What species make up the Nike fish assemblages at the macrotidal estuary in Gorontalo Bay, Indonesia?

Introduction

Estuaries are a crucial habitat for biota and small fish, in particular juveniles of commercially relevant species. They are considered as the most productive and dynamic ecosystem in the world (Cantera & Blanco, 2001; Lahjie et al., 2019; McHugh, 1967; Sreekanth et al., 2017). They also perform the most crucial role in the population dynamic for a lot of invertebrate and fish species. These ecosystems also significantly contribute to provide some ecological services such as nursery ground, feeding ground and breeding habitats for both freshwater and marine species (Beck et al., 2001; McLusky & Elliott, 2004; Sun et al., 2019). The most well-known species that occupy the seas and estuary area in Gorontalo Bay is Nike fish.

Nike (pronounced nee-K) is a local name for transparent juvenile of unknown fish. These fish are approximately 2–4 cm in length; they appear seasonally and fished at estuary waters around the Gorontalo Bay. These juvenile fish has been fished and marketed traditionally for a long time. They are preferable for consumption by the local people than other fisheries products. As a consequence, fishing activity has increased over time to supply local demand for Nike (Wolok et al., 2019).

However, the impact of fishing activities is unknown. A recent paper concerning Nike only reports the seasonal appearance during the fishing season (Pasisingi & Abdullah, 2018), total length and morphometric measurements (Zakaria, 2018), nutrition content (Liputo et al., 2013), and mercury contamination of these fish (Salam et al., 2016). To our knowledge, no studies have documented the species diversity that composed the schooling of Nike. Although, Yamasaki et al. (2011) have reported that species in juvenile form can be determined by its melanophores pattern and genetic determination.

The objective of the present study is to address this lack of knowledge by identifying the fish species that composed a Nike fish schooling. This information is very urgent and required for fisheries management. Therefore, we aimed to identify the species that composed the schooling of Nike fish in Gorontalo Bay by melanophores pattern and genetic identification.

Methods

This study was conducted in October 2018 at Leato (0°30’0.58”N, 123°3’55.42”E), Gorontalo Bay, Indonesia (Figure 2). Approximately 100 g of the Nike-Fish Assemblages (Figure 1) were collected randomly from the fishermen’s catch at fishing grounds during the catch-season (on October 5^th–11^th). All samples were transported using a cool-box to the lab for measurement. Immediately after collection, all samples were identified visually according to Yamasaki et al. (2011). and the specimens with different melanophore patterns were separated according to their melanophore display. We assummed that those separated individuals were diferent on species.

Figure 1. Nike fish assemblages.

Figure 2. Study site.

The red dot indicates the position of fishing ground where the samples were collected from fishermen.

Then, we selected one individual from each group and labeled these as N1, N2, N3, N4, N5, for genetic identification. Images of the selected samples were captured using Canon EOS 100d with 58 mm pro Digital Wide Converter 0.45X Lens and subsequently converted to black and white using CorelDraw Graphic Suite 2019.

After selection, all of the individuals with different melanophores were preserved with ethanol 70% in a separate bottle and sent to the Genetics Laboratory at Manokwari for genetic identification by Sanger sequencing. The DNA cytochrome oxidase subunit I (CO1) of the sample was isolated with a Geneaid™ DNA Isolation Kit. Editing, and proofreadingof seqeunces,, and construction of the the phylogenetic tree was generated with MEGA 5.0 software.

Results

Five unspecified individuals of Nike-fish were identified morphologically by melanophore differences, as shown in Figure 3. N1 was revealed as Sicyopterus pugnans; N2 as Sicyopterus cynocephalus; N3 and N5 as Belobranchus segura; and N4 as Bunaka gyrinoides. The specimens with melanophores differences of each group is shown in Figure 4.

Figure 3. Nike fish with different melanophore patterns.

Figure 4. Phylogenetic tree of individuals with different melanophore patterns.

Discussion

Although the melanophore patterns in N3 and N5 are different, their genetics are identical, meaning they are the same species (Belobranchus segura). This dissimilarity might be affected by the changes of melanophore during the development of the larvae. Valade et al. (2009) report that such melanophores chang on Sicyopterus langocephalus during the larvae stage. These changes could represent a problem for morphological identification. We can not count the species by morphological differences. Therefore, for the next examination we strongly recommended determining the species composition of the Nike fish schools by genetic rather than morphological identification because for that reason.

Conclusion

Our findings show that there are four species that compose Nike fish schooling. They are Sicyopterus pugnans, Sicyopterus cynocephalus, Belobranchus segura, and Bunaka gyrinoides.

Data availability