Mulloidichthys flavolineatus (Lacepede, 1801)

Uiblein, Franz, Gouws, Gavin, Johnson, Jeffrey W., Lobel, Phillip S. & Shaheen, Shaker, 2020, Junior synonymy of Mulloides armatus and intraspecific comparisons of the yellowstripe goatfish Mulloidichthys flavolineatus (Mullidae) using a comprehensive alpha-taxonomy approach, Cybium 44 (2), pp. 137-155 : 146-151

Mulloidichthys flavolineatus intraspecific comparisons

Size groups

Subspecies and populations

In adult specimens, considerable overlap occurs among subspecies and populations in morphometric and meristic characters ( Tabs I , II, IV; Fig. 3 ). In morphometric characters, size-related allometric variation, i.e. between juveniles and adults (see above), is often much larger than body-shape variation among subspecies and populations (Tabs I-III; Fig. 3 ).

Mulloidichthys f. flavolineatus and M. f. flavicaudus show considerable overlap in all morphometric and several meristic characters when compared directly. Slight differences exist in the number of lateral-line scales (34- 38 in M. f. flavolineatus vs. 33-35 in M. f. flavicaudus ; Tabs II-IV) and in a lower first dorsal-fin spine detectability in adult M. f. flavicaudus (25% vs. 58.6% in M. f. flavolineatus in the Indian Ocean and 76.2% in the Pacific; Tabs II, IV). However, no clear and consistent distinction is reached even when combining number of lateral-line scales and first dorsal-fin spine detectability with any other characters.

The populations of M. f. flavolineatus from the Indian Ocean and Pacific overlap considerably in morphometric and meristic characters (Tabs I-IV; Fig. 4 ). Dorsal-fin spine detectability is slightly higher in the Pacific compared to the Indian Ocean population (76.2 vs. 58.6%), being highest in the Hawaiian Archipelago (90%; Tabs I , II, IV). The most prominent distinction among the four Pacific populations occurs in the three specimens from Wake Atoll, which show longer heads, barbels and pectoral fins, and larger eyes than similar-size specimens of all other M. f. flavolineatus populations and M. f. flavicaudus ( Fig. 4 ). In addition, the Wake specimens differ from the Hawaiian Archipelago population in deeper head through eye, slightly shorter anal-fin base and slightly shallower body and higher anal and first dorsal fins ( Tab. I ; Fig. 4 ). Several specimens of the Hawaiian population show relatively short heads, small eyes and short barbels, as apparent when plotting these characters against SL ( Fig. 4 ).

Caudal-fin colour, indicated to be an important diagnostic character for M. f. flavicaudus in the original description (Fernández-Silva and Randall in Fernández-Silva et al., 2016), is either yellow or whitish-grey in both subspecies. Evidence for the occurrence of whitish-grey caudal fins in M. f. flavicaudus comes from an in situ photograph of a shoal encountered off Dahab, Gulf of Aqaba, northern Red Sea ( Fig. 1C ). Similarly as documented by photographs from Oman and the Maldives published in Fernández-Silva et al. (2016), the northern Red Sea shoal consists of several individuals with either yellow or whitish-grey caudal fins. Further evidence comes from a video footage from off Marsa Alam, Egypt (northern Red Sea), which can be inspected by using the following link: https://www.shutterstock.com/ de/video/clip-10310861-red-sea-goatfish-parupeneusforsskali-feeding-on. An original copy of this footage has been obtained by the first author from the online provider. It shows five M. flavolineatus associated with two Red Sea goatfish Parupeneus forsskali (Fourmanoir & Guézé, 1976) . Only two of the five specimens show a yellowish caudal fin, while the other three show a whitish-grey caudal fin. Though yellow caudal fins appear to occur rather infrequently in M. f. flavolineatus ( Fernández-Silva et al., 2016) , they can be encountered in many areas of the Indo-Pacific and as widely separated as Sodwana Bay, South Africa, WIO (Plate 1D in Uiblein, 2011), the Seychelles, WIO ( Fig. 1D ), the Coral Sea, Queensland, SW Pacific ( Fig. 1B ), and the Wake Atoll, central NW Pacific ( Fig. 3C ).

Among juveniles of the two subspecies and two populations, slight differences in morphometric characters can be found such as a shallower body at anal-fin origin in the Indian Ocean population of M. f. flavolineatus , and longer barbels, shorter caudal peduncle and higher first dorsal fin in M. f. flavicaudus (Tab. III) However, because only a relatively small data set is available for juveniles these results need to be interpreted with caution.

