Agarna malayi, Tiwari, 1952

Aneesh, Panakkool Thamban, Sudha, Kappalli, Helna, Ameri Kottarathil & Anilkumar, Gopinathan, 2018, Agarna malayi Tiwari 1952 (Crustacea: Isopoda: Cymothoidae) Parasitising the Marine Fish, Tenualosa toli (Clupeidae) from India: Re-description / description of Parasite Life Cycle and Patterns of Occurrence, Zoological Studies 57 (25), pp. 1-22 : 14-17

Agarna malayi - Pattern of parasitic interaction

with its host fish Tenualosa toli

Eighty species of marine fishes belonging to 35 families were closely examined during the study period (November 2009 to November 2013) for the presence of A. malayi , and the parasite was recovered only from Tenualosa toli , signifying A. malayi ’s oligoxenous host specificity. Out of 485 host fish observed, 84 showed infestation with A. malayi ; a total of 156 parasites including 70 males, 77 ovigerous females, 5 transitionals and 4 juveniles were recovered from the gill chamber of infected host fish, prevalence and intensity being 17.3 and 1.86%, respectively. Parasites were usually found in pairs in the host fish, one in each branchial cavity, and, in 65 (77.4%) instances, male-female pairs were found; the relatively large ovigerous female preferred to attach to the inner wall of the operculum, close to the posterodorsal corner of the gill chamber, orienting upside down ( Figs. 1E, F , 2I, J ). Small sized males were found to occupy the opposite gill chamber more or less in the same position. In 5 occasions (6%), transitionals were also paired with males. In two cases (2.4%), paired juveniles were also found. In twelve cases (14.2%), unpaired females were found. Interestingly, the bodies of both females and transitionals showed an asymmetry in their shape inasmuch as it is hunched either towards left or right according to their occupation in the right and left branchial cavity, respectively; more than 70% (56 out of 77) of the females were recovered from the right gill chamber ( Figs. 1 , 2E, F ). The parasite occupying the branchial chamber of the host fish invariably showed the presence of a large depression and the atrophied gills, the severity of which was proportional to the size of the parasite.

In a single instance, apart from A. malayi , the host fish ( T. toli ) also showed the simultaneous infestation with another cymothoid, Anilocra leptosoma (Bleeker 1857) , which was settled on the base of the dorsal fin.

Figures

Fig. 1. Photographs of the holotype and paratype of Agarna malayi Tiwari 1952 specimens studied: (A) holotype (C3121/2) dorsal view; (B) holotype (C3121/2) ventral view; (C) paratype (C3122/2) dorsal view; (D) paratype (C3122/2) ventral view; (E) branchial cavity of Nematalosa nasus, showing the holotype (C3122/2) in situ; (F) branchial cavity of Nematalosa nasus, showing the paratype (C3122/2) in situ.

Fig. 2. Agarna malayi Tiwari 1952 ex Tenualosa toli (Valenciennes). (A-B) male dorsal and ventral view; (C-D) transitional stage dorsal and ventral view; (E-F) ovigerous female dorsal view; (G) manca II larva; (H) juvenile; (I) ovigerous female on T. toli; (J) manca II on T. toli.