COPEPODS-PARASITES OF THE GENUS MERLUCCIUS FROM THE ATLANTIC OCEAN

3 species of parasitic copepods were found on Atlantic hakes caught off the western coasts of Europe, Africa, the Medi­ terranean Sea (off Alexandria), and North America. The species are: Chondracanthus fnerluccii, Brachiel/a merluccii and Parabrachiella australis. The parasites importance as indicators of the affinities between hakes is discussed. Various hypotheses concerning the origin of the genus Merluccius are presented.


INTRODUCTION
Studies on parasites as biological indicators of their host's population status, affinities, migrations, origin and zoogeographic distribution are a valuable method to explain many problems of biology of fish.The parasitic species of a narrow specificity are particularly interesting as indicators.The parasitic copepods of the genera Chondracanthus, Brachiella and Parabrachiella appear to play such a role in hake.
During the investigations on species variability within the genus Merluccius from the Atlantic and Mediterranean Sea (Soliman, 1973), the parasitic copepods were collected in order to utilize them as possible indicators of specific affiliations and affinities between the hakes investigated.

MATERIALS AND METHOD
The parasites were collected in 1971 � 1973 from mouth and gill cavities of the fishes exami1ied.
Table 1 and the chart enclosed (Fig. 1) summarize number of fishes examined, fishing grounds and catching time of particular hake stocks.As a whole, 3 following parasitic copepod species were found: l.Chondracanthus merluccii (Holten, 1802) Kroyer, 1837; 2. Brachiella merluccii Bassett-Smith, 1896; 3. Pai"abrachiella aust r alis Wilson, 1923.All the species are specific for the genus Merluccius.The degrees of infestation in particular hake populations are presented in Table 2.Both the incidence and intensity of invasion are determined from numbers of females encountered since the dwarf males of these species usually live attached to females and rather easily fall away.

DESCRIPTION OF PARASITES FOUND
Chondracanthus merluccii (Holten, 1802) ( Chondracanthidae, Chondracanthinae ).The parasites occur in the mouth cavity of fish, attached to upper and lower jaws posteriorly behind the teeth; exceptionally they are encountered in the gill cavity.Dwarf males are attached to ventral side of females near the genito-abdomen (Fig. 2, a,b ).
The species occurs typically in the Atlantic hakes.Holten (1802) described it in Merluccius ssp.from the Atlantic and Mediterranean.According to Yamaguti (1963), the species was recorded also on Merluccius hubbsi in Brasil by Paiva Carvalho (1951)

and on
Mc<ipensis in Angola by Nunes-Ruivo (1936).Recently Ho (1971, 1974)  The species discussed occurred most frequently on the Atlantic hakes examined.Only Mm.atlanticus was free from this parasite, but a small number of fishes of this subspecies available to examination could possibly account for that (Table 1).
Mm.senegalensis off the Mauretania coasts show the strongest infestation, while the parasite seems to withdraw fromM.m.capensis.(Lernaeopodidae, Clavellinae ).The parasite occurs on the hake gm attached to tops of gill rakers (Fig. 2,c).
B.merluccii is specific for the East Atlantic hakes.Basset-Smith described it from Gad us merluccius ( = Merluccius merluccius) off Plymouth, while Brian (1906) found it in the Mediterranean Sea and Nunes-Ruivo (1956) off Angola.Ho (1974) considers the species to be typical of M.merluccius and Mcapensis.Kirtisinghe (1964) exeptionally found B.merluccii on Johnius diacanthus (Lac.)from• Pearl Banks off Ceylon.
Too small number of individuals found does not allow to conclude on variability of the species, but a great size diversity is striking.Specimens from M.m.atlanticus were at least twice as large as those from Mm.capensis.The latter exhibited also the smallest degree of infestation indicating to a tendency of losing B.merluccii as it was the case in Chondracanthus merluccii.
All the specimens were found on tops of gill rakers which are their characteristic locality indicated by• Basset-Smith in his original species description.Wilson, 1923 (Lernaeopodidae, Clavellinae).The species is typical of Mm.capensis; Wilson described it from Cape Colony.The male is usually found attached dorsally to a female thorax.The parasites live of f fish gill filaments (Fig. 2,d).

