can largely depend on the plasticity of its life-history traits, e.g., indicated by higher investment in reproduction in the initial stage of its invasion. On the other hand, such energy allocation to production of gonads should negatively impact somatic growth rate. The aim of this article was to explore this phenomenon in a non-native population of Amur sleeper inhabiting artificial reservoir on a large lowland river in Central Europe. Through analysis of the population age structure, sex-dependent growth rate and life-history traits we assessed investment in reproduction and its possible relationship with growth pattern as well as compared the results with literature data from native and introduced range. Samples collected monthly from April 2005 to March 2006 were used to estimate sex ratio, GSI, fecundity, eggs diameter frequency over the year, duration of spawning season, and mode of spawning. Age structure was calculated from scales and the same data were also used to back-calculate standard length (SL) at age. The population in the Włocławski Reservoir was represented by eight age groups, and its life span was one of the longest recorded both in its natural range and introduced areas. The weight–length relationship showed that the Amur sleeper grew isometrically and there was no difference between females and males. Although the Amur sleeper growth rate was relatively slow in the Włocławski Reservoir, its increment in the first year of life was comparable to that in other introduced areas and higher than in its natural range. The female age of maturation (1+) found in the reservoir was earlier than observed in its natural range as well as in most introduced areas (2+, 3+). Female length at maturation was similar to that reported elsewhere. The back-calculated standard length (SL) of females and males showed that in the first two age classes (1 and 2) males achieved larger SL than females. Meanwhile, at age 3, 4 and 5, females were larger than males but these differences were insignificant, except for class 5. For both sexes the average annual increment of SL decreased with age but in females the increment was always higher than in males (P < 0.05). The growth rate differences between females and males resulted possibly from their unequal investment in reproduction. Multiple spawning in the Włocławski Reservoir lasted from April to the end of August and was almost 3 months longer than in other regions. Thus, this higher investment in reproduction displayed by, e.g., earlier maturation of females and longer spawning season in the Włocławski Reservoir, may contribute to invasive success of Amur sleeper in newly colonized areas; however, the costs of this strategy result in slower growth in older age classes.

Age and growth of the mudskipper Boleophthalmus pectinirostris in Ariake Bay, Kyushu, Japan

Abstract By measuring the growth rings of the second pectoral radial bone, we estimated the age and growth of blue spotted mudskipper, Boleophthalmus pectinirostris, collected from mudflats at the mouth of the Tojin River running into Ariake Bay in Kyushu, Japan, between April 2001 and March 2002. We examined a total of 999 individuals ranging from 48 to 138 mm in standard length (SL). An additional opaque margin of radial bone was produced once a year, between September and November. The pattern of this increment was consistent with that in a previous study of a population in Ariake Bay, but differed from those of other studies in terms of the number of annual increments and/or the seasonal timing of the increment. The von Bertalanffy growth parameters derived from back-calculated and observed SL were as follows: back-calculated SL, L∞ = 116.3 mm, K = 0.799 year−1, and t0 = 0.70 year for males and L∞ = 109.5 mm, K = 1.097 year−1, and t0 = 0.55 year for females; observed SL, L∞ = 117.5 mm, K = 0.672 year−1, and t0 = 1.70 year for males and L∞ = 114.1 mm, K = 0.702 year−1, and t0 = 1.67 year for females. The maximum age was estimated at 7 years for males and 6 years for females. Compared with previous studies, the fish in our study had the slowest growth, smallest maximum size, and oldest maximum age in both sexes.

Three synergistic growth-related mechanisms in the short-term survival of larval Japanese anchovy Engraulis japonicus in Sagami Bay

The 'growth-mortality' hypothesis, which holds that larger and/or faster growing individuals will have a higher probability of survival, currently includes 3 functional mechanisms (hypotheses) in its theoretical framework: 'bigger is better', 'stage duration' and the recently proposed 'growth-selective predation', which are based on size, time and per se growth rate, respec- tively. Through otolith microstructure analysis, we tested these 3 synergistic growth-related mecha- nisms according to growth characteristics of the survivors vs the original population in the short-term (ca. 2 wk) survival process of larval Japanese anchovy Engraulis japonicus in the 'shirasu' (larval anchovy) fishing ground in Sagami Bay, Japan. Back-calculated standard length (growth trajectory) and growth rate (growth history) were compared between the survivors (SV) captured on 18 July 2001 and the presumed original population (OP) captured on 1 and 5 July 2001. The larvae from SV were consistently smaller than the larvae from OP until at least the start of the ca. 2 wk survival pro- cess (1 July). Daily growth rates, however, were higher for SV than for OP at least at the start of the survival period. Therefore, faster growing individuals survived even if they were smaller than slower- growing conspecifics. This was probably mediated by predation. Growth histories were generally similar between the metamorphosing larvae and non-metamorphosing larvae older than 40 d, the minimum age for metamorphosis, except for the period immediately after hatching. As such, we failed to detect a clear relationship between growth rates and the timing of metamorphosis (stage duration) as a whole. The results supported and extended the 'growth-selective predation' hypothe- sis but not the 'bigger is better' hypothesis. The 'stage duration' hypothesis was not unequivocally supported by the present findings.

