POPULATION STRUCTURE AND GONADAL MATURATION IN SEA URCHINS AND SEA CUCUMBERS FOUND ON THE ROCKY COAST OF KARACHI, PAKISTAN

Saima Siddique, . (2015) POPULATION STRUCTURE AND GONADAL MATURATION IN SEA URCHINS AND SEA CUCUMBERS FOUND ON THE ROCKY COAST OF KARACHI, PAKISTAN. Doctoral thesis, University of Karachi, Karachi.

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Abstract

Although several species of sea cucumber and sea urchin were reported but the population biology of none of these species are known from Pakistan. In the present study population structure and reproductive pattern of sea cucumber, Holothuria arenicola were studied on rocky shores of Buleji and Manora, Karachi. The population structure and reproductive pattern of sea urchin, Echinometra mathaei were studied on Buleji only as it was absent on Manora. The study was conducted during the period April 2011 to November 2012. Size of Holothuria arenicola population in the present study differed at Manora and Buleji with a mean length of 141.2 ± 75.9 and 115.7 ± 34.9 mm, respectively. Mean adult weight also differed being higher at Manora (51.0 ± 64.8 g) than at Buleji (23.9 ± 25.5 g). All measured biometric characters, that is, body length, width, wet weight and gutted weight in H. arenicola showed significant temporal variations and width/length, wet weight/length, gutted weight/length and gutted weight/wet weight relationships followed negative allometry indicating a change in body shape as the animal grows at both sites. Length frequency distribution analysis was bimodal in both summers and autumns consisting of small-sized and medium-sized individual while in winter and spring three modes were found at Manora. While at Buleji, the population was unimodal in all seasons consisting of small-sized individuals. The theoretical growth parameters, K, and L? calculated for H. arenicola by applying von Bertalanffy growth equation were 0.37 yr-1 and 40.9 cm, respectively at Manora and 0.48 yr-1 and 38.9 cm, respectively at Buleji. The longevity (tmax) in this species was found to be 8.1 years at Manora and 6.3 years at Buleji. The natural mortality coefficient (M) was 0.853 year-1 at Manora and 1.026 year-1 at Buleji. Sex in H. arenicola cannot be determined externally but can be identified on examination of gonad colour which is orangish in females and creamish yellow in males. The reproductive cycle of the population of H. arenicola in coastal waters of Karachi was analysed from April 2011 to November 2012 by histological examination of gonad. Five gonadal stages were described: undetermined, early developing, late developing, mature and partially spawned stages. The distinguishing features used to describe gonad stages in both sexes included the main features of reproductive cells and gonad wall. The sex ratio in H. arenicola was approximately 1:1 and in nearly 50% of individuals the sex (including with and without gonad) could not be determined. The gonad index (GI) for both males and females showed a similar gonadal cycle as an increased GI values were observed from April to September and decreased values from October to February. The reproductive cycle based on histological staging of gonads showed a clear annual pattern and was synchronous in both males and females. Spawning occurred during the spring-summer season (April to September), followed by resting phase in autumn and winter (October to February). The spawning showed a significant negative correlation with salinity, significant positive correlation with chlorophyll-a and a non-significant correlation with temperature. Due to roughness of sea sampling was not possible during June to August period in years 2011 and 2012, the study of Echinometra mathaei is based on 14 months instead of 20 months. All measured biometric characters, that is, that is, test diameter, test height and wet weight in sea urchin E. showed significant temporal variations. The mean test diameter of 46.6 ± 6.3 mm and mean weight of 50.1 ± 18.3 g was found in this species at Buleji. The wet weight/test diameter relationships followed negative allometry and the test height/test diameter relationship was isometric. Length frequency distribution analysis was mostly bimodal consisting of medium-sized and large-sized individuals of E. mathaei. Comparison of the growth of various cohorts showed that sea urchins grow at faster rate in winter than summer. The theoretical growth parameters, K, and L? calculated for E. mathaei. By applying von Bertalanffy growth equation was 0.48 yr-1 and 8.2 cm, respectively. The longevity (tmax) was found to be 5.7 years and natural mortality was 1.584 year-1. Sex in E. mathaei cannot be determined externally but can be identified on examination of gonad colour which is dark yellow in females and light yellow in males. The sex was further confirmed on histological examination and maturation was divided into five stages, that is, immature/resting, premature, mature, partially spawned and spent. The over-all sex-ratios in the population of E. mathaei did not follow the Mendelian 1:1 ratio and was significantly in favour of females. The gonad index (GI) for both males and females showed a similar gonadal cycle as an increased GI values were observed from April to September and decreased values from October to February. There was a slight increase in the gonad weight with the increase in the body weight in males and females of E. mathaei, but this relationship was not significant statistically. The relationships between body weight/gonad weight and body weight/GI were non-significant in males and females of E. mathaei. The reproductive cycle in this species was approximately synchronous for both males and females. Based on histological staging of gonad, spawning was observed during autumn and winter, followed by no spawning in spring and early summer (as no data available for mid- summer). The spawning showed a weak correlation with seawater temperature, salinity and chlorophyll-a.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: POPULATION,GONADAL,MATURATION,URCHINS,CUCUMBERS,ROCKY,COAST
Subjects: Q Science > QD Chemistry
Depositing User: Ms Maryam Saeed
Date Deposited: 26 Oct 2017 06:52
Last Modified: 26 Oct 2017 06:52
URI: http://eprints.hec.gov.pk/id/eprint/6843

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