How to Raise Seahorses? A Detailed Guide to Practical Breeding Techniques

The seahorse (Hippocampus sp.) is a valuable medicinal marine fish, long known as the "ginseng of the south." It was already praised in the Compendium of Materia Medica, having the effects of strengthening the body and tonifying the kidneys, strengthening the heart and inducing labor, dissolving phlegm and dispersing nodules, reducing inflammation and bringing down fever, and relieving pain and stopping bleeding. Its uses are wide, its market is large, and demand on the market exceeds supply. Moreover, seahorses grow quickly and have strong reproductive capacity, making them a breed with promising prospects for aquaculture. However, biological research on seahorses is still not sufficiently systematic; although breeding has been carried out in some areas, the breeding techniques are still very immature, and disease damage in particular is severe, so new experience remains to be gained through theoretical research and breeding practice.
　　
I. Biology of the Seahorse. The seahorse belongs to the order Syngnathiformes, suborder Syngnathoidei, family Syngnathidae, genus Hippocampus. It is a small fish of nearshore shallow seas, with many species and a wide distribution. In China's sea areas there are 6 species: the crowned seahorse (H. coronatus), the thorny seahorse (H. histrix), the great seahorse (H. kuda), the three-spot seahorse (H. trimaculatus), Kellogg's seahorse (H. kelloggi), and the Japanese seahorse (H. japonicus). The species mainly bred are the three-spot seahorse and the great seahorse, with the three-spot seahorse being bred the most.
(1) Morphological characteristics. The external morphology of seahorses differs only slightly among species. The three-spot seahorse generally has a body length of 10-17 cm. The body is laterally compressed, the head resembles a horse's head, and the abdomen protrudes noticeably. The trunk is seven-ridged and the tail is four-ridged; the tail is relatively long, gradually tapering, and curls toward the ventral side, used to grip seaweed and other objects for perching. The snout is slender and tubular, and the mouth is very small, located near the dorsum on the side of the head. The head and trunk form a right angle. The entire body of the seahorse has no scales and is completely enclosed by bony rings. The fish body is generally brown, but as the habitat environment changes, the body color can change accordingly and tend to match the environment. On the dorsal side of the 1st, 4th, and 7th body rings on the sides of the body there is a black round spot, hence the name three-spot seahorse, which is the main feature for distinguishing this species. The male fish has a special pouch-like organ on the ventral side of the tail, the brood pouch.
The great seahorse has a robust body shape, with a body length of 12-23.5 cm, a relatively swollen abdomen, and a relatively large head, approximately a right angle. The small spines are well developed, the snout is tubular and relatively thick and large, and the body color is relatively black.
The Japanese seahorse has a smaller body shape, with a body length of 4.5-9 cm. The snout tube is short and small. The abdomen is relatively swollen. On each ring of the body, the dorsolateral ridge spines are the most developed, and on the bony ring tubercles there are dendritic filamentous structures. When mimicry occurs upon encountering enemies, these filamentous structures increase.
(2) Ecological habits
1. Habitat and movement. Because of its mimicry adaptation characteristics, the seahorse also has relatively special habits. It likes to inhabit sea areas below the tide zone where algae or seagrass grow densely. It is very lazy by nature, often using its curled tail to cling to the stems and branches of seaweed, and sometimes also hangs upside down on floating seaweed or other objects, drifting with the waves. Even if it temporarily leaves the object it clings to in order to feed or for other reasons, after swimming a certain distance it finds another object to attach to. The seahorse's swimming posture is very graceful; the fish body stands upright in the water and relies entirely on the high-frequency wave-like swinging of the dorsal and pectoral fins (10 times per second) to swim slowly (only 1-3 m per minute). The seahorse is generally active during the day (morning and afternoon), and at night it is in a stationary state. When water quality deteriorates, oxygen is insufficient, or it is attacked by enemies, the seahorse often makes a clucking sound due to contraction of the pharyngeal muscles, which sends a "distress" signal to the breeder, but it also makes sounds when feeding on bait on the water surface, which should be distinguished.
2. Adaptation to environmental conditions.
Water temperature: The suitable temperature range for seahorses is generally between 12-32°C, with the optimum water temperature around 28°C. The adaptation of several seahorses to water temperature is shown in Table 2-8.
Salinity: The seahorse is a euryhaline fish and can live within a salinity range of 10-3‰. Newborn fry have poor adaptability to salinity and generally require salinity above 15‰. In a low-salinity environment for a long time, parent seahorses cannot reproduce normally; salinity above 10‰ is required.
Dissolved oxygen: Although the seahorse's activity level is relatively weak, its demand for oxygen in the water is very large. It generally requires dissolved oxygen above 3 ml/L. If dissolved oxygen is below 2.5 ml/L, the seahorse falls into an oxygen-deficient state, generally manifested as weakened appetite, floating at the surface, faster breathing with sound production, and even random collision, finally sinking to the bottom and dying. Parent seahorses during the brooding period and young seahorses have even higher oxygen requirements.
Light: The seahorse has certain requirements for light intensity. Too weak light is not conducive to the seahorse's activity and feeding; if light is too weak for a long time, the seahorse's eyesight declines and may even lead to blindness. But direct sunlight should also be avoided. If the light is too strong, algae multiply massively, often causing various diseases. Seahorses are phototactic, and seedlings in particular are more likely to gather toward light, so attention should be paid to deaths caused by local oxygen deficiency resulting from this. The suitable light range for seahorses is 3000-6000 lx. The water transparency is best at about 1.5 m. pH value: The suitable seawater pH value for seahorses is between 7.8-8.4.
