Seahorse Development

From Embryology

Introduction

Newborns of three syngnathid species (A) N. ophidion, (B) S. abaster, and (C) H. abdominalis. Scale bars are 2 mm.[1]

Hippocampus (Greek, ippos = horse; kampe = curvature)


Actinopterygii (ray-finned fishes) > Syngnathiformes (Pipefishes and seahorses) > Syngnathidae (Pipefishes and seahorses) > Hippocampinae


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Seahorse Development

Some Recent Findings

  • Early development of the longsnout seahorse Hippocampus reidi (Syngnathidae) within the male brood pouch[2] "Fertilized and unfertilized eggs and embryos of the longsnout seahorse Hippocampus reidi were collected at different stages of development and provided the basis for a description of morphological development from fertilization until release from the paternal pouch. Images of fertilized eggs, as well as their rupture after a few minutes in seawater are reported for the first time. The yolk sac transitioned from ovoid to spherical shape and was reabsorbed progressively until release. The tail began rising from the surface of the deuteroplasm while embryos were in the egg envelope. Embryos lacked a primordial fin fold and developed some species characteristics, such as rays in the dorsal fin, before resorption of the yolk sac. At release, juvenile seahorses were in an advanced stage of development even if they lacked important adult characteristics, such as ring plates and coronet. The tail was not prehensile in juveniles at release; a small caudal fin was present, although this fin is lost in adults."
  • Development of short-snouted seahorse (Hippocampus hippocampus, L. 1758): osteological and morphological aspects[3] "Information about early development after male release lags behind studies of juveniles and adult seahorses, and newborn seahorses, similar in shape to adults, are considered juveniles or fry. During early life, Hippocampus hippocampus present behavioural (shift in habitat, from planktonic to benthic) and morphological changes; for this reasons, the aims of this study are to define the stage of development of H. hippocampus after they are expelled from the male brood pouch and to establish direct or indirect development through an osteological analysis. The ossification process was studied in 120 individuals, from their release to 30 days after birth. To analyse the osteological development, Alcian Blue-Alizarin Red double staining technique for bone and cartilage was adapted to this species. At birth, H. hippocampus presents a mainly cartilaginous structure that ossifies in approximately 1 month. The bony armour composed of bony rings and plates develops in 10 days. The caudal fin, a structure absent in juveniles and adult seahorses, is present at birth and progressively disappears with age. The absence of adult osteological structure in newborns, like coronet, bony rings and plates, head spines and components allowing tail prehensile abilities, suggests a metamorphosis before the juvenile stage. During the indirect development, the metamorphic stage started inside brood pouch and followed outside and leads up to reconsider the status of H. hippocampus newborns."
  • Standardised classification of pre-release development in male-brooding pipefish, seahorses, and seadragons (Family Syngnathidae)[1] "We propose a standardised classification of early syngnathid development that extends from the activation of the egg to the release of newborn. The classification consists of four developmental periods - early embryogenesis, eye development, snout formation, and juvenile - which are further divided into 11 stages. Stages are characterised by morphological traits that are easily visible in live and preserved specimens using incident-light microscopy."

Standardised classification of pre-release development in male-brooding pipefish, seahorses, and seadragons (Family Syngnathidae)

BMC Dev Biol. 2012 Dec 29;12:39. doi: 10.1186/1471-213X-12-39.

Sommer S, Whittington CM, Wilson AB. Source Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse 190, Zürich, CH-8057, Switzerland. stefan.sommer@ieu.uzh.ch.

Abstract

BACKGROUND: Members of the family Syngnathidae share a unique reproductive mode termed male pregnancy. Males carry eggs in specialised brooding structures for several weeks and release free-swimming offspring. Here we describe a systematic investigation of pre-release development in syngnathid fishes, reviewing available data for 17 species distributed across the family. This work is complemented by in-depth examinations of the straight-nosed pipefish Nerophis ophidion, the black-striped pipefish Syngnathus abaster, and the potbellied seahorse Hippocampus abdominalis.

RESULTS: We propose a standardised classification of early syngnathid development that extends from the activation of the egg to the release of newborn. The classification consists of four developmental periods - early embryogenesis, eye development, snout formation, and juvenile - which are further divided into 11 stages. Stages are characterised by morphological traits that are easily visible in live and preserved specimens using incident-light microscopy.

