Hydrolagus melanophasma, James, Ebert, Long & Didier, 2009, James, Ebert, Long & Didier, 2009

Donayre-Salazar, Susan, Roque-Sánchez, Máximo, Campos-León, Sarita, Sotil, Giovanna, Huamaní-Galindo, José & Béarez, Philippe, 2024, New data on the presence and biology of the eastern Pacific black ghostshark Hydrolagus melanophasma (Chimaeridae) from the Peruvian coast, Cybium 48 (2), pp. 97-109 : 101-105

RESULTS

Morphological description

Based on the examination of 16 specimens and the data gathered on this particular species, the identification of the chimaeras as Hydrolagus melanophasma has been definitively confirmed. These specimens were distinguished by their substantial and robust body, featuring a uniform black coloration that tapers towards a whip-like tail with a caudal filament. Their snout is blunt and gently sloping from the orbits to the tip. The mouth is relatively small and positioned ventrally, while the eyes are of moderate size. The pectoral fins exhibit a large, triangular anterior margin that extends to or beyond the insertion point of the pelvic fin when placed against the body. The anterior margin of the pelvic fins is straight with a convex posterior margin. The lateral line extends along the body, starting from its junction with the postorbital canal and extending all the way to the whip-like tail. The first dorsal fin takes on a triangular shape with a short base, a concave posterior margin, and a noticeable spine (though it was found to be broken in the observed specimens), whereas the second dorsal fin is elongated and of uniform height. The caudal fin features dorsal and ventral lobes of approximately equal size, and an absent anal fin. The mouth is positioned ventrally and contains three pairs of beak-like, yellowish-grey tooth plates, each with pale tritor rods. Notably, the vomerine tooth plates exhibit longitudinal tritor rods which vary in number between the sexes, females possess six longitudinal tritor rods and males have eight. The mandibular plates also have longitudinal crushing rods, which are not readily discernible for counting ( Fig. 3 ). Detailed information on the body length and proportions of the specimens can be found in Table II.

Reproductive system

Among the four males collected in this study only one was an adult, measuring 1130 mm in total length (Qui_15). This specimen exhibited strongly developed and calcified hooks (105 mm), along with the presence of a cephalic tenaculum featuring 38 spines ( Fig. 4 ), and pre-pelvic tenacula adorned with six thorn-shaped denticles ( Fig. 5A ). The remaining three males (Qui_02, Qui_07 and Qui_13) were juveniles and did not exhibit mature testis or calcified hooks ( Fig. 5B ).

Measurements of the male (Qui_07) reproductive apparatus were performed. Male testis averaged 25 mm in length, 1.4 mm in width, and the vas deferens 90 mm in length ( Fig.6A ). The females measured between 973 mm and 1378 mm TL. Gonads of two adult females (Qui_05 and Qui_06) were analysed, showing previtellogenic oocytes with diameters ranging from 1.3 mm to 8.5 mm (mean 3.8 mm). The ovaries had a mean length of 56.4 mm and a mean width of 49.7 mm. The oviducal gland had a mean length of 52.1 mm and a mean width of 24.2 mm. The uterus averaged 170.9 mm in length and 12.4 mm in width ( Fig. 6b ).

Molecular identification

Mitochondrial DNA COI (652 bp) and 16S (574 bp) sequences were obtained from the 16 specimens. For the COI gene, a mean nucleotide composition of A (25.1%), T (29.8%), G (17.0%), and C (28.2%), and only one nucleotide difference at position 625 (A/G) was observed when the sequences were compared. For the 16S, all sequences were identical, recording a mean nucleotide composition of A (31.7%), T (26.1%), G (20.7%), and C (21.4%). All the sequences obtained in this study were deposited in the GenBank database, with accession numbers from OK427213 to OK427228 (COI) and from OK427231 to OK427246 (16S).

The top hits of the COI sequences, considering the highest BLASTn scores and a query coverage of> 90, showed a 98% identity with different species of the genus, such as Hydrolagus affinis (de Brito Capello, 1868) , Hydrolagus mirabilis (Collett, 1904) , and H. trolli ; however, no accessible registered sequences for H. melanophasma were found in any public nucleotide database. Furthermore, the 16S sequences showed a 99.83-100% identity with the two records for H. melanophasma (HQ645967 and HQ645968) available from Baja California Sur, Mexico.

