Revalidation and redescription of Serranus knysnaensis Gilchrist, 1904, (Perciformes: Serranidae) with a new distribution record

A southwestern Indian Ocean (SWIO) percoid fish Serranus knysnaensis Gilchrist, 1904, was long synonymised with the comber, Serranus cabrilla (Linnaeus, 1758), from the eastern Atlantic Ocean, Mediterranean and Black Sea. However, when the species was brought out of synonymy by Heemstra & Heemstra (2004), reasons for this decision were not given. This study aims to revalidate the present taxonomic status of S. knysnaensis using morphological and molecular assessments. The two species are distinguished by the number of circumpeduncular scales (26–34 in S. knysnaensis versus 34–38 in S. cabrilla) and total gill rakers (18–22 versus 22–24). Serranus knysnaensis is also distinct from S. novemcinctus Kner, 1864, the other SWIO species of Serranus, based on total gill raker counts (18–22 versus 31–35). Genetic analysis of mitochondrial DNA barcode (COI) sequences for 17 Serranus species revealed three closely-related monophyletic clusters corresponding to S. cabrilla, S. novemcinctus and S. knysnaensis that were supported (P <0.001) by species delimitation methods. Even though the genetic distances among the three species were the lowest in the genus (1.60−1.99%), these species may be ecomorphs or lineages that have only recently diverged from each other. These three species also have allopatric distributions and our morphological and molecular data thus confirm that S. knysnaensis is a valid species.

Histopathological alterations in the gills of banded gourami (Trichogaster fasciata) exposed to thiamethoxam

Thiamethoxam (THM) is a widely used agro-pesticide in Bangladesh, though European Union has banned this neonicotinoid insecticide due to its toxic effects on non-target organisms. A 60-day experiment was conducted to study the effect of sub-lethal concentrations of THM on gills of Banded Gourami Trichogaster fasciata. The experiment was conducted in 15 PVC tanks each containing 100L water. The 96-h LC50 value of THM was estimated as 161.06mg/L for Banded Gourami. Based on estimated 96-h LC50 value, the experiment was carried out using a control (0 mg/L of THM) and five sub-lethal concentrations (9.37, 18.75, 37.5, 75 and 150 mg/L of THM in water) with three replications. For collection of gills, fishes were sampled on day-30 and day-60 of exposure to THM. Several histopathological changes were observed in the gill tissues of treated fishes viz. clubbing and reduction of gill filaments, telangiectasis of gill lamellae, haemorrhage and damage of gill raker. Water quality parameters (e.g. DO, pH and temperature) were recorded every 15 days interval. The DO levels were found to decrease significantly with increasing THM concentrations and time of exposure, whereas no noticeable changes were observed for pH and temperature. Therefore, neonicotinoid crop insecticide like THM is capable of damaging gill tissues of an small indigenous fish Banded Gourami.

Morphological divergences as drivers of diet segregation between two sympatric species of Serrapinnus (Characidae: Cheirodontinae) in macrophyte stands in a neotropical floodplain lake

Diet and morphology of Serrapinnus notomelas and Serrapinnus sp.1 were investigated across ontogeny, as a way to elucidate the key elements linked to the resource partitioning (a main driver for species coexistence). Fish sampling was conducted monthly between October 2010 and March 2012. Individuals were captured, identified, and classified into juvenile or adult. Our results show ontogenetic and interspecific differences in feeding abilities and morphological traits. Differences in body shape (relative area of the dorsal fin, length of head, height of the caudal peduncle, the aspect ratio of the pectoral and pelvic fin) favored divergent swimming performances (more maneuverability in S. notomelas and continuous swimming to Serrapinnus sp.1). We also observed divergences in trophic apparatus traits and correlations with different diets. In this context, it is highlighted that understanding the relationship between morphology and diet can assist in elucidating the processes that permeate the coexistence between sympatric species, and between ontogenetic periods. Besides, the relevant contribution of the measures of the trophic apparatus (gill raker length, the number of teeth cuspids, and intestinal coefficient) in trophic segregation seems to be a strong evidence in favor of the proposed discriminatory and predictive capacities of these traits.

