Studies on the Fisheries Biology of Pennahia Argentata in the North-Central Taiwan Strait and in Ariake Sound Japan

 by Attaqi

Ju, P.-L. et al. (2016). Age, growth, mortality and population structure of silver croaker Pennahia argentata (Houttuyn, 1782) and red bigeye Priacanthus macracanthus Cuvier, 1829 in the north-central Taiwan Strait. J. Appl. Ichthyol., 32: 652-660.

http://onlinelibrary.wiley.com/doi/10.1111/jai.13053/pdf

Yamaguchi. Et al. (2006). Reproductive cycle, sexual maturity and diel-reproductive periodicity of white croaker, Pennahia argentata (Sciaenidae), in Ariake Sound, Japan. Fisheries Research (82): 95–100.

  

ABSTRACT

       Fisheries biology of Pennahia argentata in the north-central Taiwan Strait and in Ariake Sound Japan was examined based on samples collected from two different area and objective studies. In the north-central Taiwan Strait between March-November 2006, a total of 994 specimens were collected from single trawler fishery. Fish size ranged from 58 to 267 mm in length and 5 to 410 g in total wet weight. Ages was determined or back-calculated between 0 to 5 years. The minimum size at first maturity for female 119 mm and 115 mm for male.  Compare with previous studies, P. argentata has decreased in recent decades, indicating that the populations were younger, smaller and earlier in sexual maturity. Meanwhile, Mortality coefficients were higher to be estimated total mortality (Z) was 1.7410, nature mortality (M) was 0.8690, fishing mortality (F) was 0.8720, and exploitation ratio (E) was 0.5009 indicated that fish have been overfishing. In Ariake Sound between September 2001 and Augustus 2002, a total of 421 females and between 14 July – 4 Augustus 2004, a total of 830 mature female were collected. The reproductive biology of P. argentata was studied by measurement of gonadosomatic indices (GSI) and histological examination of ovaries. Ovaries were classified into five maturity stages: (i) immature/resting; (ii) developing; (iii) maturing; (iv) ripe/spawning; (v) spent. The spawning season lasts from April to September with peak activity from May to August. Age at sexual maturity was assumed to be 1 year. The diel-changes in the proportion of females with postovulatory follicles and oocytes at maturation stage, most females spawned between 19:00 and 21:30 h.

Keywords: Fishery biology, Pennahia argentata, the north-central Taiwan Strait, Ariake Sound

  

Introduction

Pennahia argentata (Houttuyn, 1782) is a demersal fish belonging to the Sciaenidae family and inhabits sandy or muddy bottoms in the coastal inlets to a depth of 40~100 m. Distribution is from Tohoku, Japan to the Bohai Sea, the East China Sea, and the Indo-Pacific (Yamada, 2000). P. argentata have two common name are silver croaker or white croaker.

P. argentata is a part of the most common commercial fishery resources shared by Fujian and Taiwan provinces in the Taiwan Strait. (Fisheries Research Institute of Fujian, 1986; Island Joint Investigation Team, 1993). Meanwhile, P. argentata is one of the major species found in demersal fish assemblages off the coasts of Japan and is an important part of Japan’s commercial fisheries (Taki, 2000).

The objectives of this work were to: (i) estimate the age, growth, mortality of P. argentata in the north-central Taiwan Strait; (ii) the histology of ovarian tissue used to describe maturation, spawning season, age at sexual maturity and diel-reproductive periodicity in Ariake Sound.

Materials and Methods

Sampling area

In north-central Taiwan Strait

A total of P. argentata 994 specimens were randomly sampled monthly in 80~120 individuals from 10 stations from a trawler in March-November 2006 (Figure 1). The trawl net was 60 m in length and 125 m in entrance perimeter, with a 25 mm mesh size.

In Ariake Sound

Between September 2001 and Augustus 2002, a total of 421 females were collected from commercial bottom trawling and gill nets to describe maturation, spawning season and age at sexual maturity. Between 14 July – 4 Augustus 2004, a total of 830 mature females were collected from commercial bottom trawling to describe diel-spawning periodicity. All speciemens were collected in the middle part of Ariake Sound (Figure 2).

