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| Fig.1. The newly described Mornos Goby - Μορνογωβιός - Economidichthys mornosensis. |
A New Fish Species from Greece
Inland ichthyofaunas in Greece are more than just species lists; they are living indicators of biogeographic history. The have guided us in the study of evolutionary regional units. Their distribution and evolutionary relationships help us reconstruct geological events that shaped aquatic biota at various scales in time and space.
Yet despite decades of research, some small fish species remain taxonomically unresolved. Among them are the tiny freshwater gobies: small, morphologically subtle creatures with disproportionate biogeographic significance. They are good biogeographic indicators because they stay put - the don't migrate or disperse easily. One of them turned out to be a new species - we discribed it, published just a few days ago, we are calling it Economidichthys mornosensis - the Mornos Goby...endemic to the Mornos Delta!
The Suspicion: Something Didn’t Fit
In the 1990s, Professor P.S. Economidis (1934-2022) noted that a very small goby lived in the Mornos Delta - a delta in the huge and deep Gulf of Corinth. It resembled a species of the genus Knipowitschia, but he expressed doubts about this. Years later, genetic analyses we conducted with our Belgian partner Maarten P.M. Vanhove confirmed that the Mornos goby population was clearly distinct from known species. It does not belong to the Knipowitschia, but to the gobies of the genus Economidichthys — a group of small endemic fish of western Greece named in honor of Economidis. For many years, our fish team at HCMR, often collaborating with co-workers from abroad, has worked on these tiny goby fishes. My mentor Alcibiades Economou always thought something was worth the detective work at the Mornos Delta.
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| Fig. 2. The map in Professor Economidis's article in the periodical "Ι Physis" in 1992. It shows all the major freshwater gobies in Greece with approximate distributions known at the time. It provides an erroneous record of Economidichthys pygmaeus at the Mornos Delta and the question mark of a proposed new species there which he called Knipowitschia stephanidisi - question mark (site 9? in this map). Conclusion: many decades later...here is no E. pygmaeus or Knipowitschia (or any other small goby) at Mornos Delta - but a new very tiny Economidichthys goby (obviously, the one he called K. stephanidisi) and now we just described it new for science; as E. mornosensis. |
The Genetic Evidence
My friend, the taxonomist, naturalist, and fish celebrity, Jörg Freyhof, came in to help close the case of the Mornos Economidichthys population. We needed a complete review and survey of all populations of the related fish, the Western Greece Goby - Economidichthys pygmaeus. This included a search for the original population in the type locality - where it was first found (on Lefkada), specimens described and published back in 1929. We collected Economidichthys widely and also confirmed a population extirpation at the type locality (Lefkada Island). Within other taxonomic work we are doing along with friends from the Czech republic, we focused on resolving this problem once and for all.
First the genetics - this was already evident back in our publication with Maarten Vanhove in 2007. Using DNA barcoding (mitochondrial COI gene), our new chapter in this research confirmed a 5.7% genetic divergence from the Mornos population to its closest relative, Economidichthys pygmaeus. In fish taxonomy, a divergence of more than 2% in COI typically indicates the potential for a separate species rather than a local population variant (however opinion on such thresholds varies...anyway). The COI genetic divergence from Economidichthys pygmaeus is remarkably high despite the more widespread E. pygmaeus being found just 40 kilometers to the west (in the Acheloos - Evinos system). This divergance is well above typical intraspecific variation (~0.04% within E. pygmaeus populations). In other words, the Mornos goby represents an independent evolutionary lineage. Although related to E. pygmaeus it evolved in a different world, within a state of a high degree of isolation.
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| Fig. 3. Genetic results shown through phylogenetic analyses (ML, NJ, MP trees); A dendrogram here summarizes the relationships among sampled populations: the Mornos population forms a distinct clade (highlighted yellow), apart from the widespread E. pygmaeus populations; an even more distinctive one is Economidichthys trichonis an endemic of the Lakes Trichonis and Lysimachia. From: the paper, Freyhof et al. (2026) |
What Makes It Different?
Beyond genetics, morphology supports the Mornos Goby's distinct species status. Males show a prominent black blotch on the first dorsal fin. The perianal organ is smaller and structurally different from that of E. pygmaeus. The posterior back lacks scales at the base of the second dorsal fin.