Parabrachiella australis
According to Kabata (1970), the genus Parabrachiella as created by Wilson (1915) is invalid, consequently the species P.australis should be transferred to the genus Brachiella as Brachiella australis (Wilson, 1923) Kabata, 1970.The decision, however, needs further detailed morphological studies; thus in the present paper the original name given by the author of the species is maintained.
Our own materials come from M.m.capensis caught off the Angola coasts.As a whole, 40 females and 18 males were encountered (Table 2).
Out of the three parasitic copepod species found on Mm.capensis, P.australis plays a dominating part .. Soliman (1973), basing on detailed biometric and osteologic analyses concluded, as some authors previously did, that the genus Merluccius inhabiting the East Atlantic from the European coasts to the South Africa splits into different local populations, i.e., geographic races of at most subspecies level.He distinguishes between M.m.atlanticus, Mm.mediterraneus, M.m.senegalensis, Mm.capensis, and M.m.paradoxus.

Greater differences on the specific level, particularly those in skull and otoliths enable us to regard Mbilinearis as a separate species.
Although the parasitologic material collected it too scarce to allow a firm generaliza tion, is seems to confirm Soliman' s conclusions.Such highly selective species as Chon dracanthus merluccii occurs in mouth cavities of hake from both the West (M.bilinearis,Mhubbsi) and East Atlantic (M.m.meditemzneus, M.m.senegalensis, and Mm.capensis) .
Close affinities between the Atlantic hakes and their origin from a common stem are thus evidenced.
No individuals of Ch.merluccii were found on Mm.paradoxus, the southernmost subspecies which was free from other parasitic copepods too.On the other hand, the Atlantic hakes specific differentiation is reflected in the remaining copepods.The West-Atlantic hakes from both the northern and southern hemispheres contain Brachie/Ja lageniformis (Szidat, 1955(Szidat, , 1956;;Ho, 1974) Ho (197 4) promotes the Atlantic origin of the genus Merluccius.In his opinion the North Atlantic is the ancestral habitat of hake, M.bilinearis from the eastern coasts of North America being the original species: Other hake species, both the Atlantic and Pacific ones, spread and evolved from this point according to Ho.
Mbilinearis is a host of two highly specific parasites: Ch.merluccii and B.lageniformis; Chondracanthus has not changed during the hake evolution, while Brachiella merluccii has replaced B.lageniformis in the East-Atlantic hakes.The Pacific hakes tend to lose their specific parasite Ch. merluccius, while Brachiella evolves into a new species.
However, the question of hake origin and phylogenesis remains still open; further detailed studies are necessary, both from the ichthyologic and parasitologic point of view, to elucidate the problem.

Fig. 2 .
Fig. 2. Parasitic copepods of l/llerlucciu3: a, b.Ch0i: 1dracanthus mevluccii; c.Brachiella mer!uccii; d.Parabrachiella australis , while B.merluccii was found on the East Atlantic hakes, the parasite tending to disappear, as mentioned above, south wards.The dominant species on M.m.capensu is Parabrachiella australis indicating to the 111ost distinct character of the subspecies, not evidenced, however, by morphometric examination.Extremely different hypotheses emerged when attempts were made to use parasitic indicators to explain the origin and evolution of1he genus Merluccius.According to Svetovidov (1948), Gadidae including the genus Merluccius appeard during the Oligocene in the Pontic basin, a remnant of the former Tethys Sea, later on spreading southwards along the African coasts of the Atlantic Ocean.The oldest fossils of the gadids from the middle Oligocene found in the central Europe and Cau.casus confirm this statement.Evdokimowa (1974) supports Svetovidov's hypothesis.The author found Ch.mer luccii, the species typical of the European and African hakes, in the Argentine hake, what in her opinion is as evidence of a close affinity between the hakes as well as the origin of M hubbsi from the South-African species, since the hakes spread southwards along the African coasts.Evdokimova states that the whole parasitic fauna of the Argentine hake, the typical species included, is relatively poor; she ascribes this fact to the distance from the centre of hake origin.Szidat (1955, 1956), basing on the parasitic fauna of Mhubbsi (the parasitic copepods included) suggests the North Pacific as the home habitat for the genus Merluccius and Mproductus as the form most closely resembling the ancestor.The hake evolution in his opinion proceeded along two paths: one running along the western coasts of North and South America to the Atlantic with M.hubbsi emerging and the other leading northwards around the North America, in the Pliocene reaching North Atlantic and giving rise to Mbilinearis and M.merluccius.Szidat assumes, among, the others, 3 species of parasitic copepods: B.lageniformis, Ch.palpifer, and Tri.fur tortuosus to be the parasitic indicators.Kabata' s (1970) finding of Brachie/Ja lageniformis on the gills of M.productus off the Canadian coasts seems to confirm Szidat 's hypothesis.