First report on the occurrence of Sargassum Weed Fish Histrio histrio (Lophiliformes: Antennariidae) in Nigeria deep water, Gulf of Guinea

: We report the first occurrence of Sargassum Weed Fish Histrio histrio at Bonga Field in Nigeria Outer Continental Shelf approximately 120 km south-east of Delta State in February 2014. At high tides and under difficulty, we sampled some seaweeds in the epi-pelagic realm using a secured standard plankton net to the environmental research vessel that was cruising at a dead speed (≤4 knots). Upon examination of the weeds we collected, one adult Sargassum Weed Fish along with two gelatinous fingerlings were realised. This finding suggests the probable occurrence of more population of Sargassum Weed Fish in their macro-habitat (the Sargassum seaweeds) which are abundantly bound in the Gulf of Guinea deep waters. The specimen was photographed on-board and preserved immediately in 10 % formalin solution for a 24-h period and was thereafter reprocessed, and permanently preserved with 70 % ethanol. We recommend a major study of the marine seaweeds and their colonisers amongst Gulf of Guinea member states.


OPEN ACCESS
Sargassum weeds are bound in abundance in the Gulf of Guinea (GoG) stretch but have not been examined as habitats and niches for several marine organisms, as evident from the lack of publications. These weeds are essential habitats to lots of pelagic dwelling organisms, for example; plankton, parasitic forms, and fishes (Kingsford 1992;Wells & Rooker 2004;Rogers et al. 2010;Rampersad 2016).
The identification and conservation of essential fish habitat was advocated as prerequisite to building healthy and sustainable fisheries (Rosenberg et al. 2000). Till date, considerable works have been focused upon characterising the spatial and temporal patterns of habitat use by fishes (Lindeman et al. 2000;Wells & Rooker 2004), and these efforts have led to valuable information regarding the physical attributes and biological significance of these habitats. Unfortunately, information on habitat use of pelagic species are limited and one of such studies was carried out in the western Atlantic (Wells & Rooker 2004). The pelagic zone is typically characterised by its lack of physical structure and previous studies suggest that many pelagic organisms associate with structures such as the algal mats or seaweeds, particularly during early life stages Rountree 1990;Kingsford 1992;Wells & Rooker 2004).
This paper seeks to document the first occurrence of the Sargassum Weed Fish Histrio histrio in Nigeria deep water. We therefore, use this medium to welcome J TT collaborative work on this subject in future.

Materials and Method The Study Area
The Bonga oil field is located in Oil Mining License (OML) 118 (4 0 35'47"N, 4 0 37'27"E), Offshore-Nigeria, with the license area lying about 120 km off the Nigeria coastline ( Figure 1). The water depth of the block range from 1,000 m to 1,150 m and the Bonga field is located in approximately 1,030 m of water. The field was discovered in 1995 and began first production in November 2005.
The field is characterised by heavy precipitation and high solar radiation. The North and South Atlantic subtropical highs and equatorial low-pressure system control its climate. Rainy season is between February and November, while dry season is between December and January. During the dry season, there may be haze and thick fog at dawn due to the dust carried by the prevailing Harmattan winds. The dominant waves are large swell waves generated by the prevailing southsouth west winds offshore Nigeria. A secondary set of short wavelength waves generated by episodic surges in the southeast winds just off the Namibian coast manifest

Sampling
We sampled for aquatic weed (Sargassum seaweed) in February 2014 while conducting a major environmental study. A 55-micron mesh size plankton net was lowered onto the sea onboard an environmental vessel while cruising at a low speed of 4 knots amidst high tide. The sampler held the net against the direction of the water current (the bow heading) while securing himself with harness by the portside. The collected weeds were introduced into a small bowl and examined. Our interest was to preserve the weeds for a museum, fortunately we harvested an adult Sargassum weed fish which was immediately preserved in 10 % formalin solution for 24 J TT h. It was there after removed and washed in sea water, and again introduced into 70 % ethanol for further studies. The specimen was identified online onboard at various websites. Specimen was photographed freshly onboard. We also recorded pH, total dissolved solids, electrical conductivity, turbidity and salinity using HANNA probe and turbidometer for in situ studies. While temperature was measured using mercury in glass thermometer calibrated from 0-100 0 C (Krisson model-59). Every other parameters were measured by dipping the calibrated HANNA probe and turbidometer into the sampled sea water immediately after collection, and the corresponding values read from the digital display on the screens were recorded.