The univariate statistical comparisons among M. f. flavicaudus and the Indian Ocean and Pacific populations of M. f. flavolineatus detected significant differences in 18 of 40 morphometric characters ( Tab. V ). Mulloidichthys f. flavicaudus and M. f. flavolineatus of the Pacific differ from each other in 16, M. f. flavicaudus and M. f. flavolineatus of the Indian Ocean differ in 12, and the two populations of M. f. flavolineatus differ in two morphometric characters ( Tab. V ). Regarding six important meristic characters, M. f. flavicaudus and M. f. flavolineatus of the Pacific differ significantly in five, M. f. flavicaudus and M. f. flavolineatus of the Indian Ocean in three and the two populations of M. f. flavolineatus in a single character (Tab. IV).

The results of PCA based on morphometric characters are shown in Tab. VI and Fig. 5 . No clear distinction among data grouped into subspecies and large-scale populations (Indian Ocean and Pacific) occurs, but statistical differences among these groups can be found for loadings of three of the first four principal components ( Tab. V ). The best separation of M. f. flavicaudus results from combining the second and third principal components, which have highest loadings for body depth (PC2; Tab. VI), and second dorsal- and anal-fin height (PC3; Tab. VI). Still, overlap along these component axes occurs between M. f. flavicaudus and three Indian Ocean and three Pacific specimens ( Fig. 5 ). The Pacific population is statistically separable from the Indian Ocean population based on the fourth component, which has highest loadings for eye size and interdorsal distance (Tab. VI), though considerable overlap occurs ( Fig. 5 ). Along the first principal component, which accumulates 21.9% of total variance explained, the three Wake Atoll specimens separate well from nearly all other conspecifics, the only exception being the smallest adult of the Indian Ocean population ( Fig. 5 ). Head, snout, barbel and pectoral-fin length, and head depth through eye have the highest first component loadings (Tab. VI).

We conclude that the two subspecies can at best be understood as two well-differentiated populations. The Wake Atoll specimens are considerably differentiated from most other conspecifics in body shape, while no evidence for differentiation in meristic characters and colour patterns was found.

Taxonomy

Mulloidichthys flavolineatus (Lacepède, 1801) (Tabs I-IV; Figs 1 , 3 , 4 )

Mullus flavolineatus Lacepède, 1801: 384 , 406; no locality stated. No original types known.

Mulloidichthys flavolineatus : Uiblein, 2011; Fernández-Silva et al., 2015.

Two subspecies: Mulloidichthys f. flavolineatus and M. f. flavicaudus Fernández-Silva & Randall in Fernández-Silva et al., 2016

Material examined

Mulloidichthys flavolineatus flavolineatus (n = 87)

Types (n = 3): BPBM 20135 , NT, 162 mm SL, Indian Ocean, Mauritius, East Coast, Oyster Bay (= Baie aux Huîtres), 19°43’S, 63°21’E, 1.5 m depth ; QM I.122, HT of Mulloides armatus , 118 mm SL, SW Pacific, E Australia, Queensland, most probably Western Coral Sea ( Fig. 1A ) ; MNHN B-2352, ST of Mulloidichthys vanicolensis , 85 mm SL, SW Pacific, Solomon Islands: Vanikoro, Sta. Cruz .

Wake Island, Wake Atoll, Central NW Pacific (n = 3): BPBM 4089, 3, 206-221 mm (largest specimen, Fig. 3A ).

Hawaiian Archipelago (n = 10): Midway Atoll: BPBM 25517, 119 mm SL and BPBM 15308, 152 mm SL; NW Hawaiian Islands: BPBM 4087, 287 mm SL, Laysan Island ; BPBM 4088, 2, 138-226 mm SL, Lisianski Island; Hawaii: Oahu: BPBM 1749, 185 mm SL, Honolulu; BPBM 1750, 172 mm SL, Honolulu; BPBM 25457, 126 mm SL, Waianae coast; BPBM 25674, 174 mm SL, Honolulu; NHMO J 2135, 217 mm SL, no locality information.

Other areas of the Pacific (n = 21): South China Sea, Vietnam: HIFIRE 58228, 149 mm SL, Nha Trang, Hon Tre Island ; Micronesia: Caroline Islands: BPBM 24628 , 2 (of 13), 95-163 mm SL, Puluwat Atoll , lagoon side, 07°20’N, 149°11’E ; Mariana Islands: BPBM 77 , 1 (of 8), 235 mm SL , Guam; Palau: CAS 206563, 111 mm SL, reef flat off Ngajangel Island on east side of atoll, 8°4’47”N, 134°43’52”E ; Japan, Marcos Island : BPBM 7087, 210 mm SL, N end, reef flat, 1 m depth; BPBM 7088, 197 mm SL, reef flat, 1.5 m depth; Polynesia : Samoa: ZMUC 49452 , 95 mm SL, Pago Pago , harbour ; Tonga: ZMUC 49491, 168 mm SL, Nukualofa; Rapa Island: BPBM 12937, 164 mm SL, E side of Akatamiro Bay , 3 m depth ; Kiribati, Phoenix Islands: BPBM 15299 , 3 (of 18), 146-154 mm SL, Hull Island, Orona Atoll; BPBM 25645 , 3 , 72-80 mm SL, Kanton Island ; French Polynesia: ZMUC 49500, 106 mm, Tahiti; ANSP 83811, 3 (of 4), 82-87 mm, Tuamoto Archipelago, Takaroa ; Marquesas Islands: BPBM 2136, 200 mm SL, Nukuhiva .

