World Aquaculture - September 2023

WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2023 51 trunk ring; the tail length (TaL), the distance from the mid-point of the last trunk ring to the tip of the tail; the standard length (SL) as the sum of HL, TrL and TaL; the dorsal fin length (DL), the distance between the anterior and posterior insertion points of the fin rays; the coronet height (CH), the diagonal distance from the mid-point of the cleithral ring to the median groove of the coronet; the snout length (SnL), from the tip of the snout to the anterior side of orbit (eye socket); the snout height (SH), the distance between the dorsal and ventral surfaces at the middle point of the snout; the orbital diameter (OD), between the anterior and posterior inside edges of the orbit; the postorbital distance (PO), from the posterior edge of the orbit to the mid-point of the cleithral ring; and the head height (HH), from the point behind the coronet to the point behind the cheek spine (Figure 3). We estimated the growth rate during development by fitting the linear regression model Y = a + bX, to the data of age (days) (X) and SL (Y) (mm), where a is the intercept and b is the growth coefficient. To evaluate the presence of different stages during the early development of the juvenile Pacific seahorses, we calculated the inflection points where the slope of growth in SL changed. We used t-tests to verify if the two slopes differed significantly (van Snik et al. 1997). After the verification of the presence of inflection points during development, we wanted to estimate the changes in the growth rate of the measured body segments during each developmental stage, which was made using the power function (Y = aXb), where SL was the independent variable (X) and the body segment was the dependent variable (Y). The value of b indicates the growth coefficient. When b =1 an isometric growth is present, but, if b <1 or b >1 then, a negative or a positive allometric growth is observed, respectively. Meaning that this particular body segment grows at a faster rate (positive allometry) or a slower rate (negative allometry) than the SL. This is a fairly simple and interesting approach to detecting changes in body form during early development, which may reveal different developmental stages, and each one may have different biological, physiological, and behavioral capabilities. Discussion The newborn Pacific seahorses showed the typical seahorse body form resembling a small adult, and yet, some of the body proportions looked very different than the adult individuals. For instance, the head seems very large, and the tail looked smaller than in larger juveniles. Nevertheless, the young seahorses show all the typical characteristics used to identify the species, for instance, the 19 rays in the dorsal fin, and the 16 rays in the pectoral fin, were present. The full number of trunk and tail rings were observed (11 and 39, respectively). Also, two trunk rings and one tail ring supported the dorsal fin. Only the cheek (1) and the eye (1-2) spines appeared later in development. The newborns had an initial SL of 7.50 ± 0.12 mm (mean ± Std Dev) and 0.0010 ± 0.0001g weight. After birth, the seahorses showed dynamic growth and drastic changes in body shape (Figure 4), particularly during the first days, and at the end of the study period (day 30) the average SL was 32.658 ± 3.58 mm with an average weight of 0.0723 ± 0.0254 g. The relationship between SL and weight during the initial development of H. ingens is shown in Figure 5, in which the growth coefficient (b) is equal to 2.93, indicating nearly isometric growth. On the other hand, the relationship between age and SL showed three lines of regression, each with a different slope separated by an inflection point; indicating the presence of three stages of development (Figure 6). The first stage of development was observed from birth and lasted until day 10. It comprised juveniles with an SL ranging from FIGURE 4. Development of the juvenile H. ingens from day 0 (newly born) to 30 days. Photo by R. P. FIGURE 5. Relationship between SL and weight during the early development of H. ingens. FIGURE 6. Standard length during the early development of juvenile H. ingens. Three developmental stages are observed. Stage I from day 1 – 5; Stage II from day 6-15 and Stage III from day 16 onwards. Data represent the mean (n = 9) for each sampling day. (CONTINUED ON PAGE 52)