論文

東海大学紀要海洋学部「海─自然と文化」第14巻第２号 1-6頁（2016）
Journal of The School of Marine Science and Technology, Tokai University, Vol.14, No.2, pp.1-6, 2016

タツノオトシゴ属サンゴタツの親の体サイズが子に与える影響
大谷明範＊１・大塚

悠＊２・鈴木宏易＊３・赤川泉＊４The effects of parent body size on young of the Japanese seahorse Hippocampus mohnikei
Akinori Otani, Yu Otsuka, Hiroyasu Suzuki, and Izumi Akagawa

Abstract
The effects of parent size on the number and size of young, and the relationships between reproductive intervals andwater temperature, and between number and size of young, were investigated in the pair rearing Japanese seahorse
Hippocampus mohnikei. Significant sex-related size dif ferences and sex ratio bias were not found in collected fish,
reproduction occurring in any size combination with a 5 mm difference in standard length (mate choice not permitted).
Brood young numbers (18-128) were significantly correlated to female SL, but not to male SL or water temperature. Young
SL was not significantly related to male SL but tended to be related to female SL. Reproductive intervals (11-20 days) were
negatively correlated to water temperature. The relationship between SL and number of young was not significant evenamong broods of the same pair. Consequently, not only do female H. mohnikei not manipulate batch egg number according tomale body size, but also males do not appear to raise larger young from lower initial egg batch sizes.

reproductive cost and exercises the greater mate choice?

Introduction

Males usually cannot acquire more eggs than their capacity
to accommodate and females normally would not spawn

Syngnathid males, including those of Hippocampus, arewith males having a reduced brooding capacity compared toknown to guard eggs in a brood pouch or on the abdominal

female egg production capacity, or may control the egg

region until bir th, an act exclusive to males. In somenumber according to male capacity if only smaller males are

species, males also provide oxygen and nutrition, in addition

available. However, small H. abdominalis males have been

to aiding osmoregulation for eggs in the brood pouch

shown to carr y exceptionally large broods (Mattel and(Berglund et al. 1986, Carcupino et al. 2002, Ripley andWilson, 2009), which raises a further question: is the growthForan 2006, 2009; Stolting and Wilson 2007), the maleof young impaired or not when larger numbers of eggs are

metabolic rate increasing significantly during this time

carried by small males?

(Berglund et al. 1986). In H. zosterae, male metabolic rates

H. mohnikei is a small seahorse inhabiting seagrass beds

increase from 10 to 52% over pregravid levels (Masonjones

in Japan. Although dif ficult to obser ve in the field, its

2001). The question remains, however, which of syngnathid

reproductive behavior can be readily observed in aquaria.

incubating males or egg-producing females has the greater

Yoshino et al. (2009) noted that courtship of aquarium-held

2016年６月24日受付 2017年２月10日受理＊１ マリンピア松島水族館（現，仙台うみの杜水族館）（Marinepia Matsushima Aquarium（Present: Sendai Umino-Mori Aquarium））＊２ 東海大学海洋学部（現，株式会社ビーボックスアクアリウム）（Graduate School of Marine Science and Technology, Tokai University（Present:
B-Box aquarium））＊３ 東海大学海洋科学博物館（Marine Science Museum, Social Educator Center, Tokai University）＊４ 東海大学海洋学部海洋生物学科（Department of Marine Biology, School of Marine Science and Technology, Tokai University）

第14巻第２号（2016）1

大谷明範・大塚H. mohnikei was initiated by either sex. Although males

悠・鈴木宏易・赤川Table 1courted females actively, regardless of the body size of thelatter, females did not court males smaller than themselves.

泉

Female and male Hippocampus mohnikei standard
length (SL) and reproduction frequency in each pair ofthree size classes.