It is also extremely small — not exceeding 4 cm in total length (TL). Even when reared in large tanks under captive conditions, individuals remained tiny, suggesting that small body size is an evolutionary trait, not just plasticity due to environmental constraint. The species is very close to the size of the smallest adult fish in Europe, the Trichonis Dwarf Goby - E. trichonis (which has an adult size of about 3 cm TL at its maximum). The closer relative, the Western Greece Goby - E. pygmaeus- is by contrast a 'giant'; we have caught several a 6 cm TL (as published in our checklist - Barbieri et al. 2015).
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| Fig. 4. Snapshots from our field aquarium studies - comparison of the three species of the genus Economidichthys (not shown exactly to scale): The Mornos Goby Economidichthys mornosensis -A,B,C (three adult males shown). The Western Greece Goby Economidichthys pygmaeus - D. The Trichonis Dwarf Goby Economidichthys trichonis - E. (Photos by S. Zogaris). |
A Species with a tiny geographical range - part of an important biogeographical unit!
The Mornos goby is a stenoendemic (i.e. a very range restricted, narrow endemic species). Based on our studies and our inventory so far, it survives only in small spring-fed wetlands within the Mornos Delta, nowhere else. Its entire distribution covers less than 5 km² and we have found it in only three water bodies in that system (actually just two in the survey of spring and fall 2025). And, there may be a biogeographical reason for this extreme range-restricted state. We did not find it anywhere else in the Gulf of Corinth basin. This is where the biogeography comes in - read on please.
The geological history of the Mornos River is critical here: the river has and always had drained into the Gulf of Corinth, which once was a lake, just before the start of the Holocene. This likely explains the species isolation and the context for its evolution into a distict species. In contrast, major river basins flowing westward into the Ionian Sea host the related Economydichthys pygmaeus - a much more widespread species because population exchanges (as did river confluences) existed among these systems - all facing sea-ward, westward. How many people know the Gulf of Cornith was not connected to the Ionian sea just 13 K years ago?
So the Gulf of Corinth freshwaters may make up a biogeographical unit of extreme conservation interest- but only its freshwater wetlands, not the marine gulf it is today....Today, most freshwater coastal wetlands around the Gulf of Corinth have been degraded or totally lost. To the east of the Gulf is a strong rain-shadow area - see Galaxidi and Corinth: dry lands and intermittent/ephemeral streams, almost seasonally-semi arid (no long-term freshwater wetlands). And humans have been activley stealing waters and wastefully destryong wetland for a long time. So, the spring-fed flowing waters on level ground, are extremely rare. Most are found solely in the Mornos Delta. The map below shows the guld and the major river basin flowing within it; the Mornos is the largest, with the largest wetland remnants at its Delta.
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| Fig. 5. Copy-paste of map of the Gulf of Corinth, with the rivers entering the Gulf - and the Mornos - the largest (blue spot; where the Delta is today - inserted by me). The Mornos therefore did not drain into the open Ionian like the other westward flowing rivers of Western Greece (i.e. Acheloos, Pineios), it entered a former Lake. The Rion Sill is only 60 m. deep; anytime global sea levels were below this depth, the Gulf was transformed back into a lake. This has been going on for at least 5 million years. Map from: McNeill, et al. 2019. High-resolution record reveals climate-driven environmental and sedimentary changes in an active rift. Scientific Reports, 9(1), p.3116. Specifically what and when was the Gulf of Corinth a Lake? Here I include references (as cited in Freyhof et al. 2026): Unlike the other large rivers along the Ionian coast, the Mornos River flows into the semi-enclosed Gulf. This gulf experienced very long periods of isolation and freshwater (lake-like) conditions starting at least in the Late Miocene (~5 Ma). Yes, at least 5 million years ago. Even more extensive lake conditions occurred during the Pliocene to early Pleistocene (~2–1 Ma) (Gawthorpe et al. 2018). Around ~1 Ma, increased subsidence and/or a lowering of the western basin threshold (the Rion Sill) allowed seawater from the Ionian Sea to enter the basin. As a result, the basin changed from a lake into a marine gulf (Lykousis et al. 2004; McNeill et al. 2019); freshwater life probably found refuge in the surrouning riparian wetlands - river mouths, springs. Later, during the Pleistocene glacial periods, global sea levels dropped repeatedly (down to ~120 m below present levels). When sea levels were low, the shallow Rion Sill became exposed, cutting off the marine connection with the Ionian Sea. During these times, the Gulf of Corinth once again turned into a very large lake basin (Perissoratis et al. 2000). After the Last Glacial Maximum, sea levels rose again and overtopped the Rion sill in the late Pleistocene (~13.5 ka before present), restoring marine conditions in the Gulf of Corinth (Mazzini et al. 2023). Because the Gulf of Corinth has had this unusual history of alternating between lake and marine conditions, and because it has long been connected to the Mornos River, freshwater environments in the area likely remained isolated for long periods (i.e. no real or ''easy'' connection to the adjacent Acheloos). This long-term isolation probably promoted vicariant separation of freshwater organisms. Such geographic isolation of freshwater ecosystems from the wider Ionian coastal region may have encouraged the local differentiation of fish species (especially poor dispersers, such as tiny gobies); maybe other aquatic species as well.
