Species of the gobionelline genus Oligolepis Bleeker, 1874 (Oxudercidae) are small gobies inhabiting muddy estuaries, coastal bays and lagoons, with some extending into freshwater systems. All recognised species occur in the western Pacific and eastern Indian oceans, except Oligolepis acutipennis (Valenciennes, 1837), previously considered widespread across the Indo-West Pacific to include the western Indian Ocean. Populations from the east African coast have traditionally been assigned to this species. Phylogeographic analysis of mitochondrial COI sequences reveals two deeply divergent lineages within O. acutipennis sensu lato: one distributed from the Indian subcontinent to the western Pacific, and another restricted to east African estuaries from South Africa to Kenya. The lineages differ by 5% sequence divergence and show allopatric distributions, with no confirmed records between Kenya and western India. Males of the Indo-Pacific lineage possess small black spots on the head, jaw membranes and anterior dorsal body, which are absent in the east African lineage. Based on genetic divergence, distributional isolation and several sex-specific differences (most notably the male colour pattern), the east African lineage is described as a new species, Oligolepis goni sp. nov. We further discuss the need for genus revision, considering that species diversity within Oligolepis may be overestimated, with several nominal taxa likely representing conspecific populations of O. acutipennis sensu stricto.

We provide a comprehensive checklist and identification key of the 13 known species of clingfishes (Actinopterygii: Gobiesocidae) occurring in the Mediterranean Sea, including five species described within the last decade. The species included in this checklist are confirmed based on rigorous evidence-based records. To date, all clingfishes in the Mediterranean are native and no alien species have been recorded.

Pseudogobius youtabae sp. nov. is described from Qeshm Island, Persian Gulf. P. youtabae sp. nov. is distinguished from congeners by the combination of the following morphological characters: scales in transverse series 7 (non-overlapping vs. 8-12 scales in 6 species); predorsal scales 4-6 (non-overlapping vs. 7-11 in 8 species); operculum with just 2-4 large cycloid scales in 1 or 2 rows (non-overlapping vs. 2-4 rows of more than 4 scales in 14 species); cheek naked (vs. scaly in 2 species); teeth small and similar between rows in both jaws, no sexual dimorphism (non-overlapping vs. 14 species); and coloration pattern (non-overlapping vs. all 15 species). P. youtabae sp. nov. differs from the sister species Pseudogobius minimus (Hora, 1923) by having scales in transverse series 7; predorsal scale count 4-6; interorbital width 8.4-11.3 % of head length; the first dorsal-fin spine longest in adults, the first spine equal in length to the second spine in juveniles; suborbital sensory papillae row b end anteriorly below posterior iris; suborbital sensory papillae row d end anteriorly above upper lip near angle of jaws, preorbital rows jc and jd absent and by coloration details in alive and preserved specimens. The new species has the westernmost distribution of any known Pseudogobius species, non-overlapping with other Pseudogobius species. P. youtabae sp. nov. is also well divergent from the other Pseudogobius species by high value (10-23 %) of the K2P genetic distances in the mtDNA COI barcode region being 10 % between P. youtabae sp. nov. and P. minimus.

The present research provides the first quantitative comparison of the hidden fish assemblages in Posidonia meadows and neighboring non-Posidonia habitats. The data and samples were collected at sixty sampling points at three locations on the south side of Bra & ccaron; Island in the eastern Adriatic Sea from October 2023 to June 2025. The gradient of a significant increase in fish abundance and average fish species richness in cuboids and the increase in the frequency of occurrence of fish species were observed from habitats inside Posidonia meadows, over the Posidonia meadow edge, to the habitats outside Posidonia meadows. The primary influence on the abundance was the rarity of species from the family Gobiidae within Posidonia habitats. The markedly different species composition between the Posidonia and non-Posidonia habitats was driven by the high species richness of the family Labridae in the Posidonia habitat compared to the high species richness of the family Gobiidae in the non-Posidonia habitats. The Posidonia meadow edge showed overlap with the two other habitat types, sharing a number of species. The sampling protocol developed in this study is suitable for the quantitative assessment of fishes inhabiting hidden Posidonia microhabitats and provides a methodological basis for future research. The current knowledge of fish in Mediterranean Posidonia meadows, as well as the conservation consequences of still limited knowledge, are discussed.