Indian Ocean, except for NW Indian Ocean and Red Sea (n = 36): Western Indian Ocean : Mozambique : SAIAB 18072 , 3 , 109-116 mm SL, Delagoa Bay , 25°58’40”S, 32°35’20”E ; South Africa: SAIAB 86370, 254 mm SL, KwaZulu-Natal, Ribbon Reef, Sodwana Bay , 27°29.37’S 32°41.38’E, 12-18 m depth ; Seychelles: SAIAB 77080 , 70 mm, Mahé, Baie Ternay, 4°38’47”S, 55°22’43”E ; ANSP 108690 , 3 (of 12), 65-68 mm SL, Aldabra Island near Ile Picard, 9°25’S 46°15’E ; ANSP 114425 , 2 (of 51), 185- 218 mm SL, Amirante Islands, St. Joseph Island, coral bank SW of Resource Island , 5°26’S, 53°22’E, 0-6 m ; Chagos: SAIAB 15361 , 2 , 170-179 mm SL, NW corner of Isle Boddam on ocean side; Mascarenes : Mauritius: MNHN 1994- 0552 , 288 mm SL ; SAIAB 58605 , 7 (of 19), 73-120 mm SL, just South of Pointe Petite , 20°12’S, 57°24’E ; SAIAB 86582 , 3 , 289- 206 mm SL, fish market, La Morne, South-West Mauritius, 20°28.190’S, 57°20.658’E ; Réunion: MNHN 1965-27, 153 mm SL, Reunion , – 21°7’1”S, 55°34’59”E ; Rodrigues: SAIAB 68799 , 5 , 95-132 mm SL, off Port Mathurin , Ile Hollandaise ; SAIAB 70580, 180 mm SL, north of Grand Bay; Eastern Indian Ocean : Indonesia, Sumatra : RMNH 13299 , 3 (of 8), 123-177 mm SL, Sumatra, Sabang Bay , Pulau Weh ; ZMA 132457, 123 mm SL, Sumatra, Aceh, Simaloer Island, Labuan Badjan; W Australia, Cocos-Keeling Islands : ANSP 159138, 269 mm SL, West Island , 1.5-3 km E of N end of island, 12°7’35”S, 96°50’55”E ; ANSP 159142, 228 mm SL, West Island , 1.5-3 km E of north end of island, 12°7’40”S, 96°49’50”E, 6-7.5 m depth.

Figures

Figure 1. – A: HT of Mulloides armatus, QM I.122, 118 mm SL, Queensland, E Australia, western SW Pacific (Jeff Johnson); B: M. flavolineatus flavolineatus, AMS I.20269-007, 253 mm SL, Norfolk Island, E Australia, SW Pacific (Doug Hoese); C: Shoal of adult/subadult M. f. flavicaudus, Dahab, Egypt, Gulf of Aqaba, Red Sea (Kristina Vackova); D: Shoal of adult/subadult M. f. flavolineatus, associated with snappers, La Digue and Inner Islands, Seychelles, Indian Ocean proper (Massimiliano Finzi). Scale bars = 2 cm for the respective fish on top.

Figure 3. – Mulloidichthys flavolineatus flavolineatus from Wake Island. A: BPBM 4089, 286 mm SL (Loreen O’Hara); B: Adult (Phillip & Lisa Lobel); C: Several adults or subadults; one of the four fish at top right has a yellow caudal fin (Phillip & Lisa Lobel). Scale bar = 4 cm.

Figure 4. – Standard length against five morphometric characters and one meristic character in Mulloidichthys flavolineatus and the HT of M. armatus with distinction of M. f. flavicaudus and populations of M. f. flavolineatus from selected regions by different symbols. The hatched line indicates the minimum size for adult/subadult fish.

Figure 5. – Results of PCA for Mulloidichthys flavolineatus body shape showing (A) relationships between SL and the first principal component (PC1) and (B) relationships between the second to fourth principal components (PC2-4). The subspecies M. f. flavicaudus and populations of M. f. flavolineatus from selected regions are indicated by different symbols. The dashed line encloses M. f. flavicaudus and the dotted line encloses the population of M. f.flavolineatus from the entire Pacific.