Growth and reproduction of double-ended pipefish, Syngnathoides biaculeatus, in Moreton Bay, Queensland, Australia

Abstract

Life-history characteristics of the double-ended pipefish, Syngnathoides biaculeatus (Bloch), were investigated to determine growth rate, degree of sexual dimorphism, size at maturity, and reproductive biology. Growth rates of wild juveniles and adults calculated from monthly progression of length-frequency modes ranged from 0.8thinspmmthinspd-1 (fish lengths 120-145thinspmm standard length (SL)) in summer to 0.2thinspmmthinspd-1 in winter (185-200thinspmm SL). Growth of laboratory-reared juveniles up to 63thinspd old was greater, ranging from 0.8 to 2.3thinspmmthinspd-1. The von Bertalanffy growth constant K was estimated at 0.0076thinspd- 1, or 2.8thinspyear-1. Morphological differentiation between the sexes based upon abdominal pattern was possible for fish larger than 120thinspmm SL, with females possessing a zigzag pattern on the abdomen. The association between this pattern and sex was confirmed by histological gonad analysis. Males were significantly longer than females during four of seven seasons examined, and a 1thinsp:thinsp1 sex ratio was determined for all seasons except autumn when the ratio was female biased. The breeding season was marked by the appearance of pregnant males between October and April, and during courtship both species exhibited increased pigmentation. The minimum paternal size at maturity was 185thinspmm, the maximum length recorded 260thinspmm. Clutch size ranged between 60 and 200 eggs, with a mean of 153. Ovaries had a sequential pattern of egg development, resulting in egg batches that approximated the number of eggs carried by brooding males. Additionally, all eggs in a brood were at the same developmental stage. This suggests that one female provides all of the eggs for one male per breeding event in a monogamous mating system.