Methods Analysis

Age determination

The Fraser-Lee procedure (Lee, 1920) was used to back-calculate Standard Length (SL) associated with each annulus for each age-group: .

Growth

Length-weight relationship were estimated by the allometric equation (Sparre and Venema, 1992): .

Growth parameters were determined by the specialized von Bertalanffy growth model (von Bertalanffy, 1938): .

Because  and K may be correlated, the growth index x (Gallucci and Quinn, 1979) was used to compare different estimations of von Bertalanffy growth curves: .

Mortality

Total mortality coefficient (Z) was calculated (Ricker, 1975): .

The natural mortality (M) was estimated using an empirical equation relating M to , K and T (Pauly, 1980): . 

Fishing mortality (F) was estimated by subtracting from the total mortality: F = Z M.  The exploitation ration (E) was estimated (Ricker, 1975) from: E = Z/F.

Gonadal maturation, spawning season and age at sexual maturity

Gonadosomatic indices  were calculated to “assess maturity”. Maturity stages of ovaries were determined on the basis of the most advanced oocytes, and the occurrence of atretic oocytes and/or postovulatory follicles. The Spawning season was established on the basis of the mean monthly variation of GSI and ovarian maturity stages. Age at sexual maturity was estimated by the proportion of mature fish in each year class.

Diel-spawning periodicity

Diel-spawning periodicity was estimated by calculating the proportion of individuals with hydrated oocytes and postovulatory follicles in histological preparations of ovaries from all collected females.

Results

Size and age structure

P. Argentata Standard Length (SL) ranged from 58 to 267 mm (Figure 3). Age of P. Argentata were determined or back-calculated between 0 and 5 years (Figure 4).

Growth

Relationships between SL and otolith radius of the species was described as P. Argentata:  

Total wet weight-standard length relationships of P. Argentata  was calculated.

The von Bertalanffy growth (VBGF) equations were estimated to be The VBGF () of P. Argentata is the non-infection point curves which increase with age and tend to the asymptotic value. The VBGF () of P. Argentata is ‘S’ type curves and have points of inflection (Figure 5), indicating that the total wet weight increase with age experience by the Low – fast – Low, and then tend to asymptotic total wet weight.

Population structure

Population structures have changed in recent decades (Table 1). P. argentata mean SL decreased from 140.6 to 130.7 mm, and mean age from 1.42 to 0.99 years.

Table 1. Population structure, standard length, total wet weight and age changes
		Standard length composition (mm)			Total wet weight composition (g)			Age composition (years)
Species	Sampling years	Range	Dominant group	Mean	Range	Dominant group	Mean	Range	Dominant group	Mean	Authors
Pennahia argentata	1982	67-258	121-150	140.6	8-395	51-90	82.4	0-5	1	1.42	Zhang (1987)
	1994	65-216	111-150	132.2	7.5-242	41-90	64.7	0-3	1	1.09	Lu et al., (1999a)
	2006	58-267	111-150	130.7	5-410	45-90	61.4	0-5	1.0	0.99	Current study

Mortality

Survival (S) was broadly estimated using two methods from Heincke (1913) S₁ was 0.1655 and Robson and Chapman (1961) S₂ was 0.1858; we therefore adopted the average value of the two S to calculate total mortality (Z). Mortality coefficients (total mortality [Z] was 1.7410, nature mortality [M] was 0.8690 and fishing mortality [F] was 0.8720) and exploitation ratio (E) was 0.5009. The high F and E indicated that both species suffered great fishing pressure in this sea area.

Maturity stages

Oocyte development was classified into seven stages: (1) peri-nucleolus, nucleoli distributed around the inner margin of the nuclear membrane (Figure. 6a); (2) yolk vesicle, a large number of oil droplets present within the cytoplasm (Figure. 6b); (3) primary yolk, yolk globules first appear in the cytoplasm (Figure. 6c); (4) secondary yolk, yolk globules increased in size and number and occupied most of the cytoplasm (Figure. 6d); (5) tertiary yolk, yolk globules further increased in size and number, many oil droplets fused with each other (Figure. 6e); (6) migratory nucleus, the nucleus migrated from the center to a pole, and more oil droplets had fused (Figure. 6f); (7) maturation, a single yolk mass originated from the yolk globules (Figure. 6g). Newly formed postovulatory follicles (Figure. 6h) were found in many specimens with oocytes at yolk and mature stages. Degenerated oocytes were observed in specimens with oocytes at peri-nucleolus stage in September.

