Studies On The Biology And Stock Assessment Of Placocheilus Cryptonemus

Placocheilus cryptonemus which belongs to Placocheilus of Cyprinidae, Labeoninae, is an endemic fish in the Nujiang River. They mainly inhabit the mainstream and branches of the middle and lower reaches of the Nujiang River. From October 2006 to July 2008,451 specimens were collected from Gongshan to Longling section in the the middle and lower reaches of the Nujiang River. This paper dealed with the biology and population ecology of Placocheilus cryptonemus. The main results are as follows.1. There were annulus on scale, otolith and vertebra, but otolith had more annulus readings than scale and vertebra, especially in an old age. Otolith was the best ageing material for P. cryptonemus.2. The body length range of P. cryptonemus was 36-125mm with an average of 76.9±16.5mm, and the body weight ranged from 0.7-32.8g with an average of 8.9±5.3g. The age composition was from 1+ to 7+, and the individuals of the preponderant age groups were 2+ to 5+, accounting for 90.61% of the total individuals.3. The relationship of body length and body weight for the female was W= 0.0001096 L2.5863, while it was W=0.00009067 L2.6158 for the male. The von Bertalanffy growth equation of body length were Lt=173.4486[1-e-0.1467(t-0.3380)] (for the female), Lt=97.6352[1-e-0.3070(t-0.2558)](for the male), and body weight growth equation were Wt=67.7669[1-e-0.1467(t-0.3380)]2.5863(for the female), Wt=14.5170[1-e-0.3070(t-0.2558)-]2.6158(for the male). The inflection point for the growth of female and male were 6.82 and 3.39 years, respectively.4. P. cryptonemus was an omnivorous fish species which mainly feed on the periphytic algae and organic debris. The feeding intensity of the fish changed with month, which was higher in July and lower in October.5. The sex ratio of the female to the male was 1.55:1. The minimum size of adult female was 68mm in length,7.4g in weight and 3.92% in the gonadosomatic index(GSI); while that of adult female was 64mm in length,5.2g in weight and 1.40% in GSI. The peak of GSI for ovaries and testises of adult was detected in July. The mean egg's radius was 2.49±0.36mm. P. cryptonemus were total spawners. The mean absolute fecundity was 130.9±65.3egg, and the mean relative fecundity was 1.37±0.62egg/mm body length and 10.95±5.15egg/g body weight. The regressive analyses showed that the individual absolute fecundity and relative fecundity per gram were significantly related with body weight, somatic body weight and gonad weight, and relative fecundity per millimetre was significantly related with body length, body weight, somatic body weight and gonad weight.6. Compared with the life history patterns of 11 kinds of fishes, the life history pattern of P. cryptonemus was studied using principal component method. The results showed that the life history pattern of P. cryptonemus tended to be r selection.7. Using the B-H model, it can be concluded that the exploitation rate was appropriate at present and the yield was close to maximum yield. To protect P. cryptonemus resource, the first capture age should be put off, and their habitat, feeding and spawning sites should be protected and preserved.