FEATURES of the REPRODUCTIVE BIOLOGY of the SOUTHERN BLUE WHITING (Micromesistius Australis)*

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Features of the reproductive biology of the southern blue whiting (Micromesistius australis).

Item Type Journal Contribution

Authors Macchi, G.J.; Pájaro, M.

Citation INIDEP documento científico, 5. p. 67-79

Publisher Mar del Plata: Instituto Nacional de Investigación y Desarrollo Pesquero

Download date 28/09/2021 05:14:07

Link to Item http://hdl.handle.net/1834/2566 INIDEP DOC. CIENT., 5: 67-79, 1999 67

FEATURES OF THE REPRODUCTIVE BIOLOGY OF THE SOUTHERN BLUE WHITING (Micromesistius australis)*

GUSTAVO J. MACCHI 1,2 AND MARCELO PÁJARO 1,2

1 National Insitute for Fisheries Research and Development (INIDEP). P.O. Box 175, 7600 - Mar del Plata, Argentina. 2 National Council for Scientific and Technical Research (CONICET).

RESUMEN

Aspectos de la biología reproductiva de la polaca (Micromesistius australis). Se analizan distintos aspectos de la reproducción de la polaca (Micromesistius australis), que incluyen la determinación de la época de puesta, tipo de desove de la especie, estimación de la talla de primera madurez y de la fecundidad. Se trabajó con muestras obtenidas en aguas adyacentes a las Islas Malvinas entre marzo y noviembre de 1995, provenientes de campañas de investigación y del "Programa Nacional de Observadores en Buques Comerciales". Se observó actividad reproductiva de la polaca entre fines de julio y setiembre, al sudoeste de las Islas Malvinas. El análisis microscópico de los ovarios y la dis- tribución de diámetros ovocitarios, permitió establecer que la polaca es un desovante parcial con fecundidad determinada. Esta característica permite estimar la fecundidad anual de la especie me- diante el conteo de ovocitos vitelados en aquellas hembras que se encuentran en estadio de madurez avanzada. Este parámetro fue cercano a los 478.000 ovocitos para una talla media de 51 cm Lt. La talla de primera maduración para las hembras de esta especie fue cercana a los 31 cm Lt.

SUMMARY

Different features of the reproductive biology of the southern blue whiting (Micromesistius australis) are analyzed. Samples were obtained from research cruises and from commercial catches carried out between March-November 1995, in waters near Malvinas Islands. Reproductive activity of M. australis was observed between the end of July and September, southwest of Malvinas Islands. Oocyte diameter distribution of gravid females and the histological observations show that this species is a batch spawner with determinate annual fecundity. Preliminary estimate of the potential annual fecundity was about 478,000 oocytes for a 51-cm mean total length. Size at first maturity for this species was about 31 cm total length.

* INIDEP Contribution Nº 1085. 68 INIDEP DOC. CIENT., 5: 67-79, 1999

Key words: Micromesistius australis, southern blue whiting, Southwest Atlantic, reproduction. Palabras claves: Micromesistius australis, polaca, Atlántico Sudoccidental, reproducción.