Population structure and feeding characteristics of Volga pikeperch, Sander volgensis (Pisces, Percidae), in Lake Balaton

Growth, population structure, abundance, production, and feeding of Volga pikeperch were studied in Lake Balaton. The population was mainly comprised of age-groups 0+ (59%) and 1+ (18%), while the total share of age-groups 6+ and older was less than 1%. Mean back-calculated standard lengths for age-groups 0+-9+ were 67, 123, 144, 196, 233, 256, 283, 316, 350, and 369 mm, respectively. The instantaneous rate of growth in weight was lower at age 2+ than it was at age 3+ and 4+, suggesting unfavourable conditions for Volga pikeperch 120-160 mm in size. In autumn, the average abundance of Volga pikeperch was 34 ind. ha -1 , the biomass 1.04 kg ha -1 , and the production 0.76 kg ha -1 in the SW basin of Lake Balaton. Based on the diet, three phases can be distinguished during the ontogeny. Zooplanktivory is characteristic for the early juvenile stage up to 50 mm in size. At the size of 50-150 mm the diet becomes heterogeneous, consisting of zooplankters, benthic invertebrates, and fish. The third phase is the piscivory which becomes a determinant at over 150 mm in size. In this phase cannibalism was also significant, as 21.9% of consumed fish were conspecifics.

Reproductive-timing-dependent alternation of offspring life histories in female threespine sticklebacks

Relationships between reproductive timing of spawners and timing of hatch and age at maturity of their offspring were examined in fluvial threespine sticklebacks, Gasterosteus aculeatus. Some age 2 and all age 3 females matured in this age-structured population, with only a few females reproducing over two successive breeding seasons. Age 2 females spawned over the relatively long breeding season (March-August), whereas age 3 females spawned mainly early in the season (March-June). Although the standard length of mature age 3 females was greater than that of age 2 females, the back-calculated standard lengths of the former were always shorter than those of the latter at an equivalent age, the most distinct differences being apparent in young of the year. Analysis of daily otolith increments showed that the earlier the young of the year were born, the larger they were at the end of the growing season. As a result of these findings, age 3 females can be expected to produce offspring that will mature at age 2, whereas the offspring of late-spawning age 2 females are more likely to mature at age 3. Therefore, a partial alternation of life histories between generations is thought to occur.

Age and Growth by Scale Analysis of Pomacanthus imperator (Teleostei: Pomacanthidae) from Dongsha Islands, Southern China

A total of 200 specimens of Pomacanthus imperator from Dongsha Islands (South China Sea), were examined for age and growth. Scale radial length (R) is linearly proportional to standard length (L) and their relationship can be expressed by the formula L=3.6+43.8R. Relationship between standard length and body weight (W) can be expressed by the formula W=1.63×10−4L2.77. Mean standard lengths of each age group were back-calculated from scale annuli readings and were found to be 66.4, 94.2, 120.7, 133.9, 145.6, 157.9, 170.7, 188.0, 200.9, 217.6, 222.0, 242.8, 253.0, 268.1, 277.0 and 293.0 mm for age classes 1 through 16, respectively. The von Bertalanffy parameters L∞, K, and to fitted to back-calculated standard lengths were, respectively, 411.9 mm, 2852.1 g, 0.067 years−1, and −0.91 years. Marginal increment analysis indicated that annulus formation takes place between January and March.

On the Age and Growth of the Labroid Fish Halichoeres poecilopterus from the Seto Naikai, Japan.

The age and growth of the labroid fish Halichoeres poecilopterus from the Seto Naikai were estimated by examining the scales based on the specimens collected from the Seto Naikai from 1981 to 1984. With respect to the results of our study, one annulus of each scale is formed once a year in the hibernating period from January to April. This species spawns in early summer from late June to July, based on the temporal fluctuation in gonad index of the female. At the age of 1, 2, 3, 4 and 5 years old, the fishes are 61, 86, 106, 124 and 140mm in standard length, respectively, as estimated by the marginal growth indices. The general growth of the fish is presented by the following formula described by BERTALANFFY: Lt(mm)=234.8{1-e-0.151(t-0.986)}. The length(mm)-weight (g) relationship of this species is given by the formula, W=4.886×10-6L3.280. Consequently the asymptotic weight is estimated as 291.6g. The mean standard length of the immature yearlings collected in December, 1983 and 1984, were 42.4 and 42.3mm, respectively. The back-calculated standard lengths of yearling fishes in early summer are expected to be 44.7mm in December. The back-calculated standard lengths of the yearling are almost equal to their actual standard length.