Age estimation of juvenile European hake Merluccius merluccius based on otolith microstructure analysis: a slow or fast growth pattern?

The main goal of this study was to examine otolith microstructure and to estimate the age and growth of European hake Merluccius merluccius from the eastern Mediterranean Sea. One hundred and twenty‐nine specimens ranging from 102 to 438 mm in total length (L_T) were used. Age estimations were based on the study of the otolith microstructure, which was revealed after grinding both frontal sides of otoliths. The enumerations of the daily growth increments (DGI) as well as their width (W_DGI) measurements were made on calibrated digital images. The number of DGI in otoliths ranged between 163 and 717. Four phases in the W_DGI evolution were distinguished: (1) larval–juvenile pelagic phase, with an increasing trend in W_DGI up to the 60th DGI, (2) settlement phase, with a short‐term deceleration in W_DGI between the 61st and 150th DGI, (3) juvenile demersal phase, characterized by a stabilization of W_DGI from 151st to 400th DGI and (4) adult phase, with a decreasing trend in W_DGI after the 400th DGI. Age, sex and month of formation were found to affect the W_DGI in all phases, with the exception of age at the juvenile demersal phase. The power curve with intercept model described best the relationship of M. merluccius L_T with age (T_DGI), according to Akaike criteria, revealing differences in growth between females [L_T = 65 · 36(T_DGI)^{0 · 40} ? 388 · 55] and males [L_T = 69 · 32(T_DGI)^{0 · 37} ? 352 · 88] for the sizes examined. The mean daily growth rates were 0·61 mm day^?1 for females and 0·52 mm day^?1 for males, resulting in an L_T of 283 and 265 mm at the end of their first year of life. In comparison with previous studies on the Mediterranean Sea, the results of this study showed a greater growth rate, similar to results from tagging experiments and otolith microstructure analyses for M. merluccius in other geographic areas.     

Diel vertical migrations of bathypelagic perch fry

The behaviour of young‐of‐the‐year (YOY) perch Perca fluviatilis as a dominant species in the assemblage of fry in the pelagic of Slapy Reservoir (Czech Republic), was studied during late May and mid‐June 2002 using acoustic methods and complementary net catches. During the day, perch fry were present simultaneously in littoral, epipelagic and bathypelagic habitats. Bathypelagic perch fry, forming a scattering layer, migrated vertically each day between the epilimnion and hypolimnion, with an amplitude of 11·0 m in May and 12·5 m in June. At dusk, the migratory bathypelagic fry mixed in the epilimnion with non‐migrating epipelagic fry and spent the night close to the thermocline (abundance maximum at 3–4 m in May, 0–2 m in June). In June, shoaling behaviour by some of the bathypelagic perch fry was also observed: the shoaling fry remained higher in the water column than the non‐shoaling fry. Both depths of the scattering layer and the depths of the fry shoals were strongly controlled by the light intensity. The contribution of the bathypelagic part of the population to the total numbers of pelagic perch fry decreased from 28·1% in May to 4·7% in June, while the density of all pelagic perch fry increased (c. 96 000 individuals ha^?1 in May and 142 000 individuals ha^?1 in June). In May, the bathypelagic (average total length, L_T, 11·9 mm) and epipelagic (average L_T 14·6 mm) perch fry differed in size while, in June, the epipelagic fry were divided into two distinct size groups. The more abundant group, of small epipelagic perch fry (average L_T 14·6 mm), was similar in size to the bathypelagic fry (average L_T 14·6 mm) while the less abundant group, of larger epipelagic fry (average L_T 34·4 mm), was similar in size to littoral perch fry (average L_T 35·0 mm). The results suggest that in perch fry three different survival strategies with different risks can be used in the same locality, time and year.     

Occurrence of age‐0 year dwarf pikeperch Sander lucioperca in late summer – an overlooked phenomenon in reservoirs

Late summer sampling of pelagic age‐0 year fish communities in five Czech reservoirs and one Dutch reservoir revealed extremely small age‐0 year pikeperch Sander lucioperca (mean 24 mm standard length, L_S, minimum 13 mm L_S) alongside more normal‐sized S. lucioperca that are found at the end of the first growing season (mean 50 mm L_S), resulting in two clearly size‐separated cohorts. Reference to such small age‐0 year S. lucioperca in lakes or reservoirs at this time of year and in such large numbers are almost absent the scientific literature, and the presence of these small S. lucioperca is contradictory to the common understanding of the reproductive biology of this species. This overlooked phenomenon may have a major effect on the population dynamics of this valuable species because of size‐dependent winter mortality.     

