Morphological comparison of the feeding apparatus in herbivorous, omnivorous and carnivorous mudskippers (Gobiidae: Oxudercinae)

Microplastic contamination in Thai vinegar crabs (Episesarma mederi), giant mudskippers (Periophthalmodon schlosseri), and their surrounding environment from the Bang Pu mangrove forests, Samut Prakan province, Thailand

The mangrove ecosystem becomes the receptacle for both land- and marine-based plastic waste. This study examines MPs contamination in the Bang Pu mangrove forests (BPMFs) in the inner Gulf of Thailand. For this, Thai vinegar crabs (TVCs) (Episesarma mederi) and giant mudskippers (GMs) (Periophthalmodon schlosseri) were investigated with their surrounding environment in both rainy and dry seasons. Two-step digestion was employed for biota samples. MPs abundance ranged from 7.5 ± 3.8 to 15.9 ± 6.7 items/individual in TVCs and 6.2 ± 5.0 to 10.6 ± 2.6 items/individual in GMs. MPs in small-size ranges (<0.5 mm) were predominant. Fiber MPs were mostly detected in the rainy season. Most MPs were transparent with polyethylene and polypropylene as dominant polymers in all samples. Bioaccumulation was not observed in GMs. The results indicated the imperiled status of MPs contamination in TVCs and GMs with contaminated surrounding environments.

The gastric proton pump in gobiid and mudskipper fishes. Evidence of stomach loss?

Stomach loss has occurred independently multiple times during gnathostome evolution with notable frequency within the Teleostei. Significantly, this loss of acid-peptic digestion has been found to correlate with the secondary genomic loss of the gastric proton pump subunits (atp4a, atp4b) and pepsinogens/pepsins (pga, pgc). Gastric glands produce gastric juice containing the acid and pepsin and thus their presence is a hallmark feature of a digestive system capable of acid-peptic digestion. However, in gobiid fishes although oesogaster and gastric glands have been identified histologically, their functional significance has been questioned. In the present study we address whether the gastric proton pump is present and expressed in gastric glands of the goby Neogobius species (Gobiidae) and in members of the family Oxudercidae, a group of amphibious gobiid fishes commonly known as mudskippers (genera: Periophthalmus, Boleophthalmus, Periophthalmodon and Scartelaos). We confirmed the presence of gastric glands and have immunohistochemically localized gastric proton pump expression to these glands in Neogobius fluviatilis and Periophthalmus novemradiatus, Periophthalmus barbarus and Boleophthalmus boddarti. Genome analysis in Neogobius melanostomus, Periophthalmus magnuspinnatus, Scartelaos histophorus, Boleophthalmus pectinirostris, and Periophthalmodon schlosseri revealed the presence of both atp4a and atp4b subunit orthologues in all species in a conserved genomic loci organization. Moreover, it was possible to deduce that the complete open reading frame and the key functional amino acid residues are present. The conserved expression of the gastric proton pump provides clear evidence of the potential for gastric acid secretion indicating that acid digestion is retained in these gobiid fishes and not lost.

Morphological comparison of the cranial movement apparatus in mudskippers (Gobiidae: Oxudercinae)

Possession of the neck allows vertebrates to move the head independently from the trunk. Fish do not have the neck and thus the cranial mobility could be limited. Oxudercine gobies show full range of habitat transition from aquatic to terrestrial environments and exhibit flexible cranial movement, yet the cranium-movement apparatus is little known. In this study, we investigated the anatomy of the structure of the eight oxudercine gobies, Oxuderces nexipinnis, Parapocryptes serperaster, Pseudapocryptes elongatus, Scartelaos histophorus, Boleophthalmus boddarti, Periophthalmus chrysospilos, Periophthalmodon schlosseri, and Periophthalmodon septemradiatus. These species share similarities in the specialized features of the craniovertebral joint and the epaxials attaching onto different locations of the neurocranium. On the other hand, large space between the ventral portions of the craniovertebral joint only occurs in O. nexipinnis, Pd. elongatus, Pn. schlosseri and Pn. septemradiatus. Hypaxials are hypertrophied at the insertion point and attach more anteriorly onto the ventral side of the neurocranium in B. boddarti, O. nexipinnis, Pa. serperaster, Pd. elongatus, and S. histophorus, whereas the muscles are small and attach posteriorly in the remaining species. There were significant differences in the area occupancy ratio of the post-cranial neural spines, the lever arm ratio of the cranial rotation, and the angle between the horizontal plane and the plane through the craniovertebral joint among the species. The cranial depression presumably facilitates grazing of oxudercine gobies in their early stage of terrestrial transition, whereas the cranial elevation parameters are contradictory to the terrestrial gradient. The cranium-movement morphometrics partially agree with the phylogeny.