Mandarin fish (Sinipercidae) genomes provide insights into innate predatory feeding

Mandarin fishes (Sinipercidae) are piscivores that feed solely on live fry. Unlike higher vertebrates, teleosts exhibit feeding behavior driven mainly by genetic responses, with no modification by learning from parents. Mandarin fishes could serve as excellent model organisms for studying feeding behavior. We report a long-read, chromosomal-scale genome assembly for Siniperca chuatsi and genome assemblies for Siniperca kneri, Siniperca scherzeri and Coreoperca whiteheadi. Positive selection analysis revealed rapid adaptive evolution of genes related to predatory feeding/aggression, growth, pyloric caeca and euryhalinity. Very few gill rakers are observed in mandarin fishes; analogously, we found that zebrafish deficient in edar had a gill raker loss phenotype and a more predatory habit, with reduced intake of zooplankton but increased intake of prey fish. Higher expression of bmp4, which could inhibit edar expression and gill raker development through binding of a Xvent-1 site upstream of edar, may cause predatory feeding in Siniperca.

Sphyraena stellata, a new barracuda from the Indo-Pacific, with redescriptions of S. helleri Jenkins, 1901 and S. novaehollandiae Günther, 1860 (Perciformes: Sphyraenidae)

A new barracuda, Sphyraena stellata, is described on the basis of 41 specimens [98.0–587.0 mm standard length (SL)] collected from the Indo-Pacific. The new species can be distinguished from all congeners in having the following combination of characters: one gill raker on first gill arch; pelvic-fin insertion located slightly before vertical through first dorsal-fin origin; pored lateral-line scales 134–141 (modally 137), total lateral-line scales 139–148 (146); scales above and below lateral line 15–17 (15) and 14–16 (15), respectively; snout comparatively short, its length 13.6–15.8 (mean 14.4) % SL; upper jaw short, its posterior tip not reaching to below anterior nostril, its length 10.0–12.2 (10.8) % SL; eye small, orbit diameter and depth 4.3–7.0 (4.9) and 3.9–5.6 (4.5) % SL, respectively; anal-fin base shortish, its length 6.9–8.1 (7.5) % SL; last dorsal- and anal-fin ray lengths 4.0–5.6 (4.7) and 3.6–5.6 (4.6) % SL, respectively; anus not close to anal-fin origin, anterior and posterior margins of former to anal-fin origin 7.5–11.9 (9.9) and 5.2–8.3 (6.8) % of head length, respectively; head sensory canal pores on suborbital area simple or slightly branched, their lowermost parts not close to margin of lacrimal bone, large smooth area lacking canal pores on mid-margin of lacrimal bone; two yellow stripes on lateral surface of body (remaining as black stripes in preserved specimens); and caudal fin gray. In addition, S. helleri Jenkins, 1901 and S. novaehollandiae Günther, 1860, both being closely related to the new species, are redescribed on the basis of 4 (243.3–545.8 mm SL) and 15 (270.8–598.0 mm SL) specimens, including holotypes, respectively, with new diagnostic characters proposed for both species.

A new species of anchovy, Encrasicholina sigma (Teleostei, Clupeiformes, Engraulidae), from Sulawesi, Indonesia

The new anchovy Encrasicholina sigma n. sp. is described on the basis of 20 specimens collected from Sulawesi, Indonesia. Although the new species can be distinguished from all other congeners except for Encrasicholina pseudoheteroloba (Hardenberg 1933) by having a long upper jaw reaching to posterior margin of preopercle, dorsal and anal fins with two unbranched rays, an exposed bony urohyal, and spine-like scutes on the abdomen, E. sigma is distinguished from E. pseudoheteroloba by lower total gill-raker counts on the first, second, third, and fourth gill arches, and on the posterior face of the third gill arch (37–42, 31–35, 18–23, 16–20, and 4–7, respectively vs. 45–55, 34–45, 22–29, 19–25, and 4–9 in E. pseudoheteroloba) and a longer head (25.2–27.0% of SL vs. 22.8–27.5%) and shorter anal-fin base (12.9–14.8% of SL vs. 13.8–18.7%).