Trophic ecology of yellownose skate Zearaja chilensis,a top predator in the south‐western Atlantic Ocean

The diet and trophic level (T_L) of the yellownose skate Zearaja chilensis in the south‐western Atlantic Ocean (35°–54° S), and how these varied in relation to body size, sex, maturity stage, depth and region were determined by analysis of stomach contents. From 776 specimens analysed, 671 (86·5%) ranging from 180 to 1190 mm total length (L_T) had prey in their stomachs. The diet was dominated by fishes, mainly the notothenioid Patagonotothen ramsayi and the Argentine hake Merluccius hubbsi. The consumption of fishes and crabs increased with increasing predator size, and these preys were more important in the north than in the south. Isopods and other crustaceans were consumed more in the south and their consumption decreased as the size of Z. chilensis increased. The T_L of Z. chilensis increased with L_T from 4·29 to 4·59 (mean 4·53), confirming their ecological role as a top predator. The small and large size classes exhibited a low diet overlap and the highest spatial segregation, whereas medium and large specimens had higher co‐occurrence and dietary overlap indices. A clear distinction in tooth shape was noted between sexes in adult specimens, with males having longer cusps. This sexual heterodonty may be related to reproductive behaviour, increasing the grasping ability of males during courtship, because there were no differences in diet between the sexes.     

Thermal response of demersal and pelagic juvenile fishes from the surf zone during a heat‐wave simulation

Experimental measurements were collected in the laboratory to evaluate the maximum thermal limit and thermal plasticity of Neotropical juvenile fish with different life habitats (demersal and pelagic) from surf zone in response to a “heat‐wave experiment”. Trials were conducted using two temperature acclimations (T_a), including the current average temperature of Southeastern Brazil (T_a: 14 days at 25°C) and the “heat‐wave experiment” (T_a: 14 days at 30°C), simulating a heat‐wave event that occurs when the daily maximum temperature of more than five consecutive days exceeds the average maximum temperature by 5°C. Typical species of the surf zone were used: the demersal White sea catfish (Genidens barbus) and Gulf kingcroaker (Menticirrhus littoralis), and the pelagic fishes Great pompano (Trachinotus goodei) and Long‐fin mullet (Mugil brevirostris). The thermal range and plasticity values for the both life‐habitats species were verified through current and heat‐wave acclimation. The thermal tolerance at high temperatures (CT_max) of these species differed between T_a, habitat and species. Fish showed a species‐specific response to temperature increase, regardless of their habitat even under similar abiotic conditions. However, at the heat‐wave simulation, the demersal fish presented a greater thermal plasticity in relation to the pelagic fish. Despite the higher thermal tolerance when exposed to heat‐wave simulation, all fish species displayed a lower thermal edge safety that is markedly close to their maximum thermal limits.     

Life‐history traits and population decline of the Atlantic mackerel Scomber scombrusin the Adriatic Sea

This study investigated demographic structure and reproductive characteristics of the Atlantic mackerel Scomber scombrus, in relation to landing trends in the northern‐central Adriatic Sea. Results highlighted the occurrence of only small‐sized and young‐age individuals, and a marked decline from the 1990s to the present in maximum age (from 8 to 3 years) and total length (L_T; from 420 to 360 mm). Fecundity ranged between 40 000 and 190 000 eggs, and was related to female L_T. High levels of atresia implied lower values of actual fecundity. Sexual maturity was attained by 72·8% of individuals in their first year of life at 200 mm. The reduction in maximum L_T resulted in a marked decline in the population egg production, while the reduction in maximum age implied that females participated in fewer spawning events.     

Environmental change influences the life history of salmon Salmo salar in the North Atlantic Ocean

