Ryan Mohammed

A Survey of Freshwater Fish Distribution in Tobago, West Indies

The freshwater fish of Tobago were reported by a number of researchers between 1910 and 1998, wit... more The freshwater fish of Tobago were reported by a number of researchers between 1910 and 1998, with differing species richness and diversity being listed by each. Results of the recent survey reported here serve to update this baseline. Surveys were conducted at 81 sites in Tobago over the time period 2004 to 2015, with observations being conducted both nocturnally and diurnally. The most widespread species was Sicydium punctatum (Gobiidae). The species with the highest abundance was Poecilia reticulate (Poeciliidae), and the rarest species was Gobiesox nudus (Gobiesocidae). Micropoecilia picta (Poeciliidae), Ctenogobius boleosoma (Gobiidae), and Synbranchus mamoratus (Synbranchidae) were documented for the first time for Tobago. The ichthyofaunal richness for the survey now stands at 13 species. The drainage with the greatest species richness was Roxborough River, with 9 species noted.

Download

New and Updated Records of Terrestrial and Freshwater Gastropod Molluscs for Tobago, West Indies

by Mike Rutherford and Ryan Mohammed

In June 2012 and March 2013 fieldwork in Tobago was conducted, investigating the presence and dis... more In June 2012 and March 2013 fieldwork in Tobago was conducted, investigating the presence and distribution of terrestrial and freshwater molluscs. During these visits several species that have not been previously recorded from the island were observed and one species that has not been recorded within at least the last three decades was observed. Tobago has a fairly depauperate gastropod molluscan fauna when it comes to the land and freshwater ecosystems with approximately nineteen species from ten families for the terrestrial snails (Robinson et al. 2004) and ten species from seven families for the freshwater species (Bass 2003). In this note we report on six new records representing five new species (Figure) and two new families. The Helicinidae snail Helicina nemoralis Guppy, 1866 is known from Trinidad and northern Venezuela but is rarely encountered as it is thought to be arboreal (

Download

Colour Variation of an Individual of Hart’s Rivulus (Rivulus hartii) found in a Habitat Rich in Polycyclic Aromatic Hydrocarbons in the Pitch Lake of Trinidad

by C. Van Oosterhout and Ryan Mohammed

Diversity of the Ichthyofauna of Estuaries in Southeastern Trinidad

by Ryan Mohammed and Wayne Rostant

Estuaries are highly productive aquatic systems. Five rivers in Guayaguayare Bay were sampled for... more Estuaries are highly productive aquatic systems. Five rivers in Guayaguayare Bay were sampled for fish by seining. During the survey, 25 species in 21 families representing eight orders were collected or observed. The most abundant species, Mugil curema, accounted for 56% of total catch. For the majority of species encountered, the size-frequency distributions revealed populations comprised largely of subadults and juveniles. Dissimilarity of inventories between sites may be related to a combination of biotic and abiotic factors. It is proposed that each species is maintained over the entire coastline by a series of incompletely independent populations and that these estuaries collectively represent one large metacommunity.

Download

2014 The Herpetofauna of Southeast Trinidad, Trinidad and Tobago

by Ryan Mohammed and John C. Murphy

Download

Additional Observations on the Distribution of Some Freshwater Fish of Trinidad and the Record of an Exotic

Over the last decade, we have sampled various rivers across Trinidad using multiple techniques in... more Over the last decade, we have sampled various rivers across Trinidad using multiple techniques including seining and cast netting. This allowed us to compile a large database which includes the distribution of Trinidad's freshwater fish species. The following report summarizes our findings for the changed distribution for nine species of fish native to Trinidad. Our findings also indicate a new fish species (Trichogaster trichopterus) record for Trinidad.

Download

Colour Variation of an Individual of Hart’s Rivulus (Rivulus hartii) found in a Habitat Rich in Polycyclic Aromatic Hydrocarbons in the Pitch Lake of Trinidad

Getting into hot water: sick guppies frequent warmer thermal conditions

by Ryan Mohammed and Jo Cable

Oecologia, Jan 10, 2016

Ectotherms depend on the environmental temperature for thermoregulation and exploit thermal regim... more Ectotherms depend on the environmental temperature for thermoregulation and exploit thermal regimes that optimise physiological functioning. They may also frequent warmer conditions to up-regulate their immune response against parasite infection and/or impede parasite development. This adaptive response, known as 'behavioural fever', has been documented in various taxa including insects, reptiles and fish, but only in response to endoparasite infections. Here, a choice chamber experiment was used to investigate the thermal preferences of a tropical freshwater fish, the Trinidadian guppy (Poecilia reticulata), when infected with a common helminth ectoparasite Gyrodactylus turnbulli, in female-only and mixed-sex shoals. The temperature tolerance of G. turnbulli was also investigated by monitoring parasite population trajectories on guppies maintained at a continuous 18, 24 or 32 °C. Regardless of shoal composition, infected fish frequented the 32 °C choice chamber more often t...

