A new gelatinous host for pelagic fishes: First in situ record
of an association between driftfishes (Stromateiformes,
Ariommatidae) and nudibranchs (Mollusca, Phylliroidae)
Murilo N. L. Pastana
| G. David Johnson
| Bruce Mundy
| Alessio Datovo
Museu de Zoologia da Universidade de S˜ao Paulo, S˜ao Paulo, Brazil
Department of Vertebrate Zoology-Division of Fishes, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, USA
Ocean Research Explorations, Honolulu, Hawai'i, USA
Bishop Museum, Honolulu, Hawai'i, USA
Murilo N. L. Pastana, Museu de Zoologia da
Universidade de S˜ao Paulo, S˜ao Paulo, SP,
Herbert R. and Evelyn Axelrod Endowment
Fund for Systematic Ichthyology; Sara E. and
Bruce B. Collette Postdoctoral Fellowship in
Systematic Ichthyology; Smithsonian Senior
We describe the first recorded association between fishes and nudibranchs in
epipelagic waters. In situ observations and photographs of a juvenile spotted driftfish
Ariomma regulus (Stromateiformes; Ariommatidae) swimming alongside the planktonic
nudibranch Phylliroe lichtensteinii (Gastropoda; Phylliroidae) were made during black-
water scuba dives off Palm Beach, Florida, United States of America. In this paper, we
describe this behavior, highlighting a previously undocumented zooplanktonic host
used by fishes. This finding also demonstrates the importance of community science
in advancing our understanding of the early life history of marine species.
blackwater photography, citizen science, medusafishes, symbiosis, Western Atlantic
Over the past 50 years, a number of studies have documented the
complex interactions between juvenile fishes and pelagic gelatinous
organisms, including jellyfishes, comb-jellies, radiolarians, nudibranchs,
nemerteans, and tunicates. These pelagic gelatinous organisms are
often referred to as gelata (Haddock, 2004) despite not being a natural
group. In these interactions, juvenile fishes use gelata as shelter or ref-
uge in pelagic environments that are usually devoid of physical com-
plexity (Griffin et al., 2019; Lynam & Brierley, 2006; Mansueti, 1963).
Fishes may also associate with gelata to feed on prey captured by
these organisms, eat parasites off the gelata, or even feed on the gelata
itself (Harbison, 1993; Janssen & Harbison, 1981; Mansueti, 1963;
Pastana et al., 2022;Riascoset al., 2012).
Twenty-one families of teleost fishes are known to associate with
gelata: Amarsipidae, Ariommatidae, Balistidae, Bathylagidae, Bramidae,
Bythitidae, Carangidae, Caristiidae, Centrolophidae, Emmelichthyidae,
Ephippidae, Gadidae, Girellidae, Icosteidae, Myctophidae, Nomeidae,
Sparidae, Stromateidae, Syngnathidae, Tetragonuridae, and Zaproridae
(Arai, 1988; Auster et al., 1992; Drazen & Robison, 2004;
Harbison, 1993; Horn, 1970; Janssen & Harbison, 1981;
Kingsford, 1993; Lynam & Brierley, 2006; Mansueti, 1963; Nonaka
et al., 2021; Ohtsuka et al., 2009; Pastana et al., 2022; Purcel &
Arai, 2001). Of these, amarsipids, centrolophids, ariommatids, nomeids,
tetragonurids, and stromateids are grouped in the order Stromatei-
formes (sensu Pastana et al., 2021), and together they represent the
fish lineage with the most abundant record of association with gelata.
The order comprises 77 extant species distributed in 16 genera
(Haedrich, 1967; Pastana et al., 2021; Van der Laan & Fricke, 2023),
which are found in temperate and tropical marine waters, in both oce-
anic and coastal environments, and in various depths between the sur-
face and 800 m (McDowall, 2001). Though most stromateoids are
pelagic, ariommatids are deep-water demersals. Adult ariommatids are
found in deep waters over the shelves and slopes of continents,
islands, and submerged banks in the Atlantic, Indian, and Pacific oceans
(Horn, 1972), eastward to the Nazca and Sala-y-Gomez ridges
Received: 23 June 2023 Revised: 26 July 2023 Accepted: 31 July 2023
J Fish Biol. 2023;1–5. wileyonlinelibrary.com/journal/jfb © 2023 Fisheries Society of the British Isles. 1
(Parin, 1991), but not in the continental areas of the eastern Pacific. In
both the Eastern and Western Atlantic, adult ariommatids are usually
found in schools inhabiting offshore waters over muddy bottoms
(Horn, 1972). Larvae and small juveniles, on the contrary, occur in the
surface layers (Lamkin, 1997).