Annual mean total length (L_T) of wild one‐sea‐winter (1SW) Atlantic salmon Salmo salar of the Norwegian River Imsa decreased from 63 to 54 cm with a corresponding decrease in condition factor (K) for cohorts migrating to sea from 1976 to 2010. The reduction in L_T is associated with a 40% decline in mean individual mass, from 2 to 1·2 kg. Hatchery fish reared from parental fish of the same population exhibited similar changes from 1981 onwards. The decrease in L_T correlated negatively with near‐surface temperatures in the eastern Norwegian Sea, thought to be the main feeding area of the present stock. Furthermore, S. salar exhibited significant variations in the proportion of cohorts attaining maturity after only one winter in the ocean. The proportion of S. salar spawning as 1SW fish was lower both in the 1970s and after 2000 than in the 1980s and 1990s associated with a gradual decline in post‐smolt growth and smaller amounts of reserve energy in the fish. In wild S. salar, there was a positive association between post‐smolt growth and the sea survival back to the River Imsa for spawning. In addition, among smolt year‐classes, there were significant positive correlations between wild and hatchery S. salar in L_T, K and age at maturity. The present changes may be caused by ecosystem changes following the collapse and rebuilding of the pelagic fish abundance in the North Atlantic Ocean, a gradual decrease in zooplankton abundance and climate change with increasing surface temperature in the Norwegian Sea. Thus, the observed variation in the life‐history traits of S. salar appears primarily associated with major changes in the pelagic food web in the ocean.     

Reproductive biology of the crocodile shark Pseudocarcharias kamoharai

From February 2005 to September 2007, a total of 490 crocodile sharks Pseudocarcharias kamoharai, caught as by‐catch in the swordfish and tuna longline fishery that operates in the tropical western Atlantic Ocean, was studied in regard to their reproductive biology. Maximum observed total lengths (L_T) were 1220 and 1090 mm for females and males respectively, with a high proportion of the catch being composed of mature specimens. Sexual maturity was attained at 760–810 mm L_T for males (L_T50 = 800 mm) and 870–980 mm L_T for females (L_T50 = 916 mm). The size at birth was estimated at 415 mm L_T. Temporal variation in gonad morphology and mass suggests that in this region P. kamoharai, an aplacental viviparous species with oophagy, does not show a well‐defined reproductive seasonality, with mating and parturition occurring possibly over an extended period of the year. Mean ±s.d . fecundity was estimated to be 3·9 (± 0·6) pups per reproductive cycle.     

Age,growth and maturity of the pelagic thresher Alopias pelagicus and the scalloped hammerhead Sphyrna lewini

Indonesia has the greatest reported chondrichthyan catches worldwide, with c.110,000 t caught annually. The pelagic thresher (Alopias pelagicus) and scalloped hammerhead (Sphryna lewini) together comprise about 25% of the total catches of sharks landed in Indonesia. Age and growth parameters were estimated for A. pelagicus and S. lewini from growth‐band counts of thin‐cut vertebral sections. Alopias pelagicus (n = 158) and S. lewini (n = 157) vertebrae were collected from three Indonesian fish markets over a 5 year period. A multi‐model analysis was used to estimate growth parameters for both species. The models of best fit for males and females for A. pelagicus was the three‐parameter logistic (L_∞ = 3169 mm L_T, k = 0·2) and the two‐parameter von Bertalanffy models (L_∞ = 3281 mm L_T, k = 0·12). Age at maturity was calculated to be 10·4 and 13·2 years for males and females, respectively, and these are the oldest estimated for this species. The samples of S. lewini were heavily biased towards females, and the model of best fit for males and females was the three‐parameter Gompertz (L_∞ = 2598 mm L_T, k = 0·15) and the two‐parameter Gompertz (L_∞ = 2896 mm L_T, k= 0·16). Age at maturity was calculated to be 8·9 and 13·2 years for males and females, respectively. Although numerous age and growth studies have previously been undertaken on S. lewini, few studies have been able to obtain adequate samples from all components of the population because adult females, adult males and juveniles often reside in different areas. For the first time, sex bias in this study was towards sexually mature females, which are commonly lacking in previous biological studies on S. lewini. Additionally, some of the oldest aged specimens and highest age at maturity for both species were observed in this study. Both species exhibit slow rates of growth and late age at maturity, highlighting the need for a re‐assessment of the relative resilience of these two globally threatened sharks at current high levels of fishing mortality throughout the eastern Indian Ocean.     

Using scales to clarify the transition from blue-phase to brown-phase fingerling in Notothenia rossii from the South Shetland Islands