Results and Discussion
The environmental variables (Table 1) such as water temperature, pH, total dissolved solids, dissolved oxygen, electrical conductivity, turbidity and salinity had their values within tropical seas condition (EGASPIN 2002).
The classification of the specimen Histrio histrio and the common name in parenthesis is given thus (Rampersad 2016 The fish was harvested from Sargassum seaweed Sargassum fluitans which also harboured a rich community of plankton. The nature and the occurrence of the Sargassum Weed Fish is in consistency with previous reports (Wells & Rooker 2004;Rogers et al. 2010). The colonization of Sargassum mat by pelagic fishes of which H. histrio may not have been an exception was reported by Wells & Rooker (2004) from the Gulf of Mexico and Bray & Thompson (2020) from Australia.
The Sargassum Weed Fish is also known as Frogfish. Amongst its other names across the world are: Marbled Angler, Mouse Fish, Sargassum Anglerfish, Sargassum Frogfish, Sargassumfish, and Sargassum-fish (Bray & Thompson 2020). It is the only pelagic member of the frogfish family Antennariidae, which is considered an obligate associate of floating mats of the brown algae Sargassum natans and S. fluitans (Adams 1960;Pietsch & Grobecker 1987;Wells & Rooker 2004;Rogers et al. 2010). Only one adult form and two gelatinous fingerlings were harvested from the weed colonies. Before now, there was no report on the occurrence of this fish in the Gulf of Guinea.
A detailed description of its reproduction, habitats and biology was published earlier (Rogers et al. 2010;McEachran et al. 2015;Rampersad 2016) based on the study from the USA, Trinidad & Tobago, the Pacific, and Nigeria most recently. The specimens (Image 1) are in conformity to the body size, colourations and habitat types by the works of the aforementioned authors. Total Dissolved Solids (mgL -1 ) 25060 Dissolved Oxygen (mgL -1 ) 3.29 Electrical Conductivity (µScm -1 ) 50120 Turbidity (

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The standard measurement (i.e., total length, TL) of the adult specimen from Bonga field, offshore Nigeria in the Gulf of Guinea was 61mm (Image 1) but could be up to 100 mm (Rogers et al. 2010). Meanwhile, the gelatinous juvenile forms were 0.8 and 0.9 cm, of which their pictures were not good enough for documentation purpose due to their denaturation upon preservation. Its distribution cut across both the temperate and tropical regions of the world, such as, the Caribbean Basin, Sargasso Sea, western Pacific, and Indian Oceans (McEachran et al. 2015) and currently in the Gulf of Guinea. Its reproduction involves courtship between the male which closely follows the female, rushing to the epipelagic region to spawn. Spawning is frequent and regular for more than a two week period. They produce eggs on the surface and have an appearance of being blunt at both ends with a slightly larger middle. After the female releases her eggs the male externally fertilises them as it is in other fishes. The Juveniles then move to depths exceeding 200m, where they feed and become adults, and thereafter return to the Sargassum weeds above. The juveniles feed on other fish eggs and small crustaceans, amphipods, decapods, euphausids and shrimps, whereas adults feed on other fish and shrimps among the seaweed at the surface (Rampersad 2016). On its biology, Rampersad (2016) reported again that the sargassum fish can hold the ciguatoxin poison, accumulated from its food, and can cause ciguatera poisoning in humans. This could be one of the reasons while the species is of Least Concern on the IUCN Red List (McEachran et al. 2015) and importantly, its population thrives since it is not consumable by humans. The habitat and ecology correspond to what we observed and documented at Bonga field in the Gulf of Guinea. Whereby they usually find refuge in the floating Sargassum seaweed mats which can cover a depth of 0-5 m. In these Sargassum mats, adults and eggs can be found but, the larvae of the species usually develop in water columns between 50-600 m (McEachran et. al. 2015;Rampersad 2016).
In conclusion, we strongly believe that there could be more to learn from Histrio histrio if given the opportunity to carry out a major study regarding species diversity, community structure, its seasonal preference and occurrences in the Gulf of Guinea member states. Since, the species is not documented in FAO book of fishes of economic importance and it is of Least Concern on the IUCN Red List, it is therefore crucial to understand its biology and tropical ecology as well as population in addition to existing documentations. This will further tell whether it is threatened in this region owing to increasing deep sea anthropogenic activities or not.