Allometric growth pattern and development of Monopterus albus at larvae and juvenile stages

Monopterus albus is a tropical and warm temperate fish, which is an important freshwater economic fish in China, and has the phenomenon of natural sex reversal. It initially develops into female, with small individuals and limited number of eggs. Therefore, it is difficult to carry out large-scale artificial breeding. So far, the research mainly focuses on the regulation of sex reversal, nutritional requirement, disease control, artificial reproduction and cultivation. However, few studies focuses on the characteristics of growth and development at larvae and juvenile stages. The aim of this study was to explore the growth characteristics and allometric growth of M. albus in the early development stages. In this study, the growth and development characteristics, 1 to 30 days post hatching (dph), were described, including total length, body weight, snout length, eye diameter, head height, head length, trunk length, tail length and body height. The results indicated that the yolk sac of the newly hatched larvae of M. albus was large and completely disappeared at 10 dph. A pair of pectoral fins were existed in the early development stage of M. albus, became smaller gradually and disappeared completely at 9 dph. The increase of the total length showed S-Curve, which could be divided into three phases, and the growth rate had significant difference at each phase. The increase of body weight could be divided into two phases, and the growth rate also had significant difference at each phase. The optimal length-weight relationship of larvae and juveniles was y=0.006e^0.050x. The relationship between various functional organs and the full length was analyzed by SPSS 27.0.1 and Origin 2022 software. The results showed the allometric growth of important functional organs exists in larvae and juvenile stages of M. albus. There was no growth inflection point in snout length, eye diameter and head length from the day hatched to 30 dph, and the allometric exponents were 0.844, 0.615 and 0.878, respectively. Head height appeared growth inflection points at 10 dph, and the allometric exponents before and after it were 0.407 and 0.557, respectively. Trunk length appeared growth inflection points at 19 dph, and the allometric exponents before and after it were 0.964 and 1.212, respectively. Tail length appeared growth inflection points at 24 dph, and the allometric exponents before and after it were 1.046 and 1.156, respectively. Body height appeared two growth inflection points at 11 and 22 dph, and the allometric exponents were -1.271, 1.412 and 0.709, respectively. The growth inflection points of various functional organs were different, which was coincident with the characteristics of growth, food intake, movement, and so on. These results have important guiding significance for the large-scale seed rearing and sustainable farming industry in M. albus.