Scales and whole otoliths were read for age determination in early stages of Notothenia rossii caught in Potter Cove, South Shetland Islands, in summer seasons 2003–2006 and 2008. The sample comprised blue-phase pelagic fingerlings of 7.0–7.6 cm (TL) of age group 0 year and demersal brown-phase fingerlings/juveniles of 8.5–20.9 cm and predominant age groups 1–2 years. Counting of sclerites facilitated the interpretation of the rings, particularly in the central scale. To clarify two previous issues of controversy, we deduce that the duration of the offshore pelagic blue-phase fingerling stage is less than one year before migration to the nearshore demersal habitat. Furthermore, the first well-defined ring in scales corresponded to the first annulus, while a contiguous ring was a secondary ring sometimes deposited after the first winter during the second year of life, attributable to a shift of habitat from pelagic to demersal. A von Bertalanffy growth curve was computed by combining age/length data of the juvenile phase of N. rossii from this and a previous study at Potter Cove with literature data from the offshore adult population, resulting in the following equation: L_t = 8 6. 9  ( 1- \texte ^{- 0. 0 9 1 (t - 0. 6 6 8 )} ) L_{t} = 8 6. 9 \,\left( { 1- {\text{e}}^{{ - 0. 0 9 1 (t - 0. 6 6 8 )}} } \right) _.     

Fishery and Ontogenetic Driven Changes in the Diet of the Spiny Dogfish, Squalus acanthias, in Patagonian Waters, Argentina

The diet of the spiny dogfish in northern and central Patagonian waters was studied from the by-catch of the bottom trawling fisheries directed to Argentine hake Merluccius hubbsi and Argentine red shrimp Pleoticus muelleri between 1996 and 1998. Food habits were analyzed in relation to sex and maturity of sharks. Also, the relationship between diet and abundance of the main prey was explored. Intraspecific diet comparisons were performed. Differences in diet were found between immature individuals, mature males, and mature females. The Argentine shortfin squid Illex argentinus, the Argentine hake and ctenophores Pleurobrachia pileus were the most important prey for the spiny dogfish. Immature and small individuals were pelagic predators. After sexual maturity, the spiny dogfish shifted its diet. Mature and large individuals tended to reduce the consumption of ctenophores, and increase the consumption of demersal and benthic species. Previous diet studies on the spiny dogfish in 1984–1985 and 1994 indicated that the Argentine hake was the most important prey. In the present study, carried out in 1998, squid was the most important prey, followed by the hake. This diet change was related to the major decrease of hake due to overfishing and the increase of squid abundance between 1994 and 1999.     

Reproductive biology of the greeneye spurdog Squalus chloroculus (Squaliformes,Squalidae)

The reproduction of the greeneye spurdog Squalus chloroculus was studied based on animals caught in the multispecies and multi‐gear southern and eastern scalefish and shark fishery on the upper continental slope off southern Australia. One hundred and ninety‐nine females (502–990 mm, total length, L_T) and 189 males (515–810 mm L_T) were examined. The female reproductive cycle, based on 41 breeding animals, is continuous and triennial, with the pregnancy period estimated to be 31–34 months, seasonal and synchronous with the ovarian cycle; a third of the breeding female population is estimated to give birth between September and December each year. The estimated L_T at which 50% of females are mature is 799 mm (95% c.i. : 794, 804), whereas the L_T at which 50% are maternal is 825 mm (95% c.i. : 817–833), but these estimates are probably biased by the phenomenon of apparent change of L_T at maternity and L_T at maturity following severe length‐selective fishing mortality. Litters ranged from four to 15 embryos with a 1:1 sex ratio, and litter size increased with maternal length. The breeding cycle of males is neither seasonal nor synchronous with the female cycle. The estimated L_T of males where 50% are mature was 629 mm (95% c.i. : 603, 645).     

Biology of the kingsoldier bream (Argyrops spinifer, Forsskål 1775; Sparidae), from the Arabian Sea, Oman

It is recognized by the FAO that management of fish resources in the western Indian Ocean is complicated by the lack of data on the basic biology and landing statistics for exploited fish species. In this paper data are presented on the population biology of kingsoldier bream, Argyrops spinifer (Forsskål 1775), in the Arabian Sea with a view to contributing towards the development of management plans for its sustainable exploitation. Samples were obtained from the Omani artisanal hand‐line fishery catch, January 2001–December 2002. Total length (L_T) of fish sampled ranged from 20 to 68 cm (males) and 25 to 70 cm (females). The male : female ratio was similar up to 55 cm L_T but the larger size‐classes were composed predominately of male fish. L_T/carcass weight (W_C) relations for male and female fish were similar and the combined data produced an equation W_C = 0.00005 × L_T^2.67. Marginal increment analysis indicated an annual cycle of opaque and translucent ring formation in otoliths that was related to the change in surface water temperature during the annual monsoon period. The opaque zone was completed in May and the translucent zone began to form in June. Female and male fish age ranged between 2 and 25 years. Both males and females exhibited similar asymptotic growth patterns; the combined von Bertalanffy growth function was L_t = 64.6(1 ? e^{[?0.142(t + 0.489)]}). Gonadosomatic indices and gonad condition of male and female fish indicated that the spawning season occurred between September and January. Size (L₅₀) and age at first maturity (A₅₀) were estimated to be 36.5 cm L_T and 5.0 years for males and 37.2 cm L_T and 5.6 years females, respectively. The results of this study provide fundamental information on the biology and population dynamics of A. spinifer in the Arabian Sea that can be used in management models for the continued sustainable exploitation of this species in the Omani demersal coastal fisheries.     

