Atherinella brasiliensis (Quoy & Gaimard, 1824)

França, Elton J., Severi, William, Castro, Maviael F., Medeiros, Tatiane N. & El-Deir, Ana Carla A., 2007, Description of Atherinella brasiliensis (Quoy & Gaimard, 1825) (Atheriniformes: Atherinopsidae) larvae from the Jaguaribe River estuary, Itamaracá island, Northeastern Brazil, Neotropical Ichthyology 5 (3), pp. 369-374 : 370-372

Table 1 displays the amplitude and size ranges of body proportions of

Atherinella brasiliensis

larvae and juveniles. Table 2 displays the meristic counts for selected specimens. A. brasiliensis larvae hatch at sizes smaller than 1.4 mm SL. The only specimen analyzed at this size was in the preflexion stage. The specimen could not be depicted or measured due to its distorted state, but its taxonomical status was determined by the typical pattern of head pigmentation (see below). Thus, the exact size of yolk-sac larvae could not be determined.

The preflexion stage, which lasts until the beginning of notochord flexion and formation of the hypural bones, varied from 2.3 to 4.7 mm SL (n=62, mean=3.5± 0.59 mm).At this stage, larvae are nearly completely enveloped by an embryonic membrane (finfold) along the midline of the body, which begins precisely behind the head. The pectoral fin buds (P 1) are the first to form and are located in a high lateral position on the body just behind the head ( Fig. 1a ). The larva has four characteristic dendritic chromatophores on the head – two placed anterolaterally, a third more posteriorly along the midline, forming a triangle, followed by a fourth placed further posteriorly – and pigmentation along the whole median portion of the ventral region ( Figs. 1b and c ). The number of chromatophores along the midventral line varies between 22 and 28. The caudal fin (C) supporting elements are first noticed at this stage and it is also possible to identify the position where the second dorsal (D 2) and anal fins will form. The total number of myomeres is 34, but pre and postanal myomeres are not clearly distinguished due to early development of rays. The body is elongate (14.2 to 16.1%), the head is small (18.2 to 19.9%), and the eye is large (42.2 to 53.0%).

The flexion stage ranges from 4.4 to 6.8 mm SL (n=14, mean=5.7± 0.71 mm) and is characterized by the flexion of the notochord tip. With an average size of 4.7 mm SL ( Fig. 1d ), the larva exhibits a finfold enveloping the second dorsal and anal fins, where pterygiophores can be seen. However, the rays are almost completely formed in both fins only at 6.4 mm SL ( Fig. 1e ), when larvae no longer have an evident embryonic membrane. At this size, the mouth assumes a slightly upwardly inclined terminal position. The chromatophore count varies from 29 to 30 on the midventral line. The total number of myomeres is 34 (16-17 preanal, 17-18 postanal). At this stage, the body varies from very elongate to elongate (9.8 to 15.1%), the head is moderate (20.0 to 22.9%), and the eye is large (34.9 to 50.0%).

In the postflexion stage, larval size varied from 7.4 to 11.8 mm SL (n=12, mean=9.0±1.7). The larva exhibits ossification of the second dorsal and anal fin rays. It also has pelvic fin (P 2) buds ( Fig. 1f ) located anterior to the anus. Intensification of head ( Fig. 1g ) and lateral body pigmentation is observed and is probably related to the formation of the silvery line. At approximately 12.0 mm SL, all fins are completely formed and the first dorsal (D 1), which is the last to ossify, is located in a position slightly posterior to the anal fin insertion ( Fig. 1h ). The number of chromatophores along the midventral line varies from 30 to 33, but these may be fused into a single line in some individuals at this stage. The myomeres are still visible and vary from 33 to 35, with 16 to 17 preanal and 17 to 18 postanal. The body varies from very elongate to elongate (9.6 to 16.1%), the head is moderate (23.4 to 25.4%), and the eye is large (33.3 to 40.3%).

The juvenile period in Atherinella brasiliensis may begin at approximately 12 mm SL, but sizes ranged from 11.6 to 77.0 mm (n=14, mean=36.1±24.3). The anal fin is located at the median portion of the body, slightly behind the first dorsal fin. The posterior margin of the pectorals surpasses the origin of the pelvic fins, which are located at the midpoint between the insertion of the pectoral and anal fins. Scales can be seen in the dorsal-lateral region near the head in individuals above 13.00 mm SL. Lateral pigmentation is more intense and the formation of two longitudinal rows of chromatophores can be seen. The two rows begin precisely behind the insertion of the anal fin and extend to the caudal peduncle ( Fig. 1i ). Midventral line chromatophores are fused into a single line.

All larval stages and juveniles exhibit 25 to 30 chromatophores along the midlateral line. The first appearance of fin rays in Atherinella brasiliensis follows the sequence P 1 →C→D 2, A→P 2 →D 1. A definitive number of vertebrae is attained at 7.0 mm SL, at the end of the flexion stage ( Table 2 ). Total number of fin elements is first recorded as follows: D 2 and P 2 at 10 mm (post-flexion), C at 11.5 mm (post-flexion), D 1 and P 1 at 12 mm, and A at 15.8 mm (juvenile) ( Table 2 ).

Figures

Fig. 1. Larval, transforming larval, and juvenile Atherinella brasiliensis: 3.5mm preflexion larva in lateral (a), ventral (b) and dorsal (c)views; (d)4.7 mm larva atthe beginningof flexion stage; (e)6.4mmattheendof flexion larva;(f)8.8mmpostflexion larva; (g) head view of a 12 mm transforming larva; (h) 12 mm transforming larva; and (i) 15 mm juvenile. Scale bar = 1 mm.