Stolephorus babarani, a new species of anchovy (Teleostei: Clupeiformes: Engraulidae) from Panay Island, central Philippines

The new anchovy Stolephorus babarani n. sp. is described on the basis of 26 specimens collected from Panay Island, central Philippines. The new species closely resembles Stolephorus bataviensis Hardenberg 1933 and Stolephorus baweanensis Hardenberg 1933, all these species having a long upper jaw (posterior tip extending beyond posterior margin of preopercle), and numerous dusky spots on the suborbital area (in adults), snout and lower jaw tip. However, the new species differs from S. bataviensis by usually having the posterior tip of the depressed pelvic fin not reaching to vertical through the dorsal-fin origin (vs. extending beyond vertical through dorsal-fin origin), a shorter head (23.9–25.5% of standard length vs. 25.3–28.0%), and a greater distance between the dorsal-fin origin and pectoral-fin insertion (D–P1; 133.9–151.8% of head length vs. 109.9–136.3%). Stolephorus babarani is distinguished from S. baweanensis by having a shorter snout (3.6–3.9% of standard length vs. 3.8–4.6%). Moreover, the new species can be distinguished from S. bataviensis and S. baweanensis by higher gill raker counts on the first and second gill arches (16–18 + 21–23 and 10–13 + 18–21, respectively, vs. 14–17 + 19–22 and 9–12 + 17–20 in S. bataviensis and 14–17 + 19–22 and 9–12 + 17–21 in S. baweanensis). Stolephorus babarani is separated by 5.3% and 10.7% mean p-distances in the mitochondrial COI from S. baweanensis and S. bataviensis, respectively.

Sardinella alcyone n. sp., a new sardine (Teleostei: Clupeiformes: Clupeidae) from the northwestern Pacific Ocean

The new sardine Sardinella alcyone n. sp. is described on the basis of 19 specimens collected from the Ryukyu Islands, Japan and southwestern Taiwan. The new species closely resembles Sardinella pacifica Hata & Motomura 2019, both species having lateral scales with centrally discontinuous striae, a dark spot on the dorsal-fin origin, the pelvic fin with 8 rays, deciduous body scales, and very similar numbers of prepelvic and postpelvic scutes, scale rows in the longitudinal series, and pseudobranchial filaments. However, the new species is distinguished from S. pacifica by having lower total gill-raker counts on the first, second, third and fourth gill arches, and on the posterior face of the third gill arch (99–112, 97–115, 79–98, 62–77, and 25–31, respectively, vs. 112–137, 112–148, 95–127, 78–106, and 30–43), and greater pectoral fin (20.7–23.4% SL vs. 18.2–20.8%), pelvic fin (11.9–13.1% SL vs. 10.3–11.9%), maxilla (10.8–12.4% SL vs. 9.3–10.9%), lower jaw (11.8–13.4% SL vs. 10.4–11.6%), and pre-anal-fin length (77.4–82.3% SL vs. 72.9–79.3%) proportions.

A functional trade-off between trophic adaptation and parental care predicts sexual dimorphism in cichlid fish

Although sexual dimorphism is widespread in nature, its evolutionary causes often remain elusive. Here we report a case where a sex-specific conflicting functional demand related to parental care, but not to sexual selection, explains sexual dimorphism in a primarily trophic structure, the gill rakers of cichlid fishes. More specifically, we examined gill raker length in a representative set of cichlid fish species from Lake Tanganyika featuring three different parental care strategies: (i) uni-parental mouthbrooding, whereby only one parental sex incubates the eggs in the buccal cavity; (ii) bi-parental mouthbrooding, whereby both parents participate in mouthbrooding; and (iii) nest guarding without any mouthbrooding involved. As predicted from these different parental care strategies, we find sexual dimorphism in gill raker length to be present only in uni-parental mouthbrooders, but not in bi-parental mouthbrooders nor in nest guarders. Moreover, variation in the extent of sexual dimorphism among uni-parental mouthbrooders appears to be related to trophic ecology. Overall, we present a previously unrecognized scenario for the evolution of sexual dimorphism that is not related to sexual selection or initial niche divergence between sexes. Instead, sexual dimorphism in gill raker length in uni-parental mouthbrooding cichlid fish appears to be the consequence of a sex-specific functional trade-off between a trophic function present in both sexes and a reproductive function present only in the brooding sex.