All six extant stromateiform families display some kind of associa-
tion with gelata, earning them the common name of medusafishes. A
recent phylogenetic study indicates that such behavior is plesio-
morphic within the order (Pastana et al., 2021). Although interactions
between stromateiforms and gelata are often recorded in the
literature (e.g., Harbison, 1993; Janssen & Harbison, 1981;
Mansueti, 1963), records of ariommatids associating with zooplank-
tonic invertebrates are rare. As of 2023, there is a single published
record describing the association between ariommatids and gelata
(Fowler, 1934). Here we describe the first in situ observation of the
association between a juvenile ariommatid and a gelata, and the first
record of a fish using nudibranchs as hosts in open pelagic waters.
This report provides not only important information on the life history
of medusafishes but also expands the number of hosts used by fishes
while displaying this unusual associative behavior with pelagic marine
The described observation occurred during night epipelagic
(blackwater) drift dives conducted by Linda Ianniello. Photo
documentation was made using a Nikon D500 camera with a
60 mm lens, a Nauticam underwater housing, and three Inon
strobes. Photographs in Figure 1weretakeninPalmBeach,Florida,
United States of America (2643007.100 N, 7958034.900 W). The
fish and nudibranch (Figure 1a–c) were observed on February
10, 2022, circa 20:38 local time (GMT-4), at an approximate depth
of 12 m and were followed down to a depth of 21 m. The photo-
graphs were taken at an approximate distance of 18 cm between
the camera and organisms. The average depth of the dive location
was 63 m. The average water temperature was 24C. The solitary
juvenile fish (Figure 1d) was photographed on April 17, 2022, circa
20:44 local time (GMT-4) at an approximate depth of 18 m. The
average water temperature was 25.5C. This study is based solely
on in situ observations of fishes during night epipelagic dives–
animal capture and experimentation were not performed, and the
research did not inflict harm to the fishes. No permits were required
to conduct this study.
Using the photographs and locality information, we compared the
fish images to the color patterns, dorsal-fin morphology, and dorsal-
and anal-fin ray counts listed in previous studies (i.e., Ahlstrom
et al., 1976; Haedrich, 1967; Lamkin, 2005; McKenney, 1961; Pastana
et al., 2021) and observed in museum specimens to identify the indi-
vidual. Counts were made by hand and aided by the count tool
FIGURE 1 The ariommatid Ariomma
regulus in open pelagic waters. (a–c)
Juvenile fish in association with the
nudibranch Phylliroe lichtensteinii,
February 10, 2022; (d) Juvenile fish in
right lateral view, April 22, 2022. All
photos by Linda Ianniello.
2PASTANA ET AL.
available in Adobe Photoshop. A list of comparative materials used in
this study can be found in the Material Examined section, with institu-
tional acronyms following Sabaj (2020). The photographed fish is the
spotted driftfish, Ariomma regulus (Stromateiformes, Ariommatidae)
(Lamkin, 2005; McKenney, 1961).
Fish meristic and morphometric data taken from the photographs
are as follows: body compressed, snout bluntly rounded, eyes large.
Greatest body depth at dorsal-fin origin. Dorsal fin XI, 15, origin at
approximately first third of body. Base of first dorsal-fin spine inserted
slightly anterior to vertical through origin of pelvic fin, base of first
dorsal-fin soft ray slightly anterior to vertical through origin of anal
fin. Dorsal fin notched almost to base in front of soft-rayed portion.
Anal-fin III, 15. Pelvic- fin I, 5, tips of branched rays longer than pelvic-
fin margin and free from interradial membrane. Caudal-fin forked. Live
colouration of A. regulus described based on Figure 1d, composed of a
conspicuous barred pattern. Ground colouration light gray, slightly
darker dorsally. Eyes brown, pupils black. Upper and lower jaws,
snout, and chin area lacking pigmentation. Posterior portion of the
head with dark-brown pigmentation with irregular margins starting at
the occipital region and extending ventrally through the posterior
margin of the orbital rim onto the preopercular area. Body pigmenta-
tion comprises five dark-brown bars of similar width and irregular
The photographed juvenile fish can be identified as an ariomma-
tid based on a notched dorsal fin, 11 unbranched and 15 branched
dorsal-fin rays, 3 unbranched and 15 branched anal-fin rays, and a
body colouration consisting of vertical bars. Ariommatids are the
only medusafishes that have a combination of deeply notched
(i.e., externally separated) anterior and posterior dorsal fins, 25–28
dorsal-fin rays, and 15–19 anal-fin rays (Haedrich, 1967;Haedrich&
Horn, 1972;Pastanaet al., 2021). Currently, the family includes eight
species in the genus Ariomma.ThreeAriomma species are currently
known for the Western Atlantic: Ariomma regulus,Ariomma bondi,
and Ariomma melanum. We identified the photographed specimen as
A. regulus based on the fin shape and pigmentation pattern described
and illustrated for this species (Lamkin, 2005; McKenney, 1961).