and from commercial catches (Argentina’s National INTRODUCTION Scientific Fisheries Observer Programme), carried out between March-November 1995 (Table 1). Micromesistius australis is a mesopelagic The main working area was located southwest species typical of the Cold Malvinas Current. From of Malvinas Islands, but during September other 38°S to 47°S it inhabits waters near to the continen- samples were analyzed, including one taken off the tal shelf at depths ranging from 100 to 700 m; from Malvinas zone, at 47° 20'S - 60° 50'W (Fig. 1). 47°S to 55°S, it distributes over a wider area around Total length (cm) and macroscopical maturity the Malvinas Islands, reaching 800 m depths (Otero, stages were recorder from 1240 females. For this, a 1976; Madirolas, 1996). Southern blue whiting is maturity scale of five stages designed for biological one of the most important resource species in the studies was employed: 1) immature, 2) developing, south Patagonian fisheries. Up to 1982, a signifi- 3) gravid and running, 4) spent and 5) resting cant number of studies on this species were carried (Macchi and Diaz Astarloa, 1996). This classifica- out by Argentine researchers, dealing with biologi- tion was used for the temporal analysis of the rela- cal aspects such as spawning areas and seasons, egg tive composition of maturity stages. and larval morphology and distribution, seasonal For the histological analysis 77 paired ovaries in sexual stages analysis, and length at maturity different maturity stages were selected and fixed in (Weiss, 1974; Ciechomski et al., 1981; Ciechomski 10% formalin. At the laboratory, tissue samples and Booman, 1981; Perrotta, 1982). However, were dehydrated, embedded in paraffin wax and sec- papers dealing with specific aspects on the repro- tioned at 5 µm thickness. The sections were stained ductive biology of this species are scarce: in this with Mayer's haematoxilin and eosin. A microscop- sense, only a paper by Lisovenko et al. (1982), ical maturity scale was established, based on the his- where a preliminary fecundity estimation is made tological analysis of the ovaries. and another by Sánchez et al. (1986) describing the To estimate mean length at first maturity (L50) type of spaw-ning, potential fecundity, length at for females, the fraction of mature fish per 1,0 cm maturity and a preliminary estimation of spawning length intervals was fit to the logistic function. L50 stock can be cited. The goal of the present work is was defined as the length in which 50 % of the indi- to update the existing information on reproductive viduals were mature. Females were considered sexu- aspects of this species concerning type of spawning, ally mature if they were in gonad stage 2 (macro- and reproductive season and area. Moreover, a pre- scopical scale) or higher. liminary estimation of total fecundity was carried A preliminary total fecundity estimation was out. carried out using the gravimetric method (Hunter et al., 1982). For this estimation, 7 ovaries with advanced yolked oocytes were selected. These gonads were weighed and three tissue samples of MATERIAL AND METHODS each paired ovaries were removed from anterior, mid-, and posterior regions. In order to obtain 100- 300 yolked oocytes, tissue samples of 40-100 mg Samples of M. australis were collected during (weighed to the nearest 0.01 mg) were placed on a three research cruises of the INIDEP (Instituto slide, and yolked oocytes counted (Hunter, 1985). Nacional de Investigación y Desarrollo Pesquero) MACCHI AND PÁJARO: REPRODUCTIVE BIOLOGY 69

Table 1. Basic data. Tabla 1. Datos básicos.

Source Ship Origin Month N° n of trawls

OB-04/95 “Capitán Oca Balda” Research vessel March 3 178 CENTURION “Centurión del Atlántico” Commercial fleet July - August 4 412 ROKKO MARU “Rokko Maru” Commercial fleet September 1 25 OB-10/95 “Capitán Oca Balda” Research vessel September 14 263 OB-13/95 “Capitán Oca Balda” Research vessel November 12 253 YAMATO “Yamato” Commercial fleet November 4 109

Figure 1. Map of the study area showing the total sampling stations with occurrence of southern blue whiting. Figura 1. Mapa con la distribución de estaciones en las cuales se obtuvieron muestras de polaca. 70 INIDEP DOC. CIENT., 5: 67-79, 1999

Total fecundity for each female was calculated from classified in a maturity scale of eight stages: the product of the number of yolked oocytes per unit 1 - Immature. This stage is not described weight in the tissue sample and the ovary weight. because the small virginal individuals (< 15 cm TL) were not present in the samples. 2 - Developing (virgin). The microscopical image shows compact ovigerous lamellae, a charac- RESULTS teristic that persists until spawning, and the tunica albuginea is very thin (10-20 µm). Only basophilic oocytes in first growth phase are observed (Fig. 2 A). Ovarian maturation (histological analysis) 3 - Developing (early). A number of oocytes have started the secondary growth phase, and shows The morphological changes observed in the dif- yolk vesicles in the cytoplasm (yolk vesicle stage) ferent oocitary growth phases were similar to those (Fig. 2 B). The larger oocytes, moreover, have yolk established for other species, and the terminology globules between the vesicles (primary yolk stage). used was adapted from Forberg (1982) (Table 2). The remaining oocytes stayed in "resting stage" The main histological changes in the ovary were

Table 2. Morphological changes observed in the different oocitary growth phases. Adapted from Forberg (1982). Tabla 2. Cambios morfológicos observados en las diferentes fases de crecimiento ovocitario. Adaptado de Forberg (1982).

Oocitary growth Description stages

First growth phase Previtellogenic oocytes with diameter smaller than 200 µm. Cytoplasm is Cromatin nucleolus stage basophilic and the nucleus shows a number of nucleoli situated peripherally. Early nucleolus stage Follicular cells are flattened and become visible on the outer surface of oocyte. Late nucleolus stage

Second growth phase Diameter ranged between 200-350 µm. Citoplasm is basophilic and shows small Yolk vesicle stage vacules optically empty (yolk vesicles). Granulosa and follicular theca are distin- guished and the zona radiata become visible around the periphery of oocyte.

