Do fluctuations in the somatic growth rate of rock lobster (Jasus lalandii) encompass all size classes? A re-assessment of juvenile growth

Catch rates in the South African rock lobster (Jasus lalandii) fishery declined after 1989 in response to reduced adult somatic growth rates and a consequent reduction in recruitment to the fishable population. Although spatial and temporal trends in adult growth are well described, little is known about how juvenile growth rates have been affected. In our study, growth rates of juvenile rock lobster on Cape Town harbor wall were compared with those recorded at the same site more than 25 years prior to our study, and with those on a nearby natural nursery reef. We found that indices of somatic growth measured during 1996–97 at the harbor wall had declined significantly since 1971–72. Furthermore, growth was slower among juvenile J. lalandii at the harbor wall than those at the natural nursery reef. These results suggest that growth rates of juvenile and adult J. lalandii exhibit similar types of spatiotemporal patterns. Thus, the recent coastwide decline in adult somatic growth rates might also encompass smaller size classes.

Effect of high and low cost brood feeds on gonado-somatic index and fecundity of freshwater prawn Macrobrachium rogenbergii de Man

Studies were conducted to observe the effects of different types of feeds on the gonado-somatic index (GSI) and fecundity of freshwater prawn Macrobrachium rogenbergii. Three different treatments (T1 T2 and T3) were designed with three types of feed as follows: (i) Saudi-Bangla Prawn feed 100% - T1 (ii) SaudiBangla prawn feed 50%+ local feed 50%- T2 and (iii) local feed 100%- T3. The results showed that the average value of gonado-somatic index (GSI) was 14.39, 14.35 and 14.36 and the average fecundity of M. rogenbergiiwas 99,741, 98,125 and 97,911 in T1 T2 and T3 respectively. No significant difference (p>00.5) was between gonado-somatic indices (GSI) and fecundities of M. rogenbergii among different feeding trails. The price of Saudi-Bangla prawn feed was very high (Tk. 23/kg) than the local feed (Tk. 14/kg). So, use of local feed was recommended for M. rogenbergii brood rearing.

A comparative study on the embryonic development of gynogen, triploid, haploid and normal diploid embryos of stinging catfish, Heteropneustes fossilis

UV irradiation and cold shock were applied on the eggs of stinging catfish, Heteropneustes fossilis, to produce haploid,. gynogen and triploid embryos. A comparative account of the various features· of embryonic development in chromosomally manipulated groups viz. haploid, gynogen and triploid and non-manipulated normal diploid group of H fossilis has been discussed. A slow development and delayed hatching were observed in gynogen and triploid embryos compared to those in normal diploid (control) groups. Mass mortality was observed in all chromosomally manipulated groups particularly during the gastrulation stage. The hatchlings of the gynogen, triploid and normal diploid were similar in overall appearance.