All the COI sequences registered under the genus Hydrolagus in GenBank (n = 23; the other 39 registered as H. ogilbyi , H. lemures and H. cf. lemures have the current status of Chimaera ogilbyi ) were selected and aligned (532 bp) with those obtained in this study. Sequences from 8 species were compared and a total of 110 variable sites were identified (with 101 PI). Comparing the sequences of H. melanophasma (from this study) with H. affinis and H. mirabilis (species with the highest scores in BLASTn), only 9 variable sites were recorded, of which 8 were PI (Table SI). On the other hand, only 12 sequences of the 16S gene (from 8 species, excluding sequence HM147139) were recovered from GenBank, registered as genus Hydrolagus . Comparing these sequences with those obtained in this study (429 bp), 38 variable sites were recorded, of which 17 were PI; however, when limiting the comparison to consider only those with the highest BLASTn hits ( H. melanophasma and H. affinis ), 3 variable sites were identified, and only 1 substitution was observed when comparing with H. melanophasma from Mexico (Table SII).

The K2P pairwise distances between Hydrolagus species, based on the COI gene, showed a difference of between 1.2% (between H. affinis and this study) and 18.1% ( Hydrolagus africanus (Gilchrist, 1922) and this study). Hydrolagus melanophasma differed from other Hydrolagus species within a range of 1.2 to 16.9% (Table III). In contrast, based on 16S rRNA, the genetic distance between H. melanophasma from this study and Mexico was 0.1%, whereas between congeneric species it was in the range of 0.1 to 5.6% (Table IV).

The phylogenetic tree, based on the COI gene, showed that Hydrolagus melanophasma formed a monophyletic clade (97% bootstrap). This species grouped closest to four species reported from the North Atlantic Ocean ( H. affinis , H. mirabilis , Hydrolagus lusitanicus Moura, Figueiredo, Bordalo-Machado, Almeida & Gordo, 2005 , and Hydrolagus pallidus Hardy & Stehmann, 1990 ) and one from the South Pacific ( H. trolli ). It is interesting to mention that only one species ( H. macrophthalmus ) from South America ( Chile) was registered in GenBank, but was clustered in a different clade together with H. africanus ( Fig. 7 ). The NJ tree based on the 16S gene sequences, showed that H. melanophasma from Peru (this study) clustered with those reported from Mexico and H. affinis (87% bootstrap), while H. mirabilis was grouped in a different clade with H. africanus and Hydrolagus cf. alberti ( Fig. 8 ).

DISCUSSION

Distribution and diversity

Hydrolagus melanophasma is known to inhabit the Tropical Eastern Pacific , spanning from California to Patagonia (Ebert, 2016). Various authors have reported and studied this species throughout the eastern Pacific, including James et al. (2009), Bustamante et al. (2012), Mejía-Mercado (2013), Aguirre-Villaseñor et al. (2013), Martínez-Ortíz and García-Domínguez (2013), Márquez-Faríaz and Lara-Mendoza (2014), Ebert (2016), Araya et al. (2020) and Giddens et al. (2020), encompassing a vast geographical range from California, USA (36°N) to Valdivia, southern Chile (40°S), including the Galapagos Islands. Records pertaining to mainland Ecuador, however, have raised some concerns. These references are based on the works of Martínez-Ortíz and García-Domínguez (2013) and Aguirre-Villaseñor et al. (2013). Unfortunately, the latter mentioned erroneous coordinates, i.e. 10°25’N; 78°52’W, which actually correspond to a location in the Caribbean Sea off the coast of Panama, not Ecuador. In addition, there appears to have been some confusion between Isla Santa Rosa (Esmeraldas, northern Ecuador) and the fishing harbour of Santa Rosa (Santa Elena, southern Ecuador) whose coordinates are 2°12’28.5”S; 80°57’W, and which is the locality referred to by Martínez-Ortíz and García-Domínguez (2013). It is therefore plausible that the specimen originated from the Gulf of Guayaquil, at around 3°S, as Aguirre-Villaseñor et al. (2013) reported that the locality was 74 km south of Santa Rosa .

In Peru, the first mention of the genus Hydrolagus was made by Chirichigno (1968), in reference to an undescribed species of an undetermined male specimen measuring 601 mm TL collected at 17°37’S- 71°35’W ( Fig. 9A ). This specimen was sent to C.L. Hubbs at Scripps Institution of Oceanography (SIO) ( Chirichigno, 1968: 396). Subsequently, Chirichigno (1974) introduced some confusion by presenting a separate drawing of a Hydrolagus specimen, possibly representing H. melanophasma ( Fig. 9B ). Although Chirichigno (1976) recorded H. macrophthalmus , they still maintained the existence of an undescribed species of Hydrolagus , whose drawing ( Chirichigno, 1976: fig. 3) corresponds to that in Chirichigno (1974: fig. 5). Unfortunately, it has never been given a scientific name by the author. Both species then appeared in successive publications by the same author ( Chirichigno and Vélez, 1998; Chirichigno and Cornejo, 2001).