A new species of goby, Vanneaugobius longignathus sp. nov., is described from S & atilde;o Tom & eacute; Island, eastern tropical Atlantic. The new goby belongs to the Gobius-lineage (Teleostei, Gobioidei, Gobiidae). Examination of the two known specimens showed a unique combination of morphological characters. The new species differs from both other Vanneaugobius species by each of the following characters: head wide and depressed, anterior tip of the mouth above the level of the edge of the lower eye, posterior angle of jaw ending posteriorly below posterior iris, suborbital longitudinal row b anteriorly ending distaly behind the vertical of the posterior edge of eye, no transverse rows c above or below row b, six suborbital transverse c rows of sensory papillae, suborbital longitudinal row d divided, anterior dorsal transverse row o distant at the dorsal midline from the equivalent row. The genera Vanneaugobius and Wheelerigobius are redescribed, and, based on molecular phylogenetic evidence and reassessment of morphological characters, Vanneaugobius canariensis is reassigned to the genus Wheelerigobius.

Individuals of sand goby, Pomatoschistus minutus (Pallas, 1770), were photographed underwater in their natural habitat at Breivika, Norway, from October 2022 to January 2023. Of the 67 individuals collected, 58 were subsequently confirmed in the laboratory as P. minutus. Quantified coloration profiles were generated and statistically tested for the influence of substrate type, depth, time of day (daylight vs. night-time), and the sex and developmental stage of the individuals on the in situ coloration variability of P. minutus. Lateral body coloration showed a significant difference across bottom substrates but no significant difference for the factors of sex, developmental stage, time of day, or depth. Dorsal body coloration showed no significant difference across substrates, sex, or developmental stage; however, a significant difference was found for depth and time of day. This study provides the first detailed description of the live coloration patterns of P. minutus in its natural habitat, including a documented analysis of its qualitative variability in relation to background substrate. The found coloration plasticity highlights a sophisticated and rapid adaptation for crypsis. The ability to adjust coloration to both substrate and light conditions likely represents a significant survival strategy for this small, benthic fish against visual predators.

Among the 64 native Mediterranean gobies (Gobiidae and Oxudercidae), a rather high number of species was historically considered rare, and until today, some of these species have only a limited number of published records with a positive identification. Reviewing published data and applying quantitative thresholds shows that out of the 64 native species, 25 remain rarely recorded and can be considered elusive. Additional 13 species had been considered rare historically or just a decade ago. However, the increasingly high number of publications on gobies since the turn of the century revealed that the latter ones now have to be considered rather common. Almost all elusive gobies appear to be restricted to northern and eastern Mediterranean areas. The four areas with the highest elusive species richness showed no clear biogeographic pattern. Rather, an increased diversity counts of elusive gobies are likely sampling artifact of a high level of research activity in these areas. Almost all elusive Mediterranean gobies are very small littoral fish with no recognizable general preference for a specific bottom habitat or depth range. The best available published source was used to review and discuss the rarity of Mediterranean fishes in general. However, most of the elusive and potentially rare Mediterranean fish species lack a review of all their positive published records that would allow quantified discussion and conclusion on their elusiveness.

The checklist of 34 marine gobiid species (Actinopterii: Gobiidae and Oxudercidae) with confirmed records is compiled for the Atlantic coast of Europe, including four alien gobiid species found in transitional waters or in the low salinity waters of the Baltic Sea. An identification key for the gobiid species known from the area is also provided. The latitudinal distribution of native goby species in this area is presented and discussed. Finally, the second northernmost record of a Gobiidae fish is reported, corresponding to Pomatoschistus minutus (Pallas, 1770) from Tromsø, Norway.

New data on the recently described goby Pomatoschistus nanus Engin & Seyhan, 2017 from the Mediterranean are presented. The species is identified through genetics, morphology and coloration. Data from Malta and Cyprus significantly extend the known distribution area of the species. The Malta data also extends the upper bathymetric limit as well as the maximum known size for the species, currently considered the smallest in the Mediterranean. The morphological variability of P. nanus is also discussed.