Biological observations on the bristly catshark Bythaelurus hispidus from deep waters off the south‐west coast of India

Biological data are presented for the poorly known bristly catshark Bythaelurus hispidus based on specimens collected from the by‐catch of the commercial deep‐sea shrimp trawl fishery operating in the Arabian Sea at depths of 200–500 m off the south‐west coast of India. One hundred and sixty‐two individuals, which ranged from 120 to 366 mm total length (L_T), were collected for this study. Size‐at‐maturity (L₅₀) for females and males was estimated at 252 and 235 mm L_T, respectively. The reproductive mode of B. hispidus was aplacental viviparity, which is the rarest reproductive mode within the Scyliorhinidae and is considered to be the most advanced of the three reproductive modes occurring within this family. Dietary analysis of stomach contents revealed B. hispidus feeds on a variety of prey, primarily fishes.     

Reproductive biology and feeding habits of the prickly dogfish Oxynotus bruniensis

The reproductive biology and diet of prickly dogfish Oxynotus bruniensis, a deep‐sea elasmobranch, endemic to the outer continental and insular shelves of southern Australia and New Zealand, and caught as by‐catch in demersal fisheries, are described from specimens caught in New Zealand waters. A total of 53 specimens were obtained from research surveys and commercial fisheries, including juveniles and adults ranging in size from 33·5 to 75·6 cm total length (L_T). Estimated size‐at‐maturity was 54·7 cm L_T in males and 64·0 cm L_T in females. Three gravid females (65·0, 67·5 and 71·2 cm L_T) were observed, all with eight embryos. Size‐at‐birth was estimated to be 25–27 cm L_T. Vitellogenesis was not concurrent with embryo development. Analysis of diet from stomach contents, including DNA identification of prey using the mitochondrial genes cox1 and nadh2, revealed that O. bruniensis preys exclusively on the egg capsules of holocephalans, potentially making it the only known elasmobranch with a diet reliant solely upon other chondrichthyans. Based on spatial overlap with deep‐sea fisheries, a highly specialized diet, and reproductive characteristics representative of a low productivity fish, the commercial fisheries by‐catch of O. bruniensis may put this species at relatively high risk of overfishing.     

Investigating trophic‐level variability in Celtic Sea fish predators

The trophic level (T_L) mean and variance, and the degree of omnivory for five Celtic Sea fish predators were estimated using a database of stomach content records characterized by a high level of taxonomic resolution. The predators occupied a high position in the food web, i.e. 4·75 for Atlantic cod Gadus morhua, 4·44 for haddock Melanogrammus aeglefinus, 4·88 for European hake Merluccius merluccius, 5·00 for megrim Lepidorhombus whiffiagonis and 5·27 for whiting Merlangius merlangus. The level of taxonomic resolution of the prey did not greatly affect mean T_L predator values; an effect on variance was evident, low resolution masking intra‐population variability in T_L. Generalized additive models (GAM) were used to explain the variability of predator T_L caused by environmental variables (International Council for the Exploration of the Sea, ICES, division and season) and predator characteristics (total length, L_T). Significant year, location season and interaction effects were found for some species and with L_T at the scale of ICES subdivision. The species‐specific variability of T_L could be due to spatio‐temporal variations in prey availability and in predator selectivity following ontogenetic changes. Omnivorous fish T_L was less affected by spatio‐temporal variations. In addition, results showed that the omnivory index and T_L variability provide dissimilar information on predator feeding strategy. Combining information on T_L variability and omnivory allowed between within‐individual and between‐individual components contributing to trophic niche width to be separated and the type of generalization of fish predators to be identified.     

A rare occurrence of reversal in the common megrim Lepidorhombus whiffiagonis (Pleuronectiformes: Scophthalmidae) in the northern North Sea

An adult (231 mm standard length, L_S; 371 mm total length, L_T), dextral (right‐sided) common megrim Lepidorhombus whiffiagonis is reported from the northern North Sea. This is the first recorded occurrence of reversal in this species. Other than its reversed asymmetry, the specimen had morphological and meristic characteristics similar to those of non‐reversed individuals of the same species.     