They also suggested that female mate choice was more

SL (mm)definitive than that of males because the probability of

Reproduction (n ＝13)

Female

Male

F＝M

45

45

0

F＞M

50

45

1

F＜M
Medium

45

50

1

F＝M

55

55

0

F＞M

60

55

2

F＜M
Large

55

60

2

body size in various size combinations of male and female
pair rearing, female control of egg number based on male

F＝M

65

65

5

body size or male condition is less likely to take place. On

F＞M

70

65

1

F＜M

65

78

1

spawning was greater when the females actively courted
males, rather than the converse.
Masonjones (1997) demonstrated a positive correlation
between male size and brood size in H. zosterae males
collected from the field, while Vincent and Giles (2003)
showed that female size was the key determinant of thenumber of young released by male H. whitei. Essentially, if
the number of young is positively correlated with female

the other hand, if the number of young is related to maleSmallbody size, either the female might spawn only the numberof eggs appropriate to the male capacity, or the male mightof fspring numbers and body sizes being recorded after

incubate only the number of eggs according to his capacity

fixation in 5% seawater formalin on the bir th day. The

among the eggs received (Vincent 1990; Ahnesjö 1992a,

experiment was performed in the laboratory at Marinepia

1992b).

Matsushima Aquarium, Miyagi Prefecture, Japan, using

In the present study, pair-rearing of dif ferent sizenine female (45-65mmSL) and male (45-78mmSL) pairs,

combinations of male and female pairs of H. mohnikei, washoused in nine glass aquaria (45×30×30 cm in height) withcarried out to investigate the relationship between parent

airlifted filtered water systems. Water temperatures weresize and the numbers or size of offspring, and to explore theallowed to fluctuate under natural conditions, varying frompossibility of female control of egg number or male control

18.7 to 28.1 ℃ during the experiment. Water temperatureof young number or growth.

was recorded at 11 am daily. Seawater was controlled at 30±1 psu and the laboratory maintained in a 12L12D light/

Materials and methods

dark cycle. Equal weights of Artemia larvae were supplied
twice daily to each aquarium.

Fish were collected from a boat utilizing a long hand net

Small, medium and large size class pairs of seahorse wereor by a traditional fisher y technique (Boda-r yo - a trap

established (Table 1), with three replicates of each size

fishery for shrimps and small fishes utilizing a bunch of treeclass: same size female and male (F＝M), female SL 5 mm

branches or bundle of nets sunk in shallow, calm inlet

larger than male (F＞M) and male SL 5 mm larger thanwater), monthly from April to July, 2007 in Matsushima Bay,

female (F＜M) (maximum male size 78 mm SL.)

Miyagi Prefecture, Japan. A total of 64 adult specimens (30Pearson’s correlation coefficient r was calculated between

females and 34 males) were collected, there being no

the number of young and female or male SL, meansignificant sexual ratio bias. Standard lengths weretemperature and male birth interval, mean temperature andmeasured in the laboratory to the nearest 1 mm, following

number of young, and the relationship between the number

Lourie (1999). No significant size difference was apparent

and size of young. p＜0.05 was defined as significant and p

between females (mean±SD＝61.4±6.5 mmSL) and males＜0.1 as showing tendency.

(62.4±9.1 mmSL) (t-test, p＞0.05), pairs being established
for the rearing experiments on the basis of female and male

Results

SL.
Pair-r earing experiments, involving various size

Reproduction occurred 13 times, involving seven of the

combinations of female and male fish, were conducted fromnine pairs (Table 1), the exceptions being the small andJuly to November 2007, reproductive frequencies, bir th

medium size pairs of equal-sized fish (Ssize, F＝M ; Msize,

dates and inter vals between bir ths from the male, and

F＝M). The most frequent occurrence (5 times) was in the2

東海大学紀要海洋学部「海─自然と文化」

タツノオトシゴ属サンゴタツの親の体サイズが子に与える影響

Fig. 1 Relationship between mean temperatures during birthintervals and birth interval length (A), and brood size of
Hippocampus mohnikei (B). Different symbols indicate
different pairs.

Fig. 2 Relationship between standard lengths (SL) of young
and female (A), and male (B) Hippocampus mohnikei.
Numerals on bars indicate number of total young of thefemale or the male and numerals in parentheses indicate
the brood number and without parentheses indicate only
one brood.

l a r g e s t s a m e s i z e d p a i r ( L s i z e , F ＝M ) , a l t h o u g hreproduction took place in all of the female-male size

SL (y＝2.147×−82.37, r＝0.82, n＝7, p＜0.05) (Fig. 3-A),

relationship groups, F＝M (one of three pairs, five times in

but not with male SL (r＝0.58, n＝7, p＞0.05) (Fig. 3-B).

total), F＞M (three of three pairs, four times in total) and F＜M (three of three pairs, four times in total).