3. Feeding habits. The seahorse swallows food by the extension and movement of the operculum and snout, and the size of the bait should not exceed the diameter of the snout. It has a certain selectivity for the type and freshness of bait. The seahorse's foraging visual range is only about 1 m, so bait should be cast where they often gather. In natural sea areas, seahorses mainly feed on small crustaceans, mainly copepods, barnacle larvae of cirripedes, shrimp larvae and adults, mysid shrimp, opossum shrimp, and gammarids. Under artificial rearing conditions, feeding opossum shrimp and krill gives the best results, followed by copepods and amphipods. Freshwater cladocerans can also be eaten, but care should be taken to avoid their rapid death in seawater and consequent water pollution.
The seahorse's food intake is closely related to water temperature and water quality. Within the suitable temperature range, when the water temperature is high, food intake is large and digestion is fast. When water quality is poor, food intake decreases and may even stop. Under normal conditions, the seahorse's daily food intake accounts for about 10% of body weight. The seahorse eats a large amount at one time and also has strong starvation tolerance; from newborn fry to adult fish, the starvation tolerance time can reach 4-132 days.
(3) Growth. The seahorse grows relatively quickly, and often after only a few months of rearing from fry production it can reach the size of the parent. Of course, this also varies greatly with species, and generally southern species grow faster. As for the lifespan of the seahorse under artificial breeding conditions, the great seahorse can reach more than 5 years, with a body length of up to 18 cm; the three-spot seahorse can reach more than 3 years; the Japanese seahorse more than 2 years, with a body length of about 8-9 cm.
1. Identification of male and female. The male seahorse has a brood pouch on the ventral side of the tail (located at the posterior end of the anus). This pouch is formed when the first reproduction period arrives by the joining of skin folds extending from the left and right of the ventral side of the tail, leaving only a small opening at the end. The end of the female's cloaca also swells more or less during the spawning period, forming a genital papilla. In addition, male seahorses are generally slightly larger than females.
2. Time of sexual maturity. The time of sexual maturity of seahorses varies with species, temperature, and bait conditions. The time for several seahorses to reach sexual maturity is generally 4-10 months for the three-spot seahorse, 9-12 months for the great seahorse, and 3-8 months for the Japanese seahorse. For the same species of seahorse, the time range of sexual maturity fluctuates relatively greatly, mainly related to water temperature. Taking the three-spot seahorse as an example, under suitable temperature conditions, fry born in May of that year can become sexually excited and reproduce by October (about 5 months). Those born in August often do not become sexually excited and reproduce until March-May of the following year. Other seahorses have similar situations.
3. Reproductive rate. The reproductive rate of seahorses differs greatly depending on species and nutritional conditions. Generally speaking, among adult seahorses with reproductive capacity, the three-spot seahorse and great seahorse account for about 20-80%; the Japanese seahorse is 50-80%. Under good rearing conditions, parent seahorses can reproduce several broods to more than a dozen broods per year (April-November, Guangdong). The number of fry produced per brood is generally from several dozen to more than a thousand; for example, the three-spot seahorse and great seahorse produce several hundred to 1,200 fry; the Japanese seahorse produces about several dozen to 400. The number of fry produced at the first sexual maturity of the seahorse is relatively small, and gradually increases afterward.
4. Breeding season and breeding method. The breeding season of seahorses in southern China is generally April-November, with June-September as the peak period, and the highest peak in July. The spawning period in the north is later and the time is also shorter. The water temperature of the breeding season is 20-28°C, and the peak period is 26-28°C. The fry produced at this time are of good quality, have a high survival rate, and grow quickly, while other seasons are relatively poor. Fry in the season when water temperature gradually rises are easier to rear than seedlings reproduced during the period when it falls, so from a production standpoint, early seedling rearing should be pursued each year to facilitate the growth of seahorses.
During the breeding season, sexually mature female and male seahorses often become sexually excited in the morning. At this time they chase side by side, swimming rapidly, and the melanin on the body surface contracts and fades, making them appear yellow-white. After excitement reaches its climax, the female and male fish approach each other, changing from side-by-side to swimming facing each other. The male seahorse bends toward the abdomen, causing the opening of the brood pouch to open, and at this moment receives the eggs sent by the female and fertilizes them inside the brood pouch.
5. Development. The fertilized eggs undergo 8-20 days of embryonic development inside the brood pouch, finally forming small seahorses that are produced from the male's brood pouch. Taking the Japanese seahorse as an example, its egg diameter is 1-1.5 mm. The newly hatched larva is about 3.5 mm, and body rings have not yet appeared. At 5 mm, segments begin to appear. Only when the larva is about 8 mm is it produced from the brood pouch. But the development of the segments is not yet complete, with only 4 body rings and 3 tail ring tubercles. The process of the seahorse giving birth to larvae is also very interesting. The male about to give birth tightly curls its tail around seaweed, swaying back and forth. Each time it leans up, it presses the small opening of the brood pouch open and sprays out a small seahorse, but sometimes it must lean back and forth more than a dozen times to produce one small fish. The newborn seahorse can immediately curl independently on nearby seaweed, and the male seahorse that has finished producing fry quickly becomes sexually excited again and mates.