Reproductive biology of Haemulon plumierii in the south‐western Atlantic Ocean's most extensive reefs: implications for fisheries management

The reproductive biology of the white grunt Haemulon plumierii was studied from 360 individuals obtained from artisanal fisheries landings in the Abrolhos Bank, Brazil, between August 2010 and March 2012. The overall sex‐ratio did not differ significantly from 1:1, although males predominated in larger size classes. β‐Binomial modelling of historical sex‐ratio data indicated that the catch rate of females has increased in recent years. Females reached maturity at a smaller total length (L_T; 214 mm) than males (235 mm L_T) and the L_T at which 50% of all individuals are mature (L₅₀) was 220 mm, corresponding to 41·5% of the maximum recorded L_T. Variation in the gonado‐somatic index and in the relative frequency of reproductive stages indicates that reproduction occurs year round, with increased activity during the austral spring and summer. Fecundity was not size dependent. The reproductive parameters provided here can support management measures focussed on seasonal closures during spawning peaks (September to November and February to March) and minimum sizes (>L₅₀) for the capture of this important artisanal fisheries resource in Abrolhos, the region with the largest and most biodiverse coralline reefs in the South Atlantic Ocean.     

Reproductive biology and spatiotemporal patterns of spawning in striped marlin Kajikia audax

This study presents the first histology‐based assessment of the reproductive dynamics of south‐west Pacific striped marlin Kajikia audax. Maturity and reproductive status were assessed from histological sections of ovaries (n = 234) and testes (n = 243) of fish caught in commercial longline and recreational fisheries between 2006 and 2009. Spawning peaked in the Coral Sea during November and December at sea surface temperatures between 24·8 and 28·3° C. Lower jaw fork length (L_LJF) at 50% maturity (L_LJF50), a key variable for stock assessment, was estimated to be 2100 ± 102 mm (mean + s.e .) for females and 1668 ± 18 mm for males. Unlike large pelagic tunas Thunnus spp., the proportion of females increased with length and spawning fish formed multiple large‐scale aggregations within a broad latitudinal band. This study provides a starting point for biological parameters needed for stock assessment and conservation of K. audax and introduces the multiple aggregation spawning concept as a reproductive mechanism to explain genetic heterogeneity observed in some highly migratory species.     

Skeletal ontogeny of the vertebral column and of the fins in shi drum Umbrina cirrosa (Teleostei: Perciformes: Sciaenidae), a new candidate species for aquaculture

The osteological development of the vertebral column and fins in shi drum Umbrina cirrosa was studied in order to improve knowledge for its introduction in Mediterranean aquaculture. The osteological development was studied in 171 individuals, of total length (L_T) from 2·7 to 30·2 mm that were reared under the mesocosm technique. Vertebral ontogeny starts at 3·4 and 4·0 mm L_T, with the formation of the first cartilaginous neural and haemal arches, and spines, respectively, and is completed with the full attainment of epicentrals (12·5 mm L_T). The formation of vertebral centra occurs between 4·1 and 7·4 mm L_T. Pectoral supports are the first fin elements to develop (3·0 mm L_T), followed by those of the caudal fin (3·8 mm L_T), pelvic fin (3·9 mm L_T) and finally by those of the dorsal and anal fins (4·5 mm L_T). The caudal fin is the first to develop fin rays and attain the full count of principal fin rays (4·5–6·8 mm L_T), but the last to be fully completed with the formation of procurrent fin rays (6·9–17·5 mm L_T). The next fins starting to present rays are the dorsal (5·3 mm L_T) and the pectoral fins (5·6 mm L_T), while the anal and pelvic fins are the last (5·7 mm L_T). Following the caudal principal fin rays (6·8 mm L_T), the dorsal, anal (6·9 mm L_T), pelvic (7·4 mm L_T) and pectoral fins (9·8 mm L_T) are the next with fully completed ray counts. Aggregation of qualitative changes, such as the appearance of cartilages, the beginning and the complement of the ossification process and the full complement of elements in U. cirrosa were measured as cumulative frequency counts. These measurements reveal three ontogenetic intervals: one very developmentally active period during early life stages (from 3 to 5·9 mm L_T), a second slower developmental period (from 6·0 to 8·9 mm L_T) and finally a period of ontogeny more focused on structure refinement up to metamorphosis and settlement (>9·0 mm L_T).