CONCLUSIONS: Our classification is derived from examinations of species representing the full range of brooding-structure complexity found in the Syngnathidae, including tail-brooding as well as trunk-brooding species, which represent independent evolutionary lineages. We chose conspicuous common traits as diagnostic features of stages to allow for rapid and consistent staging of embryos and larvae across the entire family. In view of the growing interest in the biology of the Syngnathidae, we believe that the classification proposed here will prove useful for a wide range of studies on the unique reproductive biology of these male-brooding fish.


Common Name - Seahorse

Country Species
Cuba Hippocampus erectus
Malaysia Hippocampus erectus
Malaysia Hippocampus histrix
Malaysia Hippocampus kuda
Malaysia Hippocampus spinosissimus
Malaysia Hippocampus barbouri
Malaysia Hippocampus comes
Azores Islands Hippocampus histrix
Puerto Rico Hippocampus reidi
St Helena Hippocampus erectus
United Kingdom Hippocampus guttulatus

Table data from Fishbase.[4]

Developmental Stages

Then following images and staging information is from a study of N. ophidion, S. abaster, and H. abdominalis. development.[1]

Syngnathidae development 01.jpg

Figure 1 Early embryogenesis Descriptions of the four stages of the early-embryogenesis period, along with examples for each stage. (A) Animal-pole view of a zygote of N. ophidion ca. 45 min after mating. (B) Animal-pole view of a N. ophidion blastula during early cleavages. (C) Embryonic-shield stage in N. ophidion; the white circle represents the germ ring. (D) Primitive-streak embryo of S. abaster (dechorionated). Scale bars are 0.5 mm.


Syngnathidae development 02.jpg

Figure 2 Eye development Descriptions and schematic drawings of stage-defining eye-structures of the three stages of the eye-development period, along with examples for each stage. (A) Optic-vesicle stage in N. ophidion. (B) Optic-cup stage in S. abaster. (C) Eye-pigmentation stage in N. ophidion. All embryos were dechorionated prior to photographing. Scale bars are 0.5 mm.

Syngnathidae development 03.jpg

Figure 3 Snout formation. Descriptions of the three stages of the snout-formation period, along with examples for each stage. (A) S. abaster embryo (dechorionated) with ventrally developing jaws. (B) H. abdominalis larva with jaws rising frontally. (C) S. abaster larva with an elongated snout. Scale bars are 1 mm.

Syngnathidae development 04.jpg

Figure 4 Newborns of three syngnathid species. The newborn stage represents the first stage of the juvenile period and, for the purpose of this classification, refers to the first day post-release. Shown are (A) N. ophidion, (B) S. abaster, and (C) H. abdominalis. Scale bars are 2 mm.


References

  1. 1.0 1.1 1.2 Sommer S, Whittington CM & Wilson AB. (2012). Standardised classification of pre-release development in male-brooding pipefish, seahorses, and seadragons (Family Syngnathidae). BMC Dev. Biol. , 12, 39. PMID: 23273265 DOI.
  2. Novelli B, Otero Ferrer F, Socorro JA & Molina Domínguez L. (2018). Early development of the longsnout seahorse Hippocampus reidi (Syngnathidae) within the male brood pouch. J. Fish Biol. , 92, 1975-1984. PMID: 29660108 DOI.
  3. Novelli B, Otero-Ferrer F, Socorro JA, Caballero MJ, Segade-Botella A & Molina Domínguez L. (2017). Development of short-snouted seahorse (Hippocampus hippocampus, L. 1758): osteological and morphological aspects. Fish Physiol. Biochem. , 43, 833-848. PMID: 28124205 DOI.
  4. Froese, R. and D. Pauly. Editors. 2012. FishBase. World Wide Web electronic publication. www.fishbase.org, version (12/2012).

Reviews

Articles

Stölting KN & Wilson AB. (2007). Male pregnancy in seahorses and pipefish: beyond the mammalian model. Bioessays , 29, 884-96. PMID: 17691105 DOI.

Wilson AB, Vincent A, Ahnesjö I & Meyer A. (2001). Male pregnancy in seahorses and pipefishes (family Syngnathidae): rapid diversification of paternal brood pouch morphology inferred from a molecular phylogeny. J. Hered. , 92, 159-66. PMID: 11396574

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Cite this page: Hill, M.A. (2019, May 24) Embryology Seahorse Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Seahorse_Development

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