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Under Pressure
Somehow, the wetland wonders that were a refuge to this fish and other freshwater biota survived the ups and downs of a large inland lake, then a sea (back-and-forth). But, they could not easily have survived human-induced wetland and surface water ecosystem degradation (this has been going on for a long time in this 'heart of civilization' area....see Ancient Corinth etc etc).
Although the Mornos Delta is part of the Natura 2000 network, the remaining habitat faces serious pressures:
- Water abstraction and diversion from springs
- Wetland drainage and fragmentation
- Infrastructure development and scattered construction
- Increasing drought frequency
We saw and photographed in 2025: Illegal dumping, trash heaps and garbage tipping, agro-chemical pollution, embankment and drainage channel digging and clearing, wetlnad in-filling, scattered housing being built, and over-abstraction (or so it seems) from a key hotspot wetland site, immediately above the fish species stronghold (during a drought period).
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| Fig. 7. This is a pump-house immediately above the spring-fed wetland hotspot which is a critical refuge for the Mornos Goby (and other species). Please see Fig. 10 below for conditions at the wetland immediately below this pumphouse in Sept. 2025. For years we know of the pump-house, however, we know nothing of its impact on the water levels or spring flow. This area is within the heart of the Natura 2000 protected area - and area zones as highly important. No action on the ground. |
The fish and freshwater biota populations are small and fragmented. Our study suggests the Mornos Goby likely qualifies as Critically Endangered. The delta is also home to the globally threatened killifish Valencia robertae, and prorably other rare freshwater animals. We found the mussel (Unionidae)... If research continues, it could be that this area is exceptionally important for aquatic biodiversity. (Anyway, it is important).
A Small Fish, A Larger Message
The story of the discovery of the Mornos Goby reminds us that Greece’s freshwater biodiversity may still provide amazing surprises. Small and inconspicuous aquatic species are often the most vulnerable and there is no real concern for them. Scientists and naturalists must speak for them. These biota depend on fragile habitats that are easily altered or destroyed. Legal so-called protection alone is not enough. Without scientific work, active management and habitat restoration, conservation remains only “on paper.” Protecting this tiny fish means protecting an entire wetland ecosystem at the landscape scale — and the natural heritage it represents. This means an action plan and careful conservation politics - on the ground. We need to save the landscapes of the Mornos Delta and specifically help protect the spring-fed wetlands within these landscapes. Can we do it? Below I provide some important snap-shots of local conditions. First of all, please keep in mind, this area is a Protected Area....
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| Fig. 8. Within the terrestrial protected areas of the Gulf of Corinth (marine areas not shown) we have the Delta (top left) inside the SCI called PARALIAKI ZONI APO NAFPAKTO EOS ITEA - PERIOCHI PIGON CHILIADOU (GR2450004). In fact, back in 2017, we at HCMR (and with the support of a consortium surveying fish for the Natura project) expanded the protected area to include a critial spring area, the 'Periochi Pigon Chiliadou'. Our ''success'' in this really means ''nothing'' (I was responsible for delineating the new extenstion of the Natura on behalf of the fish - that, nearly 10 years ago). If you cannot promote measures on the ground you are doing practically nothing (see photos below). |
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| Fig. 9. Landscape scenes from the Mornos Delta within the Natura 2000 protected area (GR2450004). A typical agricultural-domainted, second-home building area and beach tourism hot-spot. Rapid land-use change are taking place. These photos are from Google Maps; I am not making a statement here or propagandizing, there is no conservation action for freswaters on the ground - none at all. |
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| Fig. 10. One of the most important habitats for the Mornos Goby, a spring area which I intentionally leave un-named since I a fear it may be vandalized or disturbed since, really, there is no real protection: Left: the hotspot area in Sept. 2014 and Right in Sept. 2025. I |
Our paper with the full details is available from the Authors through ResearchGate:
