The morphological development and allometric growth patterns in the juvenile spotted seahorse Hippocampus kuda were studied under hatchery rearing conditions. Newborn spotted seahorses [mean ±s.d. standard length (LS) 9·33 ± 0·79 mm] were raised till the age of 124 days (119·35 ± 6·04 mm). Growth was characterized by three stages with two inflexion points occurring at day 21 and 76. The mean growth rates in the first, second and third stages were 0·68, 1·16 and 0·71 mm day−1, respectively. The growth rate was most rapid in the second stage and was probably influenced by a behavioural shift from pelagic to benthic form. The mass (M) and LS relationship was exponential (M = 7·14 × 10−6 LS2·76), but the slope, b = 2·76, reflected negative allometric growth. Sexes could be distinguished at c. 110 days, and the sex ratio was unbiased. The LS in males and females did not differ significantly. Morphological stageing series is proposed, which divides H. kuda juvenile development into eight stages based on the development of coronet, cheek and eye spines, keel and pigmentation. The morphometric ratios for all the body parts, except trunk length, showed considerable changes at a transition point occurring at c. 25 mm LS. The high proportional growth in head length, head depth, pectoral fin base length, dorsal fin base length, snout length, snout depth and eye diameter at the initial stages, and the abrupt increase in tail length only after the first 2 weeks, possibly reflect development priorities during early development where important organs are being developed first for the enhancement of juvenile survival.