The mean size of young per brood bore no correlation
with brood size in any pair, even for that (Lsize, F＝M)

Male birth intervals varied between 11-20 days (Fig. 1),

which reproduced five times (Fig. 4). In fact, the smallest

being about 16 days in a mean water temperature of ca. 23

young of this pair were produced in the second lowest brood℃. The mean water temperature during male birth intervals

size.

had a significant negative correlation with birth inter val
days (y＝−1.799×＋56.87, r＝0.96, n＝6, p＜0.01) (Fig.

Discussion

1-A), but showed no cor relation between male bir thintervals and number of young (n＝6, p＞0.05) (Fig 1-B).

Sexual size dimorphism has not been obser ved in

The mean SL of all young on the birth day was 8.9±0.6

Hippocampus mohnikei from Matsushima Bay at any timemmSL (n＝13 broods), the largest mean SL of the 13 broods(unpublished data), suggesting similar evolutionar ybeing 9.5 mmSL (n＝26 young; parent, Lsize, F＝M) andpressure for body size in both males and females. In thethe smallest, 7.8 mmSL (n＝90 young; parent, Lsize, F＞M).

present study, females reproduced four times with larger

The mean SL of young was significantly related to neither

males, four times with smaller males, and five times with afemale nor male SL, but as female SL increased, the SL ofsimilarly sized male (same pair- no alternative mate choice).

young showed a tendency to decrease (r＝−0.67, n＝7, p＜

The probability of reproductive success did not dif fer0.1) (Fig. 2).

significantly between larger female pairs and larger male

Numbers of young per brood varied between 18 (Ssize, F

pairs, in cases of pair size differences of ca. 5 mm SL and no＞M) and 128 (Lsize, F＝M, one of five broods), the meanmate choice, although Yoshino et al. (2009) reported that

number of young being significantly correlated with female

male larger pairs reproduced more than female larger pairs
第14巻第２号（2016）3

大谷明範・大塚悠・鈴木宏易・赤川泉

n = 13 broods

Fig. 4 Number and SL of young for seven pairs of Hippocampus
mohnikei. Different symbols indicate different pairs.

Also considering that species, a subsequent rearing
experiment demonstrated that the egg size, egg number
and young size are positively related to female body size
(Mattle and Wilson 2009). If H. mohnikei undergoes size
assortative mating in the field, the number of young may be
indirectly related to paternal SL due to competition and/or
mate choice. As survivorship of larger young is generally
Fig. 3 Relationship between number of young and SL of
females (A) and males (B). Numbers of young or means
with SE are shown for individuals.

expected to be better, the r eason for the negative
relationship found here between female SL and young SL in
H. mohnikei requires fur ther clarification. The larger
females might take precedence of the number before thesize of young because smaller young here can have morewhen mate choice was permitted in this species.

chance to survive. The investigation of embryo survivorship

Higher water temperature shortens male birth intervals

in Syngnathus typhle (Mobley et al. 2011) demonstrated thatin Syngnathus typhle and other Syngnathids (Vincent et al.

the eggs of larger females in larger numbers are more1994) as well as other fishes like damselfishes (e.g. Tanaka

viable than those of smaller females in larger numbers,

1998) , although the number of young in one brood does notwhereas the eggs of smaller females in smaller numbers are

increase with temperature (Fig. 1-A, B). Actually subsequent

more viable than those of larger females in smaller

matings occur earlier and successful reproduction morenumbers, a more complex situation than previously thought.

frequently in higher water temperatures.

The present study found no evidence of females actively

The body size of young Hippocampus mohnikei was notcontrolling egg number according to coexisted male bodysignificantly related to either male or female body size (Fig.

size. Similarly, there was no indication that males reduce the2), although a negative tendency (p＜0.1) was foundnumber of eggs accor ding to their own body size.

regarding female SL, larger females having smaller young.