Figure 6. Histological observations of oocytes of Pennahia argentata. Scale bar=0.1 mm.

Spawning season

The GSI of females showed a distinct seasonal trend (Figure. 7). The GSI increased rapidly in May and declined sharply in September.

The mean frequency distribution of ovarian maturity stages is shown in Figure. 8 and also has distinct seasonal trend. Females at stage II, which commenced ovarian maturation, occurred in March. Females at stage III started to occur in April, and females at stage IV, having oocytes at maturation stage that were ready to be ovulated, were observed during May-August. Specimens with spent ovaries (stage V) were first observed in September. The spawning season lasts from April to September with peak activity from May to August.

Age at sexual maturity

Females at maturity stages II-V were estimated to be mature. The minimum size of female specimens collected from May to August 2002 was 139 mm in total length (). All specimens had mature gonads. In Ariake Sound, the total length at 1 year for white croaker approximates 160 mm in females (Higuchi et al., 2003). Accordingly, age at sexual maturity for females we collected was estimated to be 1 year.

Diel-reproductive periodicity

Females with hydrated oocytes occurred most frequently between 15:30 and 21:30 h throughout the sampling days, then decreased sharply after 22:00 h (Figure. 9). The occurrence of females with postovulatory follicles were most frequent during 19:00 – 21:30 h, just after the peak of spawning and decreased sharply afterward (Figure. 10). These data indicate that most females spawned between 19:00 and 21:00 h. 

Discussion

Growth and population structure

The growth performance index () was used to compare the growth rate in different areas. For P. argentata,  from Taiwan Strait was lower than in the East China Sea (Hu and Qian, 1989) and the northern South China Sea (Chen et al., 2010) but higher than in Japan Ariake Sound (Higuchi et al., 2003) and Omura Bay (Yamaguchi et al., 2004). Specific ecological factors, such as population density, environment temperature, and prey density, may cause growth parameters for P. argentata to vary in different sea areas.

Population structures have changed in recent decades. P. argentata mean SL decreased from 140.6 to 130.7 mm; mean age from 1.42 to 0.99 years. P. argentata was smaller in size and younger in age.

Over-exploitation: overfishing

The mortality coefficients (Z, F), especially F, increased in recent decades, indicating this species suffered from increased fishing pressure. The exploitation rate (E) in 2006 is 0.5156 reached or exceeded an optimally exploited value (E = 0.5: Gulland, 1971), indicating that the stocks had been overfishing.

Spawning season and age at sexual maturity

In the present study, all specimen was estimated on the basis of GSI and histological examination of ovaries. The spawning season lasts from April to September and is concentrated from May to August in Ariake Sound. Age at sexual maturity for females was estimated to be 1 year. Based on the diel changes in proportion of females with hydrated oocytes and postovulatory follicles, white croaker is suggested to spawn most frequently between 19:00 and 21:30 h.

In previous study of ovarian GSI, the spawning season of P. argentata was shown to lasts from March to July with peak activity from May to June in the northern part of the East China Sea and the Yellow Sea (Saishu et al., 1954) and from May to September with peak activity from July to August in the middle and southern parts of the East China Sea (Saishu et al., 1954). There are no differences in the spawning season between Osaka Bay (Yoshida et al., 1997) and Ariake Sound based on the mean monthly GSI.

It was estimated from GSI that female P. argentata reach sexual maturity at 1 year in Osaka Bay (Yoshida et al., 1997) and 2 years in the East China Sea (Saishu et al., 1954) and the Yellow Sea (Saishu et al., 1954). These variations in spawning season and age at sexual maturity of females may be an adaptation to local environmental conditions for each population.

Diel-reproductive periodicity

The diel period of peak spawning is often uniform within a taxonomic family (Ferraro, 1980). It was different between white croaker spawn between 19:00 and 21:30 h (Current study) late compared to Nibea albiflora in Ariake Sound spawn between 15:00 – 19:00 h (Takita, 1974).