Gobies (Gobiidae) are well represented in the Marchica Lagoon on the Moroccan Mediterranean coast, both in terms of species richness and in terms of abundance, with the black goby, Gobius niger Linnaeus, 1758, being the dominant species. The present study aims to examine (1) the spatial and temporal distribution of G. niger and its environmental drivers in the lagoon and (2) the potential lagoon -related footprint using morphometric, genetic, and parasitological proxies. Systematic monthly sampling covering the whole lagoon basin performed between October 2015 and September 2016 revealed a year -long presence of G. niger throughout the lagoon with significantly low densities in winter. The highest abundances were recorded in the shallow bottoms of the lagoon's inner margins on a variety of substrates (mud, muddy -sand, sandy -mud, and fine sand) mostly covered by macroalgae and/or seagrass meadows. Depth was revealed to be the most important predictor of the distribution of the black goby in the lagoon. It should, however, be regarded as a variable that acts synergistically with other factors, such as temperature, vegetation cover, and the sediment's mean grain size. Comparison of black goby populations from the lagoon with their conspecifics from the adjacent Mediterranean coast of Morocco revealed that specimens caught at sea are larger than those of the lagoon population. Of the 180 gobies investigated, not a single one hosted the parasites we targeted in the parasitological approach, monogenean flatworms. The absence of population structuring, low genetic diversity, and the presence of common haplotypes indicate no apparent restriction in the gene flow between the two populations. Therefore, the observed morphometric differences seem to be due to external environmental conditions rather than genetic differences.

The head lateral-line system (HLLS) is one of the most useful external characters for the taxonomy of gobies, but it is complex and, therefore, difficult to exploit. Sanzo's system was published in 1911 and has remained until today the only universal and complete system of classification and nomenclature both for the head lateral-line canals with pores and for the sensory papillae rows of gobies in general. It was based on the study of Mediterranean and European Atlantic marine gobies. Today, the native species count of the area is four times larger than the 17 species studied by Sanzo and the number of genera is 2.5 times larger. In more than a century of application, Sanzo's classification and nomenclature for taxonomy has never been reviewed or updated despite numerous published inconsistencies, conflicts and proposed individual changes. Thus, a review of HLLS of the Mediterranean and European Atlantic native marine gobies covering all genera and species of these marine areas is presented here. It is based on the evaluation of published descriptions of HLLS of native marine gobies of these seas in combination with the new data based on new material. For some species and for the genus Crystallogobius Gill, 1863, HLLS was studied for the first time and also the HLLS nomenclature was applied to some other taxa for the first time, although a sketch of the head lateral line system had been published before for those. Based on the HLLS review, a revised, simplified and consistent classification and nomenclature is presented for Mediterranean and European Atlantic marine gobies which takes into account the increased variability and complexity found over the last century; and it attempts to both consolidate nomenclature and to maintain stability, appreciating the long and widespread use of Sanzo's original system until today. Careful adaptations of the original system include: The graphemes in names of pores and of rows are now in the normal line of type only. The graphemes in names of pores and of rows are kept in italics for distinguishing them from the rest of the text in HLLS descriptions. The names and abbreviations of head canals established in the last half of century are kept. Sanzo's use of Greek letters for names of canal pores is preserved, changed only in selected cases, expanded in order to enable unique identification of pores present in neozoan species for Europe and changed to remedy the use of the same Greek letter for different pores. Sanzo's original topographical grouping of sensory papillae rows in seven head areas remained the same. The use of the same letter as a name previously applied consistently for different sensory papillae rows is replaced by a different letter. These row names are either based on letters (English alphabet), which had not already been used by Sanzo, or alternatively, they are a combination of two letters, with rows sharing the first one only if closely related. Row names with a letter followed by a number for distinguishing rows are kept only for rows typically or originally occurring as a single row, which appear longitudinally divided or transversely multiplied. Papillae appearing on the place of a secondarily lost canal, usually larger and individual, are named differently from other rows. The main goal of this revision is to update a highly useful tool for the practical identification of a valuable set of characters in gobiid systematics and taxonomy. It is not intended as a contribution to general goby anatomy.

