This study aimed to determine a nutritionally adequate feeding protocol for Hippocampus hippocampus juveniles. In the experimental trial, seahorses were fed copepods from 0-7 days post-parturition (DPP) and, from 8-28 DPP, four dietary treatments: (copepods (control diet), microalgae-enriched Artemia with a DHA/EPA ratio of 2:1, microalgae-enriched Artemia with a DHA/EPA ratio of 2:1 along with 5% copepods, and with 10% copepods) were tested. Results showed that juvenile seahorses fed on copepods attained a significantly higher (P<0.05) growth performance (5.1 mg d-1) than fish-fed diets with 5% and 10% copepod inclusion, (3.09 and 3.07 mg d-1, respectively), and fish-fed enriched Artemia (1.83 mg d-1) which performed poorly. Data suggests that feeding copepods during the first 7 DPP promotes maturation of the digestive tract of juvenile seahorses, and the addition of a limited amount of copepods to the diet improves H. hippocampus juvenile growth performance when compared to the use of Artemia as a single diet due to the improvement of the essential fatty acid profile in the diets.

This experiment aimed to determine the temperature limits beyond which seahorse growth and reproduction become suboptimal due to climate change. Four temperatures (16, 20, 24, and 28°C) were tested to evaluate their effect on juvenile (1-56 days post-parturition (DPP)) and adult (one year old) seahorses. Additionally, the reproductive performance of adults was observed. Another experiment measured oxygen consumption (MO2) in the same age groups and temperatures. Adults showed significantly higher growth rates at 20 and 24°C compared to 16 and 28°C. Adult mortality rates were 0%, 0%, 6.2%, and 62.5% at the respective temperatures. Juvenile growth performance was higher at 20°C and 24°C but significantly lower at 16°C, with survival rates of 8%, 62%, 10%, and 0%, respectively. Oxygen consumption increased with age and temperature, ranging from 106.3±3.1 to 203.3±3.1 μmol O2/g BW/h at 16°C, and from 128.8±3.8 to 273.3±3.1 μmol O2/g BW/h at 28°C. The study highlights that juvenile and adult H. guttulatus have narrow thermal boundaries, beyond which reproduction, growth, and survival are seriously affected. Under climate change, the species appears unable to cope, potentially leading to their rapid disappearance.

This study investigated the effect of partially replacing fish meal with krill and copepod meals in inert diets, co-fed with shrimp, on the growth and nutrient digestibility of long-snout seahorse (Hippocampus guttulatus). A control diet (Diet 1) using raw starch and four experimental diets with similar protein (≈44.8%) and energy (≈15.1 MJ/kg) levels were tested. Diet 2 used fish meal as the sole protein source, while in Diets 3-5, krill and copepod meals replaced 44% of the fish meal. Seahorses fed Shrimp + Diets 2-5 showed significantly higher growth rates (P < 0.05) than those fed Shrimp + Diet 1, though there were no significant growth differences among Diets 2-5. Digestibility of dry matter (46.1% to 72.2%), lipids (73.3% to 85.5%), crude protein (89.8% to 95.8%), energy (82% to 92.2%), and phosphorus (28.7% to 64.4%) varied with diet, being consistently lower in seahorses fed Shrimp + Diet 1. As an agastric species, H. guttulatus did not exhibit impaired digestibility for any of the tested nutrients, minerals, or energy. This study suggests that crustacean meals can effectively substitute fish meal in inert diets for this species, contributing to the sustainability and optimization of captive seahorse husbandry practices.