One of the authors (PB) observed two large male individuals (ca. 1 m TL) in Ilo on 20 November 2007, although they could not be preserved due to their substantial size. Didier and Meckley (2009) mentioned two species off Peru: Hydrolagus macrophthalmus and Hydrolagus sp. Three individuals (522-990 mm TL; 267-545 mm BDL) of the latter were obtained between 1998 and 2003, and the authors suggested that these specimens might represent the same species as the one cited by Chirichigno (1974).

The new species was finally described in 2009 based on specimens from northern Mexico and California ( James et al., 2009), but the study did not include any specimens from Peru. Furthermore, the latest list of chondrichthyans from Peru, published by Cornejo et al. (2015), does not include Hydrolagus macrophthalmus . In Ecuador, H. melanophasma has been cited by Martínez-Ortíz and García-Domínguez (2013) and Calle-Morán and Béarez (2020), whilst in Chile it has been reported from Taltal ( Araya et al., 2020) and Valdivia ( Bustamante et al., 2012) at depths of 1150 to 1800 m ( Fig. 1 ). The specimens in this study were caught at depths between 1200 and 1700 m, which aligns with the findings of Alfaro-Shigueto et al. (2022) who reported depths between 1360 and 1618 m.

Fishery

Finucci et al. (2021) mention that chimaeras are a datapoor group, that little is known about their fisheries, and that their catches are perhaps the least reported among chondrichthyans. As far as Hydrolagus melanophasma is concerned, the species is frequently encountered in fisheries such as the Patagonian toothfish fishery operating along the western coast of South America in Ecuador, Peru, and Chile ( Finucci et al., 2021). High proportions of Hydrolagus sp. have been mentioned by Bustamante-Ruiz (1997) and Alfaro-Shigueto et al. (2022) in the Patagonian toothfish fishery in Peru. Here, we report on catches using bottom longlines equipped with rows composed of a horizontal mother line containing 900 6/0 Mustad hooks. The bait used in this fishery includes species such as Auxis eudorax Collette & Aadland, 1996 , Trachurus murphyi Nicols, 1920 and Sphoeroides spp. , in accordance with information provided by local fishermen. However, the volume of landings and discards of H. melanophasma bycatch in Peruvian deepwater longline fisheries is currently unknown and needs to be assessed.

Figures

Figure 1. – Geographic distribution map of Hydrolagus melanophasma. A: Records of the species in the east- ern Pacific Ocean based on references (indicated in triangles); B: Collection sites in southcentral Peru considered for this study.

Figure 3. – Morphology of the vomerine tooth plates in both sexes of Hydrolagus melanophasma. A: Females with six tritor rods; B: Males with eight tritor rods.

Figure 4. – Morphological characteristics of Hydrolagus melanophasma. Cephalic tenaculum in male specimen (Qui_15).

Figure 5. – Hydrolagus melanophas- ma claspers. A: Adult male-113.0 cm (Qui_15), prepelvic tenaculum; B: Juvenile male-90.6 cm (Qui_07).

Figure 6. – Reproductive apparatus of Hydrolagus melanophasma. A: Male-90.6 cm (Qui_07): (1) testes and (2) vas deferens. B: Female-122.2 cm (Qui_06): (3) ovary, (4) oocyte, (5) oviducal gland and (6) uterus.

Figure 7. – Neighbour-Joining phylogenetic tree based on the mtDNA COI gene sequences (532 bp) of genus Hydrolagus obtained from GenBank and in this study. Numbers in branches indicate bootstrap values (percentages of 1000 replicates). (*) Chimaera ogilbyi used as an outgroup.

Figure 8. – Neighbour-Joining phy- logenetic tree based on the 16S gene (429 bp) from genus Hydrolagus obtained from GenBank and in this study. (*) HM147139 H. lemures syno- nym of Chimaera ogilbyi. Numbers in branches indicate bootstrap values (per- centages of 1000 replicates).

Figure 9. – Illustration of Hydrolagus species in the previous Peruvian literature. A: Probable H. macrophthalmus (Chirichigno, 1968); B: Probable H. melanophasma (Chirichigno, 1974).