# Stiphodon atropurpureus

Stiphodon atropurpureus, commonly referred to as the Philippine neon goby or blue neon dwarf goby, is a ray-finned fish of the Gobiidae family. It is native to parts of Asia, including the Philippines, China, Japan, Vietnam and Indonesia.

## Description

S. atropurpureus has a fusiform body. It measures between 20 and 50 millimeters. The two dorsal fins have seven spines in the front and nine soft dorsal spines in the back. The visual characteristics are similar to other Stiphodon species with which it shares habitat, making identification difficult without detailed anatomical study or genetic testing.
Males display a spectrum of metallic lustre that range from green to blue to purple. This iridescence is most noticeable when the fish are engaged in behaviors such as mating displays or defending their territory. The male's first dorsal fin lacks elongation and a fibrous texture, but features a distinctive narrow red border, enhancing its visual appeal to other fish and playing a critical role during social interactions.
Females are lighter in coloration compared to the males, exhibiting sexual dimorphism. Typically, their bodies are white or a light pastel hue and are marked by two clear transverse lines that run across their bodies. These lines provide them with a protective advantage by reducing their visibility to predators.
The developmental journey from juvenile to adulthood is marked by significant changes, particularly in coloration. Juveniles start with more muted tones, which gradually develop into the vibrant colours seen in adults. This progression is especially pronounced in males, as the intense coloration gained in adulthood plays a vital role in their social interactions and reproductive success.

## Distribution and habitat

S. atropurpureus is found in a variety of locations across Asia, including the Philippines, China, Japan, Vietnam and Indonesia. These gobies prefer the clear and oxygen-rich waters of faster streams, which provide not only the necessary environmental conditions for their survival, but also the substrates essential for their feeding habits. Despite the broad geographic range, the specific details of their population dynamics are not well-documented. The challenges posed by their small size and elusive nature make comprehensive population studies difficult. Research efforts are generally localized, focusing on small-scale stream surveys, which do not provide a complete picture of their overall distribution.
S. atropurpureus coexists with other species within the Stiphodon genus, which share similar habitats and ecological niches.

## Reproductive behavior and life cycle

S. atropurpureus undergoes a complex life cycle that is amphidromous (including migration from fresh water to the sea, or vice versa, but not for the purpose of breeding). Adults breed in freshwater environments, where they lay their eggs. After hatching, the larvae drift downstream to the marine environment, living planktonically. This marine phase is crucial as it allows the larvae to grow away from the competitive and predatory pressures of the freshwater environment. As they reach the post-larval stage, they begin their journey back to freshwater streams. This migration is significantly aided by their specialized adaptation of fused pelvic fins. These fins form a suction disc that enables the young gobies to cling to rocks and other surfaces, helping them to swim against the current and navigate back to their natal streams. This life cycle is essential for maintaining the genetic diversity and resilience of their populations.

## Feeding

S. atropurpureus primarily feeds on algae and biofilms, which they scrape from rocks using their subterminal mouths. This diet is rich in nutrients and the availability of food sources is impacted by the water quality in the surrounding environment.

## Conservation

Growing popularity of S. atropurpureus in the aquarium trade has raised awareness of the species, although it has also led to increased harvesting from the wild (since there is currently no dedicated aquaculture for breeding S. atropurpureus, all individuals in the aquarium trade are collected from the wild.) This practice puts more pressure on natural populations and can deplete local populations.
Furthermore, research on their abundance and distribution remains limited, complicating efforts to monitor the species.
Moreover, the species' requirement for high water quality and the requirement for migration to breed makes it vulnerable to human impacts such as dam construction, water pollution, and climate change. This species' high sensitivity to water quality and its inability to breed in polluted waters means that local populations could rapidly decline if the streams they inhabit are contaminated. Additionally, since their ability to migrate freely between freshwater and marine environments can be hindered by obstacles like dams and water diversions, which disrupt natural water flow and degrade stream environments, they significantly affect the survival and reproductive success of this species. Habitat threats like water pollution, construction projects, and climate change can alter the water clarity, temperature, and the flow rate necessary for their migration and survival.
S. atropurpureus is categorized as Least Concern (LC) by the IUCN.