Primary yolk stage Diameter ranged between 350-500 µm. Numerous eosinophilic yolk globules appear between the yolk vesicles. These yolk globules are composed mainly of pro- teins. The zona radiata and the follicle epithelium are more prominent.

Secondary yolk stage Diameter between 500-800 µm. The yolk globules have multiplied and increased in size, occupying all the cytoplasm. The nucleus exhibits an irregular shape, and the zona radiata increased in thickness.

Tertiary yolk stage Oocitary diameter ranged between 800-1100 µm. In the first instance, the nucleus is displaced to the animal pole (migratory nucleus stage). The nuclear membrane desintegrates and the yolk globules tend to coalesce. In the section, these oocytes appear with a cytoplasm weakly eosinophilic and an irregular shape. MACCHI AND PÁJARO: REPRODUCTIVE BIOLOGY 71

Figure 2. Ovaries 01'Al. australis at difTerent maturity stages: A) developing (virgin): B) developing (early); C) and D) developing (late). b: previtellogenic oocytes: g: yolk globule; v: yolk vesicle stage; y: yolk globules stage; n: nucleus; z: zona radiata. A), B) and e): bar = 100 J..!m;D): bar = 250 J..!m. Figura 2. Ovarios de M. austra/is en diferentes estadios de madurez: A) juvenil; B) maduración temprana; C) y D) madu- ración avanzada. b: ovocitos previtelogénicos; g: glóbulos de vitelo; v: estadio de vitelo vesicular; y: estadio de vitelo globular: n: núcleo: z; zona radiata. A), B) Y C): segmento = 100 J.lm; D): segmento = 250 J.lm. r

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Temporal variation in the relative centage of gravid females (85 %) was observed (Fig. composition of maturity stage 6). In September the sampled area was larger, and (Macroscopical scale) three zones with different composition of maturity stages were established (Fig. 7): In March, at the southwest of Malvinas, a high A) This is a large area between the southwest of proportion of the resting stage was observed (60%), Malvinas and the northeast of Isla de los Estados. In the rest of the sample consisted of immature indivi- this zone most females were in developing stage duals (Fig. 5). During July-August, the samples (60%). The histological analysis indicates that these were obtained at the northwest of the Burdwood individuals were in early developing phase (stage 3, Bank, near the area sampled during March. In this microscopical scale). The rest of the sample consist- case, a reproductive concentration with a high per- ed of immature individuals.

Figure 5. Map of the study area showing occurrence of southern blue whiting and macroscopical maturity stages during March. Figura 5. Localización de las estaciones realizadas y composición de los estadios de madurez (escala macroscópica), durante marzo. MACCHI AND PÁJARO: REPRODUCTIVE BIOLOGY 75

B) This area ranges from South Malvinas to 4, microscopical scale). the Burdwood Bank, and is located to the east of the During November the samples were obtained previously described area (Fig. 7). In this area, 40% from a large zone between Malvinas, Isla de los of the sample were gravid females, while a high pro- Estados and the Burdwood Bank (Fig. 8). Most portion of spent stage was observed (50%). females were in resting stage (60%), which indicates C) This is one sample far off the Malvinas area the end of the reproductive season. However, a low (Fig. 7). All individuals were in developing stage, percentage (15%) of spawners was observed. and the microscopical analysis established that the oocytes were fully yolked, near to hydration (stage

Figure 6. Map of the study area showing occurrence of southern blue whiting and macroscopical maturity stages during July- August. Figura 6. Localización de las estaciones realizadas y composición de estadios de madurez (escala macroscópica), durante julio - agosto. 76 INIDEP DOC. CIENT., 5: 67-79, 1999

Size at maturity Estimation of total fecundity

Figure 9 shows the percentages of mature females for each length class, between 18.0 - 51.0 Total fecundity was considered to be equivalent to cm TL. Estimated mean length at first maturity the standing stock of yolked oocytes in advanced maturity, prespawning females. The mean value of (L50) was 30.81 cm.