Investigation of factors affecting the prevalence of selected parasites and bacterial pathogens on three species of freshwater catfishes exported from Trinidad

The Distribution of the Frog Eleutherodactylus johnstonei (Amphibia:Eleutherodactylidae) in Trinidad, West Indies

... Calling and reproduction occurs through-out the year however, reproduction is highest during ... more

Malaysian Prawns, Macrobrachium rosenbergii, Trinidad's Invasive Alien; Biological Indicator or Aquaculture Species?

An update of the distribution of Macrobrachium rosenbergii indicates a distribution within ten ri... more An update of the distribution of Macrobrachium rosenbergii indicates a distribution within ten rivers, in comparison to two rivers as previously documented. These rivers have higher dissolved oxygen concentrations in comparison to those where they have not been collected. With this in mind it is proposed that this species could possibly be regarded as a biological indicator species in Trinidad. They have been found in low densities and it is presumed not to be an ecological threat to native species of aquatic fauna particularly other Macrobrachium species.

Download

New Records of Two Freshwater Gastropod Molluscs for Trinidad, West Indies

Download

Update of Freshwater Turtles' Distributions for Trinidad and Possible Threat of an Exotic Introduction

Caribbean affairs (Port of Spain, Trinidad and Tobago)

The distribution patterns for Kinosternon scorpioides scorpioides is now inclusive of the western... more The distribution patterns for Kinosternon scorpioides scorpioides is now inclusive of the western portion of Trinidad. So too Rhinoclemmys punctularia punctularia's distribution pattern has widened to include a greater southern area. Mesodemmys gibbus is still the rarest of all three aquatic species. There is now threat of naturalization of a fourth species, Trachemys scripta elegans which is native to the southern region of North America. Reports of their escapes as well as wild sightings across Trinidad are documented. INTRODUCTION Murphy (1997) has the most comprehensive distribution and description of Trinidad and Tobago's herpetologi-cal fauna. Boos (2001) has since addressed the snakes of the twin islands and Manickchan (2004) has addressed the Order of Anurans (frogs and toads) within Trinidad. We now aim to update Murphy's 1997 distribution of Trinidad's freshwater turtles (Order: Chelonia). The high diversity and number of the island's wetland habitats, ...

Download

Possible return of the Driftwood Catfish, Trachelyopterus galeatus (Family: Auchenipteridae

The mean freshwater and riverine ichthyofaunal species richness for Trinidad and Tobago, accordin... more The mean freshwater and riverine ichthyofaunal species richness for Trinidad and Tobago, according to Phillip (1998), was calculated to be 38.7 using a wide range of species richness estimators, with the recorded observed being 38 fish species. Since then there have been numerous taxonomic disputes causing this richness estimate to change. Mohammed et al. (2010) documented an additional species, the gouramy, Trichogaster trichopterus in the south-central Oropuche drainage of Trinidad. Prior to this, Kenny (1995) reported 43 freshwater fish species listed for Trinidad and Tobago. In this account, the historical occurrences of the elongate hatchetfish, Triportheus elongatus (Family: Characidae) and driftwood catfish, Trachelyopter-us galeatus (Family: Auchenipteridae) were noted, but both were suspected to be extinct. Neither species were reported in Phillip's (1998) account, and subsequently were absent in the taxonomic keys for freshwater fishes by Phillip and Ramnarine (2001). ...

Download

New and Updated Records of Terrestrial and Freshwater Gastropod Molluscs for Tobago, West Indies

In June 2012 and March 2013 fieldwork in Tobago was conducted, investigating the presence and dis... more In June 2012 and March 2013 fieldwork in Tobago was conducted, investigating the presence and distribution of terrestrial and freshwater molluscs. During these visits several species that have not been previously recorded from the island were observed and one species that has not been recorded within at least the last three decades was observed. Tobago has a fairly depauperate gastropod molluscan fauna when it comes to the land and freshwater ecosystems with approximately nineteen species from ten families for the terrestrial snails (Robinson et al. 2004) and ten species from seven families for the freshwater species (Bass 2003). In this note we report on six new records representing five new species (Figure) and two new families. The Helicinidae snail Helicina nemoralis Guppy, 1866 is known from Trinidad and northern Venezuela but is rarely encountered as it is thought to be arboreal (

Download

Infestation of Hoplias malabaricus (Teleostei, Characiformes, Erythrinidae) with Nematode Parasite Eustrongyloides spp. in the Arena Dam of Trinidad, West Indies

We document the incidence of Eustrogyloides sp. and Contracaecum sp. in Hoplias malabaricus (Guab... more We document the incidence of Eustrogyloides sp. and Contracaecum sp. in Hoplias malabaricus (Guabine or Wolf Fish) for the first time in Trinidad. The drought conditions noted at the time may have contributed to the infection of these fishes. This parasite has the potential to infect waterfowl and other piscivorous birds, as well as being a potential zoonotic agent.

