The Reproductive Bionomics And Early Development Of Squalidus Argentatus In The Middle Reaches Of The Hanjiang River

Reproductive biology and early development of Squalidus argentatus Sauvage et Dabry was studied during May 2005 to August 2008 under an research on effects of NanShuiBeiDiao (water transfer from south to north) Centerline Engineering on the fish resources of the Hanjiang River and solution to fish resource protection in the middle and lower reaches of Hanjiang River. This research aimed to provide some useful information for rational exploitation and protection of fish resource after completing the water conservancy. The main materials and methods, results and conclusion are as follow:Samples were collected from nine sites around relevant cities and towns in the middle reaches of Hanjiang River from May 2005 to August 2008 especially in reproductive seasons. Samples were anatomized, weighted, observed and analyzed in lab and in sampling sites respectively, and sex gland was studied. From May to August in 2006, fish eggs (larvae) were collected by stationary section and flowing methods respectively, then eggs (larvae) cultivation, observation and analysis were conducted, and early development were drawn. The fish egg drift distance (S) was estimated by the product of time of embryo growth (T)and mean flow velocity of river (V), namely S = V·T; spawning sites were defined as the river segments where most fish spawn, and hydrology of spawning sites were reconnoitred in time. The spawning scale (M) was measured according to the egg number of fish captured in close growth period in sampling sites (m), the cross section discharge of water (Q), the flow velocity of net mouth (V), the density coefficient of fish egg in the cross section(C) and the area of net mouth (0.39), namely M = m·Q·C/0.39·V'. Physical and chemical factors in the sampling sites were measured according to Surface Water Quality Standards of People s Republic of China and Analysis Methods of Environmental Quality Standards for Surface Water. The results were shown as follows: 1) Physical and chemical factors in the middle and down stream of Hanjiang River are suitable for the reproduction of Squalidus argentatus; the growth and reproductive season of Squalidus argentatus are later than that of mainstream of the Pearl River and The Yangtze River; abundant nourishment in the middle of Hanjiang River provide good conditions for reproduction and growth of this fish; this species accounts for 28.4% of pint-sized fishes among the fish captured in the middle of Hanjiang River and is the dominant species in pint-sized fishes, possessing significant status in pint-sized fishes.2) Squalidus argentatus in the middle of Hanjiang River reproduce from early May to early August the body length of the spawning stock is 5.6-14.0 cm (7.82±1.36 cm) and body weight is 8.68-67.66 g (12.51±4.28 g). 95.91% samples of the spawning stock are 2-3 years old, 4.09% are 4 and over 4 years old, the average age of reproductive stock is 2.83±0.54 years old,♂:♀is nearly 1:1.3) The age at first maturity for both female and male is 2 years old. The body length, body weight, and gonadosomatic index (GSI) of the mature males are smaller than females'. The mature fish has distinct secondary sex characters, two equiponderant glands, and GSI increased from March, achieved the largest in July. Absolute fecundity (F) is 1732-32284 (4796±824) per fish and relative fecundity (F/W) is 223-477(373±42)/ g. The absolute fecundity increased with the age, and the relative fecundity decreased with the age. This fish belongs to single spawner.4) The gonadosomatic index of V stage is 31.45%-37.80% (mean 35.23±3.88%), egg diameter is 0.78-1.21 mm (0.98±0.22 mm). The oosperm has distinct double velamen after drinking, belonging to the viscous and drifting eggs. The ectoblast diameter is 3.60±0.42 mm and the endoblast diameter is 1.88±0.12 mm.5) From May to August in 2006, 152, 600 mature fish spawn 368 million eggs. There were seven spawning sites including Gucheng and Cihe, and more than half of spawning sections are located in the middle stream of Hanjiang River. The water temperature for spawning was 17.5℃-27℃and the spawning period was between the two flood peaks of high water after raining. Occurrence of spawning and its scale are related to the water temperature, flood duration, flow velocity and pattern of this river, and irrespective of the artificial flood caused by controlled flow of the dam.6) The early development of Squalidus argentatus is classified as four stages and fifty developmental periods, and is similar to the embryo development of the four major Chinese carps. However, There are some differences, such as the size of egg is 1/2-2/3 of major Chinese carps', Involute germ layer of gastrula stage was less, caudal vesicle formed before the auditory vesicle, embryonic development time is 3-5 h less than that of the major Chinese carps, mouth formed after the branchial arches appeared, there was no distinct eye xanthophore stage, swim bladder appeared after the formation of intestines, there are 37 pairs of myotome in juvenile stage.In conclusion, Squalidus argentatus is a kind of the preponderant spices among small-sized fishes which have large progenitive colony, excellent reproductive adaptability and capability, and is the only fish whose oosperm has distinct double velamen after watering among all fishes producing the drifting eggs in the middle of Hanjiang River. The spawning sites are widely distributed and the early development is similar to the cyprinid fishes, but distinct in some aspects.