Hatchlings were not always larger in smaller broods, evenOn the other hand, the number of young being significantly

from the same parents (Fig. 4), although in S. typhle,

related to female SL (Fig. 3) is consistent with the findings

Ahnesjo (1992a, b) found a negative correlation between theof several other syngnathid studies (Berglund et al. 1986,

body weight and number of young, with fewer hatchlings

1988, 1989; Vincent 1990, Ahnesjo 1996; Teixeira andresulting in superior body weights. Furthermore, Dzyuba etMusick 2001, Vincent and Giles 2003). However, in H.

al. (2006) suggested that in H. kuda, when relatively few

abdominalis the number of young from pregnant males

embr yos are present, they may attach to functionallycollected in the field (without information on maternal fish)

advantageous sites. However, the present findings suggest

had a significant positive relationship with male SL (Woods

the possibility that not only male body size and brood2005). Furthermore, Woods (2005) showed that the SL of

number but also other factors, including male condition,

young was related to neither male SL nor young number.

may affect hatchling size.

4

東海大学紀要海洋学部「海─自然と文化」

タツノオトシゴ属サンゴタツの親の体サイズが子に与える影響

Masonjones, H.D. (2001): The effect of social context andAcknowledgements

reproductive status on the metabolic rates of dwar f
seahorses (Hippocampus zosterae ). Comparative

We greatly appreciate the supports of Mr. T. Kawamura

Biochemistr y and physiology – Part A: Molecular andand Mr. K. Sawaki (Marinepia Matsushima Aquarium), and
Mr. Tsunoda (Master of Boda-ryo in Matsushima) for their
help in sampling and encouragement for our research. Our
sincere thanks go to Dr. G. Hardy (Ngungur u, New
Zealand) for his comments on the manuscript and help withEnglish.

Integrative physiology, 129, 541-555.
Mattel, B., A.B. Wilson (2009): Body size preferences in the
pot-bellied seahorse Hippocampus abdominalis: choosy
males and indiscriminate females. Behav. Ecol. Sociobiol.
63, 1403-1410.
Mobley, K.B., C. Kvarnemo, I .Ahnesjo, C. Par tridge, A.
Berglund and A.G. Jones (2011): The effect of maternal
body size on embr yo sur vivorship in the broods ofReferences
Ahnesjö, I. (1992a): Consequences of male brood care: weightand number of newborn in a sex-role reversed pipefish.
Functional Ecol. 6, 274-281.
Ahnesjö, I. (1992b): Fewer newbor n result in superior
juveniles in the paternally brooding pipefish Syngnathus
typhle L. J. Fish Biol. 41, 53-63.
Ahnesjö, I. (1996): Apparent resource competition amongembr yos in the brood puch of a male pipefish. Behav.
Ecol. Sciobiol. 38, 167-172.
Berglund, A., G. Rosenqvist and I. Svensson (1986): Reversed
sex roles and parental energy investment in zygotes of
two pipefish (Syngnathidae). Mar. Ecol. Prog. Ser. 29,
209-215.
Berglund, A., G. Rosenquvist and I. Svensson (1988): Multiple
matings and pater nal brood care in the pipefish,
Syngnathus typhle. Oikos 51, 184-188.
Berglund, A., G. Rosenqvist and I. Svensson (1989):
Reproductive success of females limited by males in two
pipefish species. Am. Nat. 133, 506-516.
Carcupino, M., A. Baldacci, M. Mazzini and P. Franzoi (2002):
Functional significance of the male brood pouch in the
reproductive strategies of pipefishes and seahorses: amorphological and ultrastructural comparative study on
three anatomically different pouches. J. Fish Biol. 61,
1465-1480.
Dzyuba, B., K.J.W. Van Look, A. Cliffe, H.J. Koldewey and W.V.
Holt (2006): Effect opf parental age and associated size on
fecundity, growth and sur vival in the yellow seahorse
Hippocampus kuda. J. Experim. Biol. 209, 3055-3061.
Lourie, S.A. (1999): Seahorse measurement protocol. 158-161.
In, Lourie, S.A., A.C.J .Vincent and H.J. Hall eds.,
Seahorses: an identification guide to the world’s species
and their conservation. Project Seahorse, London.
Masonjones, H.D. (1997): Sexual selection in the dwar f
seahorse, Hippocampus zosterae (Syngnathidae): an
investigation into the mechanisms determining thedegree of male vs. female intrasexual competition andintersexual choice. PhD Thesis. T ufts University,
Massachusetts.