Collections of Freshwater Mussel Shells of Anodontites sp. and Mycetopoda sp. in Rivers of South-Central Trinidad, West Indies

Freshwater mussels belong to the family Unionidae (Order Paleoheterodonta, Suborder Unionidea). T... more Freshwater mussels belong to the family Unionidae (Order Paleoheterodonta, Suborder Unionidea). This family also includes some brackish water species. Their substrate requirements are quite varied and range from soft clays to pebbles and cobble. The family has a worldwide distribution. Members of the Unionidae family are filter feeders and this makes them quite susceptible to bio-accumulation of many residual compounds such as heavy metals. Pathogenic bacteria also form pools of infections in these filter feeders. Nonetheless, they are very important to the ecology of a river for several reasons. Firstly, the overall filtering effect of colonies decreases turbidity in the river. Secondly, because of their high sensitivity to pollution, they are used worldwide as bio-indicators. Finally, their life cycles are complex and some species rely on host fish to support the newly hatched larvae (Cummings et al. 1997). The shells of freshwater mussels were found during May, 2007 at three sepa...

Download

Additional Observations on the Distribution of Some Freshwater Fish of Trinidad and the Record of an Exotic

Over the last decade, we have sampled various rivers across Trinidad using multiple techniques in... more Over the last decade, we have sampled various rivers across Trinidad using multiple techniques including seining and cast netting. This allowed us to compile a large database which includes the distribution of Trinidad's freshwater fish species. The following report summarizes our findings for the changed distribution for nine species of fish native to Trinidad. Our findings also indicate a new fish species (Trichogaster trichopterus) record for Trinidad. INTRODUCTION The three most recent accounts of local freshwater fish distributions include Kenny (1995), Phillip (1998), and Ramnarine and Phillip (2001). Distributions outlined by Kenny (1995) had been based on extensive sampling over almost two decades prior to publication, while the distributions indicated in the latter two works draw from Phillip's national survey which spanned the years 1996-1997 and covered 22 sites across Trinidad. Kenny (1995) divided the drainage systems and the associated ichthyofauna of Trinidad ...

Download

Diversity of the Ichthyofauna of Estuaries in Southeastern Trinidad

Estuaries are highly productive aquatic systems. Five rivers in Guayaguayare Bay were sampled for... more Estuaries are highly productive aquatic systems. Five rivers in Guayaguayare Bay were sampled for fish by seining. During the survey, 25 species in 21 families representing eight orders were collected or observed. The most abundant species, Mugil curema, accounted for 56% of total catch. For the majority of species encountered, the size-frequency distributions revealed populations comprised largely of subadults and juveniles. Dissimilarity of inventories between sites may be related to a combination of biotic and abiotic factors. It is proposed that each species is maintained over the entire coastline by a series of incompletely independent populations and that these estuaries collectively represent one large metacommunity.

Download

Upstream guppies (Poecilia reticulata, Peters, 1859) go against the flow

Biota Neotropica, 2012

Guppies (Poecilia reticulata Peters 1859) in lakes and from captive-bred populations are predicte... more Guppies (Poecilia reticulata Peters 1859) in lakes and from captive-bred populations are predicted to show little rheotaxis compared to conspecifics in a stream environment that are regularly exposed to flash floods associated with involuntary downstream migration. Here we test this hypothesis using an artificial stream, examining guppies of two wild riverine populations, one lake population, and one ornamental strain. Guppies from the most upstream riverine habitat show the most pronounced rheotaxis and are less likely to be swept downstream during flooding events. However, there is no significant difference between guppies from the lowland riverine habitat, the Pitch Lake and ornamental strain. We propose that station-keeping behaviours are most strongly selected in the upstream population because large spatial differences exist in ecology and environment between up-and downstream habitats. Given that these sites are separated by barrier waterfalls that prevent compensatory upstream migration, natural selection operates particularly strong against upstream guppies that have been displaced downstream during flooding events.

Download

Uploads

Papers by Ryan Mohammed

Log In