ABSTRACT

Aspects of the biology and conservation of Fontitrygon garouaensis in the Lokoja section of the river Niger was studied. Specimens and water samples was collected over a stretch of about 48km of the River Niger downstream of Lokoja, from the River Niger/Benue confluence to Itobe, between January 2015 and December 2017. Live specimens of the species were transported to Umudike for captive observation studies in aquariums. The elevation of the River Niger at the Lokoja section ranges from 43m (± 5m) at the confluence to 32m (± 5m) at Itobe. . A total of 34 F. garouaensis with total weight of 14,736g made up of 23 females and 11 males was collected in 36 fishing experimental fisheries. Water physicochemical parameters was sampled twice monthly for the period of study. The largest recorded individual caught in the experimental fisheries was a female 334mm DW with body weight 695g while the largest male captured was 250mm DW with body weight of 343g. Water samples were collected fortnightly from two stations in each of the three segments of the study area. Although some of the ranges showed significant difference (p>0.05), all parameters were within the range for freshwater stingray habitation. Fontitrygon garouaensis was only captured between the months of November and April which coincides with the dry season and low-water seasons. There was no catch of the fish species in the location between the months of May and October for the three years study period. The log-transformed Length–Weight relationship of male F. garouaensis was negatively correlated while the female and combined sex relationships were positively correlated at 0.05% level. (p

<0.05%). A male to female sex ratio of 1:2.7 was recorded for the period. Morphological features of F. garouaensis of the species was reported. Mean Weight ± SE (g) of 317.36 ± 30.01and 488.91 ± 30.53was reported for male and female respectively and 433.41 ± 159.71 was reported for the combined sex. Biological studies revealed a diminutive rectal gland and sexual dimorphism in the teeth structure of F. garouaensis. Insect larvae of Gomphidae (Dragonfly) and Tabanidae (Horsefly) together accounted for over 65% (IRI) of the diet of Fontitrygon garouoaensis. Dragonfly larvae (Gomphidae) was the most representative in all measured indices with 36.4(%N), 46.1(%W), 92.3(%FO), and (48.5)%IRI. In captive observation studies, the species did not show aggression to the different species added to their tank including small fishes- Alestis (A. longipinnis) and Debauwi (P. debauwi) confirming a non piscivorous diet. The results of this study point to a highly dwindled population of Fontitrygon garouaensis in the River Niger and the need for action towards the conservation of the species.>