Big-belly Seahorses (Hippocampus abdominalis) are found in both South-East Australian and New Zealand waters, typically inhabiting shallow environments such as large rock pools at low tide.

These types of habitats are preferred as they are the most productive for the seahorse’s ambush predation strategy[8] Juveniles are pelagic or attached to drifting seaweed, and adults feed on minute crustaceans like copepods and amphipods.

These seahorses are often observed in groups at night and can attach to sponges, colonial hydroids, or man-made structures such as jetty piles in deeper water.

[10] Juvenile and adult big-belly seahorses, when given a choice, prefer vegetated areas (even with artificial seagrass) over open water.

Increasing vegetation density from low to medium habitat complexity positively impacts the capture success of both juvenile and adult big-belly seahorses who are feeding on mysid swarms.

[9] The number of unsuccessful attacks for juveniles, is possibly due to high vegetation density disrupting prey swarm structures, which can form defensive formations.

[13] While early juveniles are pelagic in their first month of life, they display attachment to substrates, suggesting a potential preference for specific characteristics.

This aligns with earlier findings that emphasize the need for appropriately sized substrates in seahorse rearing to promote optimal distribution and minimise stress.

Both sexes tend to have home ranges that overlap with 6–10 members of the opposite sex; this suggests that mate availability is not a limiting factor for monogamy[9] Body size does not significantly affect home range size or movement patterns of the big-belly seahorse, this challenges the idea that larger individuals would have larger space requirements due to foraging needs or mate searching.

Physical interference, such as tail-grasping during feeding, hinders growth and survival at higher densities, with crowding negatively affecting juvenile development.

This highlights the importance of managing stocking densities in aquaculture to promote healthy growth and reduce competition during feeding[17][8] Big Belly Seahorses show no typical stress responses (e.g., plasma cortisol, glucose, or lactate) after brief acute stress (60 seconds of air exposure), indicating a lack of adrenergic activation.

[19] Adult seahorses eat 30 to 50 times a day if food is available; due to their slow consumption they must feed constantly to survive.

[20] Big-belly seahorses do not have a stomach or teeth, so they feed by sucking small invertebrates in through their bony tubular snouts with a flick of their head.

[25] Female, male and juvenile big-bellied seahorses make "click" sounds while feeding, often paired with a head movement called a "snick".

[26] Studies showed that the diet of adult wild big-belly seahorses when living in shallow subtidal macroalgal primarily consists of crustaceans.

However, smaller seahorses were found to consume more crustaceans than larger ones, due primarily to the higher proportion of amphipods in their gut contents.

[27] Further research into the impact of varying feed ratios of frozen mysids (Amblyops kempii) on their growth and survival revealed no significant differences in standard length after three months.

Therefore, it is recommended to maintain a daily feed ratio of 5–10% wet body weight of frozen mysids for optimal growth in big-belly seahorse aquaculture.

[28] Similarly, when fed diets consisting of live enriched Artemia (brine shrimp), frozen mysids (Amblyops kempi), or a combination of both there were no observed differences in seahorse length, wet weight, condition factor, or food conversion ratios among the treatments.

Frozen mysids are still considered a viable alternative to live Artemia in seahorse diet in aquaculture, potentially reducing costs and improving survival rates in the aquarium trade.