第14巻第２号（2016）

pregnant male pipefish. Behav. Ecol. Sociobiol. 65, 11691177.
Ripley, J.L. and C.M. Foran (2006): Dif ferential parental
nutrient allocation in two congeneric pipefish species(Syngnathidae: Syngnathus spp.). J. Exp. Biol. 209, 11121121.
Ripley, J.L. and C.M. Foran (2009): Direct evidence forembryonic uptake of paternally-derived nutrients in two
pipefishes (Syngnathidae: Syngnathus spp.). J. Comp.
Physiol. B179, 325-333.
Stolting, K.N. and A.B. Wilson (2007): Male pregnancy inseahorses and pipefish: beyond the mammalian model.
BioEssays 29, 884-896.
Tanaka, Y. (1998): Reproductive behavior and morphology ofeggs and larvae of damselfish. J. School Mar. Sci. & Tech.
Tokai Univ. 45, 167-179. (in Japanese and with English
abstract and figure captions).
Teixeira, R.L. and A. Musick (2001): Reproduction and food
habits of the lined seahorse, Hippocampus erectus(Teleostei: Syngnathidae) of Chesapeake Bay, Virginia.
Brazilian J. Biol. 61, 79-90.
Vincent, A.C.J. (1990): Reproductive ecology of seahorses.
PhD Thesis, Cambridge University, U.K.
Vincent, A.C.J., I. Ahnesjo and A. Berglund (1994): Operationalsex ratio and behavioural sex differences in a pipefish
population. Behav. Socio. Biol. 34(6), 435-442.
V incent, A.C.J. and B.G.Giles (2003): Cor r elates ofreproductive success in a wild population of Hippocampus
whitei. J. Fish Biol. 63(2), 344-355.
Vincent, A.C.J. and L.M. Sadler (1995): Faithful pair bonds inwild seahorses, Hippocampus whitei. Anim. Behav. 50,
1557-1569.
Woods, C.M.C. (2005): Reproductive output in the maleseahorses, Hippocampus abdominalis, from Wellington
harbour, New Zealand: Implications for conser vation.
New Zealand J. Mar. Fresh. R. 39, 881-888.
Yoshino, M., K. Araki, H. Suzuki and I. Akagawa (2009):
Courtship behavior, mate choice and potential mating
system variations in Hippocamps mohnikei. Bull. Inst. Res.
& Develop. Tokai Univ. 30, 21-29 (in Japanese and withEnglish abstract and figure captions).

5

大谷明範・大塚悠・鈴木宏易・赤川

要

泉旨

ペア飼育下のタツノオトシゴ属サンゴタツにおいて，親の体サイズが子の数と体サイズに与える影響，水温と繁殖間隔の関係，および子の数とその体サイズの関係を調査した．採集したサンゴタツには，性的なサイズの相違や性比の偏りは見られなかった．配偶者選択のできないペア飼育下では，雌雄のどちらが標準体長で５mm 大きくても，同じ体長でも繁殖が行われた．繁殖間隔（11-20日）は水温と負の相関を呈したが，子の数とは相関しなかった．子の体長はオスの体長には相関しなかったが，メスの体長には相関する傾向がみられた（P＜0.1）．一回の産仔数（18-128）はメスの体長に有意に相関したが，オスの体長や水温には相関しなかった．子の数と子の体サイズの関係は，同じペアからの場合ですら有意ではなかった．以上の結果からすると，メスのサンゴタツは配偶相手のオスの体サイズによって産卵数を調整している
わけではなく，いっぽうオスは受け取った卵数が少ないほど大きく育てて産出するということもなさそうであった．

6

東海大学紀要海洋学部「海─自然と文化」