Figure 7. Map of the study area showing different regions (A, B and C) with occurrence of southern blue whiting and macroscopical maturity stages, during September. Figura 7. Localización de las estaciones realizadas en diferentes regiones (A, B y C) y composición de estadios de madurez MACCHI AND PÁJARO: REPRODUCTIVE BIOLOGY 77

total fecundity was 477,771 (206,783 s.d.) oocytes for a 51.1 cm (3,9 s.d.) mean total length fish. DISCUSSION AND CONCLUSIONS Relative fecundity was about 706 (258 s.d.) per gram ovary-free female weight. An eight-stages microscopical ovarian maturity scale was established on the basis of oocyte development phases. The difference with the macroscopical

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meter at 34.69 cm TL and Sánchez et al. (1986) the northern anchovy (Engraulis mordax), (R. obtained a value of 38.0 cm TL. Lasker ed.), U.S. Dep. Commer., NOAA Tech. Finally, the preliminary estimate of the mean Rep. NMFS, Vol. 36, pp. 79-94. total fecundity ranged within the values estimated HUNTER, R.J., MACEWICZ, B.J. LO, N.CH. & by Sánchez et al. (1986). KIMBRELL, C.A. 1992. Fecundity, spawning, and maturity of female Dover sole Microstomus pacificus, with an evaluation of assumptions and precision. Fish. Bull., 90: 101-128. LITERATURE CITED LISOVENKO, L.A., BARABANOV, A.V. & YEFREMENKO, V.N. 1982. (New data on the CIECHOMSKI, J.D. DE & BOOMAN, C.I. 1981. reproduction of the "Southern Putassu", Descripción de embriones y áreas de reproduc- Micromesistius australis (Gadidae) from the ción de los granaderos Macrourus whitsoni y Falkland - Patagonian zoogeographic region). J. Coelorhynchus fasciatus, de la polaca of Ichthyology, 22 (4): 55-67. Micromesistius australis y del bacalao austral MADIROLAS, A. 1996. Acoustic surveys on the Salilota australis en la zona patagónica y southern blue whiting (Micromesistius fueguina del Atlántico Sudoccidental. Physis australis). INIDEP Doc. Cient. 5, this volume. (Bs. As.), Secc. A, 40 (98): 5-14. MACCHI, G.J. & DIAZ ASTARLOA, J.M. 1996. Ciclo CIECHOMSKI, J.D. DE & SANCHEZ, R.P. 1983. reproductivo y fecundidad del lenguado Relationship between ichthyoplankton abun- (Paralichthys patagonicus) Jordan. Rev. Invest. dance and associated zooplankton biomass in Des. Pesq., 10: 73-83. the shelf waters off Argentina. Biol. Ocean., 3 OTERO, H.O. 1976. Contribución al estudio biológi- (1): 77-101. co pesquero de la polaca (Gadidae, CIECHOMSKI, J.D. DE, EHRLICH, M.D., LASTA C.A. & Micromesistius australis Norman, 1937) del SANCHEZ, R.P. 1981. Estudio sobre la distribu- Atlántico Sudoccidental. Physis (Buenos Aires), ción de huevos y larvas de peces en el Mar Secc. A, 35 (91) : 155-168. Epicontinental Argentino y evaluación de los PERROTTA, R.G. 1982. Distribución y estructura efectivos desovantes de anchoíta y merluza. poblacional de la polaca (Micromesistius aus- Contr. Inst. Nac. Des. Pesq., Mar del Plata, 383: tralis). Rev. Invest. Des. Pesq., 3: 35-50. 59-79. SANCHEZ, R.P., CIECHOMSKI, J.D. DE & ACHA, E.M. EHRLICH, M.D., SANCHEZ, R.P., CIECHOMSKI, J.D. 1986. Estudios sobre la reproducción y fecundi- DE, MACHINANDIARENA, L. & PAJARO, M. 1981. dad de la polaca (Micromesistius australis Ichthyoplankton composition, distribution and Norman,1937) en el Mar Argentino. Rev. abundance on the Southern Patagonian shelf Invest. Des. Pesq., 6: 21-43. and adyacent waters. In this volume. HUNTER, R.J., LO, N.C.H. & LEONG, R.J.H. 1985. WEISS, G. 1974. Hallazgo y descripción de larvas de Batch fecundity in multiple spawning fishes. In: polaca (Micromesistius australis) en aguas del An egg production method for estimating sector patagónico (Pisces, Gadidae). Physis spawning biomass of pelagic fish: application to (Buenos Aires), Secc. A., 33 (87): 537-542.