| Coilia mystus is a main economic fish in the Yangtze estuary,however, since the overfishing, environment pollution and hydroeletric project, the resources of increasingly recession. In this research, we took C. mystus collected from the coastal waters of the Yangtze estuary from April to September, 2014 as research object. We studied their individual fecundity, spawning period, the distribution of larvae and juveniles and related environmental factors. 1. Individual fecundity of Coilia mystus in the Yangtze estuaryBetween April and August 2014, the matured female C. mystus specimens were collected in waters of Q ingcaosha(31°25′N 121°43′E), Dongwangsha(31°36′N 121°57′E) and Tuanjiesha(31°25′N 121°53′E) in the Yangtze River estuary. The body length(L), body weight(W), ovary weight(W1), and other biological indicator indexes of 124 female individuals with ovary maturation developed to IV stage were measured and their ages(A) were identified through the characteristics of sagittal otolith. The gonadosomatic index(GSI), condition factor(CF), the individual absolute fecundity(F) was obtained, relative fecundity of body length(FL) and relative fecundity of body weight(FW) were calculated. The relationship between individual fecundity and biological indicator indexes of Coilia mystus were studied.The results showed that the specimens ranged in age from 1 to 3 years old. The individual absolute fecundity(F) varied from 3146.2 to 33237.0 eggs, and the individual relative fecundities(FL) and(FW) ranged from 27.7 to 185.7eggs×mm-1 and 366.5 to 1614.2 eggs×g-1 respectively. The egg diameter ranged from 0.484 to 0.928 mm. According to the correlation analysis, the correlation coefficients between F or F L and body length(L), body weight(W), net body weight(W0), ovary weight(W1), gonadosomatic index(GSI) and age(A) of the individuals reached very significant level(P<0.01). Otherwise, FW is positively related to ovary weight and gonadosomatic index(P<0.01). Regressive analyses showed that the best fitting equations of F or FL and each of body length(L),body weight(W), net body weight(W0),ovary weight(W1), gonadosomatic index(GSI) and age(A) were the power function, while the S-curve equation and power function were the best fitting equations of FW and ovary weight(W1) and FW and gonadosomatic index(GSI). Moreover, canonical correlation analysis showed that F was related to ovary weight(W1) and FL was mainly dependent on the body shape of fish. The egg diameter ranged from 0.484 to 0.928 mm. It is speculated that C. mystus spawns once a year based on the distribution of egg diameter. 2. The daily age, spawing date and growth of Coilia mystus in the Yangtze estuaryFrom April to September, 2014, 180 specimens of C. mystus larvae and juveniles selected at random, which collected in waters of in the Yangtze River estuary. Sagittal otolith were removed from the specimens, the daily age, spawing date and growth of Coilia mystus were studied. The results showed that there was only one nucleus and one primordium on the sagittal otolith of Coilia mystus, with primordium was 15.90±1.85 μm in diameter. The diameter, ratio of length to width increased and the shapes shifted from circle to ellipse type with daily age. The body length varied from 4.21 to 26.20 mm, and the daily age ranged from 5 to 48 d.The individual absolute fecundity(F) varied from 3146.2 to 33237.0 eggs, and the individual relative fecundities(FL) and(FW) ranged from 27.7 to 185.7eggs×mm-1 and 366.5 to 1614.2 eggs×g-1 respectively. Back-calculated from sampling time and daily age, the spawning period ranged from May 16 to August 19. There were two main spawning periods, one ranged from late May to mid-June and another one ranged from mid-July to mid-August. There was significant associated between length diameter of otolith and body length, and the relationship was power function. The binomial relationship between length diameter of otolith and daily age was significant. And a liner function was the best model in the fitting between body length and daily age. 3. Preliminary assessment of habitat suitability of Coilia mystus nursery area inthe Yangtze estuaryTo assessment the habitat suitability of Coilia mystus nursery area in the Yangtze estuary, the paper selects 4 indicator factors, such as salinity, turbidity, water depth and temperature. The index of habitat suitability curves with indicator factors were protracted, and the HSI of Coilia mystus nursery area at each sites were calculated. Then the planar distribution of habitat suitability index was protracted.The result showed that the main habitat condition of Coilia mystus nursery area were:salinity 13 to 19, turbidity 45 to 140, water depth 9 to 11 m, temperature 24 to 25.2℃. According to he planar distribution of habitat suitability index, the HSI was higher in the water of the North Branch of Chongming Island, and indicated that the North Branch of Chongming Island is the nursery area of Coilia mystus. |
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