Fishes in marine caves have attracted limited attention by the scientific community in comparison to subterranean fishes which have lost eyes and pigmentation. They constitute a largely unexplored component of marine fish diversity, except for the relatively well-studied marine caves of the Mediterranean Sea. These habitats are characterized by steep environmental gradients of decreasing light and decreasing water exchange. The fishes recorded so far in marine caves are not exclusive residents of this habitat and they are also present at least in the other mesolithial habitats. In the Mediterranean marine caves, 132 fishes have been recorded to date, representing about 17% of the total Mediterranean fish species richness. Most of these species are reported from the anterior cave zones where some light still exists, while a smaller number of species are known from the totally dark zones. Among them, 27.3% are accidental visitors, 53.8% are the regular mesolithial visitors and switchers between mesolithion and open water, 5.3% are permanent residents of the mesolithion, but also occur in other habitats, and 13.6% are exclusive permanent residents of mesolithion. Some mesolithial exclusive permanent residents recorded in marine caves share similar morphology, probably as adaptations to these habitats.

The present research quantitatively compared the fish composition among two methods for non-cryptic benthic fish species and one method for cryptobenthic fish species for the first time for the Mediterranean temperate reef fish assemblage. A visual census of fishes was performed within a cylinder of 4 m radius and within a cylinder of 2 m radius, while the cryptobenthic fishes were collected using a square of 1 m2 with anesthetic. The data and material were collected at fifty sampling points. The visual census methods together recorded 31 species, and the square with anesthetic method recorded 18 species. The quantitative comparison of methods of visual census and cryptobenthic fish collecting showed significantly different species richness, total fish abundance, and fish assemblage structure among methods. The applied methods were highly complementary. The cylinder of 2 m radius is well suited for epibenthic fishes and the cylinder of 4 m radius is reliable for hyperbenthic and benthopelagic fishes. Therefore, each of the methods well covered one of three components of ichthyobenthos (hyperbenthic, epibenthic, and cryptobenthic fishes), and all three methods together provided a far more complete assessment of fish species composition than any individual census method for the Mediterranean littoral benthic fishes.

During their radiation, certain groups of animals evolved significant phenotypic disparity (morphological diversity), enabling them to thrive in diverse environments. Adaptations to the same type of environment can lead to convergent evolution in function and morphology. However, well-documented examples in repeated adaptations of teleost fishes to different habitats, which are not primarily related to trophic specialization, are still scarce. Gobies are a remarkable fsh group, exhibiting a great species diversity, morphological variability, and extraordinary ability to colonize very different environments. A variety of lifestyles and body forms evolved also in European lineages of gobies. We conducted two-dimensional geometric morphometric and phylomorphospace analyses in European lineages of gobies and evaluated the extent of convergent evolution in shape associated with adaptation to various habitats. Our analyses revealed the change in shape along the nektonic-cryptobenthic axis, from very slender head and body to stout body and wide head. We showed convergent evolution related to mode of locomotion in the given habitat in four ecological groups: nektonic, hyperbenthic, cryptobenthic, and freshwater gobies. Gobies, therefore, emerge as a highly diversified lineage with unique lifestyle variations, offering invaluable insights into filling of ecomorphological space and mechanisms of adaptation to various aquatic environments with distinct locomotion requirements

A large sample of 65 individuals of the recently described goby Zebrus pallaoroi was collected in France. The species identity of these individuals was confirmed based on morphology. In addition, the species identity was validated through genetic analysis for one of the two specimens collected from the new depth records for the species. The diagnostic characters of Z. pallaoroi, originally based on a limited number of type specimens, were tested on this larger sample and critically analyzed. The diagnostic characters of Z. pallaoroi were revised, and recommendations were made for improving the study of diagnostic characters in gobiid species description, particularly when based on small sample sizes. The record of Z. pallaoroi in the western Mediterranean significantly expands its known geographic range, increases the maximum recorded depth of the species, and reveals syntopic co-occurrence with its phylogenetically closest relatives.