Juveniles of this species have a distinct color pattern consisting of
five vertical dark-brown bars. Moreover, juvenile A. regulus has a
conspicuously inflated top of the head compared to other ariomma-
tids (e.g. a concave frontal region in A. melanum [Lamkin, 1997:
fig. 1]). Based on available descriptions (McKenney, 1961: fig. 3a,b),
we estimate the total length of the photographed specimens in
Figure 1to be 16–24 mm.
The total length of the nudibranch is consequently estimated to
be between 48 and 72 mm. It is unequivocally identified as a member
of Phylliroidae due to its pelagic behavior and aberrant morphology,
with a transparent and laterally compressed body (Lalli &
Gilmer, 1989). The more compressed body, longer tentacles,
extremely reduced foot, and length greater than 25 mm allow its
placement in the genus Phylliroe rather than Cephalopyge (Gershwin
et al., 2018; Lalli & Gilmer, 1989). Phylliroe currently has two valid spe-
cies, Phylliroe lichtensteinii and Phylliroe bucephala (Gershwin
et al., 2018). P. lichtensteinii has been reported to have three ovotestis
lobes, same as found in the photographed specimen (vs. two in
P. bucephala: Gershwin et al., 2018; Ralph, 1959).
Fish-gelata relationships are rare among teleosts, and only 21 fish
families are known to interact with gelata (Mansueti, 1963; Pastana
et al., 2022; Purcel & Arai, 2001). These associations typically involve
scyphozoans, hydrozoans, and cubozoans (Harbison, 1993; Jenkins,
1983; Lawley & Júnior, 2018; Mansueti, 1963; Maul, 1964;Purcel&
Arai, 2001). Beyond cnidarians, medusafishes have been reported in
association with ctenophores (Mansueti, 1963; Matthews &
Shoemaker, 1952; Purcel & Arai, 2001), and tunicates (Harbison, 1993;
Janssen & Harbison, 1981; Pastana et al., 2021). Our paper provides
the first in situ observation of an ariommatid associating with a nudi-
branch in pelagic waters. During the encounter in 2022, the fish and
nudibranch were swimming among the zooplankton, with the fish
actively following the nudibranch. When camera lights shined on the
fish and the nudibranch for extended periods, or when multiple divers
surrounded them, the Ariomma actively oriented itself in a position that
kept its host between the fish and divers (Figure 1a–c). The fish did
not abandon its host even during the closest interaction with the pho-
tographers (18 cm from the lens to the subject). Eventually, the
gastropod swam to deeper waters, followed closely by the fish. The
photographs and in situ observations suggest that A. regulus associates
with P. lichtensteinii, seeking shelter or refuge during its initial life
stages (Figure 1).
Information on the early life history of Ariommatidae is scarce,
limited to their abundance in ichthyoplankton surveys (Lamkin, 2005),
and little is known about the behavior in early pelagic stages. Prior to
our study, the only documented association between ariommatids and
gelata came from a brief comment in Fowler (1934), reporting a
36 mm juvenile Psenes indicus (=Ariomma indica) inside a 305 mm
diameter ctenophore. Interactions between fishes and nudibranchs
were previously known from a parasitic relationship between the
dorid nudibranch Gymnodoris nigricolor and the shrimp goby Amblye-
leotris japonica, where the nudibranch attaches itself to the goby's fins
and feeds off them (Karplus, 2014; Williams & Williams, 1986).
A. regulus–P. lichtensteinii association seems to be limited to a com-
mensal behavior of the juvenile fish, which takes advantage of the
presence of the nudibranch by seeking shelter in open pelagic waters.
No antagonistic behavior was observed between the two species.
