Growth and feeding behavior development of a marine ecotoxicology mode fish-medaka (Oryzias melastigma)

Aiming at the low survival rate of marine medaka (Oryzias melastigma), the experiment was carried out to understand the feeding behavior development of O. melastigma in early stage, so as to find a theoretical basis for breeding. The growth characteristics and feeding behavior of O. melastigma were observed and analyzed by feeding with Artemia nauplii during the first 90 days after hatching, by using a single camera, a waterproof-mirror and fish behavior analyze system. The results were as follows: its average growth rate in body length was 2.579%/d, and the relationship between body length and day-old age was y=3.132+0.383x−0.004x²+0.000 03x³, R²=0.98. Its larvae period could be divided into 3 stages (larvae stage was 0~10 d, juvenile stage was 11-30 d and young stage was 31-65 d) and 6 phases (pre-larvae was 0-4 d, post-larvae was 5-10 d, pre-juvenile was 11-18 d, mid-juvenile was 19-24 d, post-juvenile was 25-30 d, and young was 31-65 d) according to several indicators of the different feeding behavior. On the 4^th day after hatching (DAH), O. melastigma were fed with Artemia nauplii that hatched within 12 hours. And all larvae can feed on Artemia nauplii on 10th day after hatching (DAH). There was high mortality rate in larvae stage but the feeding ability was improved steadily. By the end of the period, the feeding success rate increased to 45%-55%, and the feeding efficiency reached 0.5-0.6 ind./min. At the juvenile stage (26-30 d), all indicators of feeding behavior greatly improved, such as the response time to Artemia was shortened and the distance was elongated, the feeding rate increased, and food intake also increased. At the same time, the success rate of feeding rose to a high level, up to 90%-95%. At the young stage, all indicators of feeding behavior were very close to the adult fish. The feeding efficiency reached more than 9 ind./min. Its feeding behavior development was mature, and feeding function tends to prefect at this stage. Experiments show that O. melastigma had a low feeding ability with a short response distance to Artemia nauplii, and the feeding success rate and feeding efficiency were still at a low level. The feeding success rate and feeding efficiency were gradually increased with its own development and feeding ability improving, and the survival rate tended to be stable. It may be an effective way to increase the survival rate of breeding when paying close attention to the changes in feeding behavior of O. melastigma through changing the feeding quantity and frequency to make a faster larvae fish transition to the juvenile period.