After the description of Gobius incognitus Kovačić & Šanda, 2016, all previous knowledge about the geographic distribution of Gobius bucchichi Steindachner, 1870, as well as its ecology and biology, became obsolete, since it represented the data from the mixture of two species. The known geographic distribution of G. bucchichi and G. incognitus is revisited by validating previously published records, but also and foremost by integrating many new photographic records posted by anglers and divers on social media and on citizen science databases. The present research uses only positively identified records with exact data on locality, coordinates and date of collecting. A total of 1024 confirmed records were collected and retained for inferring distribution maps: 805 records of G. incognitus and 219 records of G. bucchichi. Gobius incognitus is a widespread Mediterranean Sea species with limited presence in the Lusitanian province of the Eastern Atlantic Ocean. It is absent from the Sea of Marmara and the Black Sea. Gobius bucchichi is recorded only in the eastern half of the Mediterranean Sea, from the Adriatic to the Aegean Sea, and in the Black Sea and Sea of Marmara.

Gymnesigobius medits is reported for the first time after a recent description recorded from the Balearic Islands and from the slope of the Gulf of Vera on the Iberian Peninsula coast. The record from the Emile Baudot seamount on the Balearic Islands represents the deepest positive benthic gobiiform species record in general. The presence of the membrane connection between the pelvic fins in Gymnesigobius medits, presumed on the damaged fin in the original description, was confirmed. The recently described Gobius xoriguer is the first record from the Pitiusas and Columbretes islands and from the Iberian Peninsula coast. It appears to be widely distributed in the circalittoral bottoms, preferentially in red algae beds. Morphological identification of both species was confirmed using molecular analyses based on the sequencing of the mitochondrial cytochrome c oxidase subunit I (DNA barcode) gene. The deepest records of gobiiform fishes in oceans and seas are reviewed. The European seas, a well-studied area with eight gobiid species recorded deeper than 200 m, show high bathyal gobiid species richness compared to other areas. The real worldwide diversity of bathyal gobies, although only a fraction of the shallow water species richness of this taxon, is probably much larger than presently known.

Knipowitschia is a sand-goby genus historically comprising 17 species. The congeneric Knipowitschia species show discordance between morphology and genetics in two ways: the morphologically similar species that are clearly distinct by genetics and the morphologically and ecologically distinct populations that are similar by genetics. A sample of Knipowitschia individuals has been collected from Karpuzçay Creek on the Levantine Sea coast. It is the easternmost Mediterranean record of any Knipowitschia, and a number of arguments suggest it is native. Among the presently valid Knipowitschia species, the population was identified by both genetics and morphology as K. caucasica. The detailed morphological description and genetics are provided for this population. The morphology of the present sample fits within the highly variable morphology of east Aegean populations presently recognized as K. caucasica, although with the extreme values of the already known morphological and coloration variability.

The Western Atlantic goby Ctenogobius boleosoma (Jordan & Gilbert, 1882) was found at the Agri River mouth, south Italy. It is the northwesternmost record of an alien goby recorded in the Mediterranean Sea. The present record confirms the presence of C. boleosoma in the Mediterranean Sea, recently reported only by the DNA barcoding of larvae collected in the mesopelagic depths of the Levant Sea. The present record of adult individuals, including ripe females, indicates an established population present in shallow estuarine waters matching the species’ native habitat conditions. The morphology and coloration of Mediterranean C. boleosoma are described and discussed. A detailed description of the cephalic lateral-line system of C. boleosoma is given for the first time. Ten species of the Mediterranean alien gobies are most likely Lessepsian migrants. Three gobiid aliens are Indo-Pacific gobies not present in the Red Sea and probably introduced by shipping. The alien gobies include only one Atlantic species and the Eastern Atlantic ingression component is lacking compared to the other alien fishes in the Mediterranean Sea. Indo-Pacific gobies have been quite successful in the colonization in Mediterranean and in the establishment of the Levant populations. However, contrary to other alien fishes, gobies show limited distribution across the Mediterranean Sea, with almost all alien gobies still being restricted to the Levant.