Phylliroe also associates with other gelata, with juveniles attaching to
the inner bell of the hydrozoan Zanclea costata and feeding on its ring,
radial canals, and manubrium (Lalli & Gilmer, 1989). Adults are
reported to prey on larvaceans (Oikopleura albicans) and hydrozoans
(Aequorea; Lalli & Gilmer, 1989).
Information on the biology and early life history of many marine
pelagic fishes is still limited—observations on the behavior of juvenile
A. regulus have been virtually unknown prior to this study. In this con-
text, the information gathered by blackwater divers has been critical
to a number of recent publications (e.g., Nonaka et al., 2021; Pastana
et al., 2022). These highlight the importance of community science, as
the images captured by divers provided critical data on the morphol-
ogy of marine fish larvae and their interactions with other planktonic
PASTANA ET AL.3
1.1 |Material examined
Amarsipidae: Amarsipus carlsbergi (SIO 75-122; 50.4 mm SL). Ariom-
matidae: Ariomma indicum (MZUSP 123249; 129.9 mm SL); Ariomma
bondi (MZUSP 86717; 125.3 mm SL). Centrolophidae: Psenopsis anom-
ala (MZUSP 119730; 74.2 mm SL); Psenopsis cyanea (MZUSP 123244;
138.6 mm SL); Centrolophus niger (CSIRO H 2421-01; 245.1 mm SL);
Schedophilus sp. (MCZ 161887; 89.2 mm SL); Seriolella porosa (USNM
176593; 198.8 mm SL); Tubbia tasmanica (CSIRO H 6979-03;
325.2 mm SL); Icichthys lockingtoni (OS 16732; 102.3 mm SL); Hypero-
glyphe perciformis (MZUSP 119733; 150.4 mm SL). Nomeidae: Psenes
cyanophrys (MZUSP 106392; 152.6 mm SL); Psenes sio (MZUSP
123248; 184.3 mm SL); Cubiceps baxteri (=reidentified to Ariomma
melana; MZUSP 123246; 134.9 mm SL); Cubiceps whiteleggii (MZUSP
123247; 107.5 mm SL); Cubiceps pauciradiatus (MZUSP 80701;
88.6 mm SL); Nomeus gronovii (MZUSP 67590; 81.3 mm SL). Stroma-
teidae: Peprilus triacanthus (MZUSP 123240; 128.9 mm SL); Peprilus
paru (MZUSP 67608; 80.9 mm SL); Pampus cinereus (MZUSP 119734;
72.4 mm SL); Stromateus brasiliensis (MZUSP 51279; 136.1 mm SL).
Tetragonuridae: Tetragonurus cuvieri (MZUSP 123241; 94.7 mm SL).
Murilo N. L. Pastana: Data collection, figure preparation, manuscript
writing, manuscript editing, literature review. Alessio Datovo:
Figure preparation, manuscript writing, manuscript editing. Bruce
Mundy: Manuscript editing, literature review. G. David Johnson: Man-
uscript editing, literature review.
We are greatly indebted to Linda Ianniello for her photographs and
contributing with the diving, photographic methods, and behavioral
observations. We thank Tauana Cunha (Smithsonian Tropical Research
Institute) for her help with the identification of the nudibranchs.
Matthew Girard helped the authors with editing of Figure 1. Images
published were first available on the Facebook Blackwater Photo
an online forum that promotes discussions between underwater pho-
tographers and ichthyologists. This work was funded by the Sara
E. and Bruce B. Collette Postdoctoral Fellowship in Systematic
Ichthyology (MNLP), a Smithsonian Senior Postdoctoral Fellowship
(AD), and by the Herbert R. and Evelyn Axelrod Endowment Fund for
Systematic Ichthyology (GDJ). This is Ocean Research Explorations
Murilo N. L. Pastana: Sara E. and Bruce B. Collette Postdoctoral Fel-
lowship in Systematic Ichthyology–Smithsonian Institution. Alessio
Datovo: Smithsonian Senior Postdoctoral Fellowship. G. David John-
son: Herbert R. and Evelyn Axelrod Endowment Fund for Systematic
Murilo N. L. Pastana https://orcid.org/0000-0003-3906-0863
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How to cite this article: Pastana, M. N. L., Johnson, G. D.,
Mundy, B., & Datovo, A. (2023). A new gelatinous host for
pelagic fishes: First in situ record of an association between
driftfishes (Stromateiformes, Ariommatidae) and nudibranchs
(Mollusca, Phylliroidae). Journal of Fish Biology,1–5. https://
PASTANA ET AL.5