Age Determination And Growth Characteristics Of The Anchovy In The Yellow Sea

In this thesis, methods for fish age determination were reviewed; the age determination procedure of anchovy (Engraulis japonicus) was described; the size characteristics of the saggita of anchovy and its usefulness for age determination were analyzed and discussed; the growth character of anchovy and its annual and seasonal variations were analyzed, and its responses to fishing pressure and environmental forcing were also discussed briefly. The main results are as follows.Based on literature research, methods for fish age determination were reviewed. Methods for fish age determination can be grouped into two categories, namely the direct identification methods and the indirect estimation methods. The direct method can be further divided up as in situ capture method, mark-recapture method and rearing method based on the difference in the source of the materials used for age determination; the indirect method are consisted of length frequency method, Saggita size method, eye lens size method, and radioactive isotope method. The basic principle, applicability, merits and drawbacks of these methods are summarized, integrated age estimation method based on the age structure and the size character of saggita are discussed.Based on binocular observations, the age structure of the saggita of anchovy is depicted and its characteristics for age determination summarized. The saggita of 0-year-old anchovy is almost round, small and thin, translucent; there is no annulus on it. The saggita of 1-year-old anchovy is more or less elliptical, growing bigger and thicker, semi- translucent, bifurcated and one end; there is one annulus on it. The saggita of 2-year-old anchovy is thick and ridgy, with radiating lines extended to the brim; there are two annuli on it. The saggita of 3-year-old anchovy is bigger and thicker still, ivory-white; there are more tines and three annuli on it. The desire and measures for quality control of age determination are also discussed briefly. Based on the samples collected from the Yellow Sea in October 2005 through September 2006, the metrical characteristics of the anchovy saggita are measured and analyzed. No significant difference (P=0.708) is found between the left saggita and right saggita in terms of both length and weight. The relationship between the length of the saggita and the total length of the fish is best described by power function. The two parameters a and b of the power function changes with time, and their directions of change are exactly opposite; a assumes its maximum and b assumes its minimum in April and May, and a assumes its minimum and b assumes its maximum in July and August. Both length and weight of the saggita are in linear relationship with the age of the fish. However, the lengths of the saggita in successive age groups are overlapped to such an extent that it can not be used to estimate the age of the fish. The weights of the saggita in successive age groups are less severely overlapped, and no significant difference is found between estimated age distribution based on the weight of saggita and the age distribution based on direct annuli reading, the weight of saggita can be an effective parameter to aid the age determination of anchovy when annuli can not be clearly read.Growth characteristics and its annual variation of the anchovy in the Yellow Sea and the influence of water temperature were analyzed based on biological data on the wintering anchovy obtained in January 2001, 2004 and SST at the Qianliyan marine environment monitoring station; the seasonal characteristics of the growth of anchovy were analyzed based on survey data obtained in June, August and October, 2000 and in January, March and May, 2001. The results are 1)the parameters in the Von Bertanaffy length growth equation, L∞, k and t 0are 190.1 mm, 0.47, -0.06 yr., and 172.7 mm, 0.61, -0.17 yr., respectively, for the wintering stock in 2001 and 2004; parameters in the weight growth equation, W∞, k and t 0are 45.4 g, 0.46, -0.11 and 35.5 g, 0.60, -0.21, respectively; the growth inflexion point ( t tp) sited at 2.35 and 1.72 year age. Relative to that in 2001, both length and weight growth rates by accumulated temperature were lager in 2004 for age 1 to age 3 fish; for age 4 fish, the length growth rates were similar while the weight growth rate decreased. 2) Concomitantly with stock recruitment and individual growth and death, marked seasonal characteristics were found in the length composition of the anchovy. Marked seasonality was also found in the Fulton's condition factor of the fish; the highest value, 0.82 was found before the peak-spawning season in May, the lowest value, 0.44 was found after the wintering season in March.