Validated age and growth of the porbeagle shark (Lamna nasus) in the western North Atlantic Ocean

Growth parameters were estimated for porbeagle shark (Lamna nasus) in the northwest Atlantic Ocean on the basis of vertebral annuli. A total of 578 vertebrae was analyzed. Annuli were validated up to an age of 11 years by using vertebrae from recaptured oxytetracycline-injected and known-age sharks. Males and females grew at similar rates until the size of male sexual maturity, after which the relative growth of the males declined. The growth rate of the females declined in a similar manner at the onset of maturity. Growth curves were consistent with those derived from tag-recapture analyses (GROTAG) of 76 recaptured fish and those based on length-frequency methods with measurements from 13,589 individuals. Von Bertalanffy growth curve parameters (combined sexes) were L∞ = 289.4 cm fork length, K = 0.07 and t0 = –6.06. Maximum age, based on vertebral band pair counts, was 25 and 24 years for males and females, respectively. Longevity calculations, however, indicated a maximum age of 45 to 46 years in an unfished population.

Temporal and spatial dynamics of spawning, settlement, and growth of gray snapper (Lutjanus griseus) from the West Florida shelf as determined from otolith microstructures

The goal of our study was to understand the spatial and temporal variation in spawning and settlement of gray snapper (Lutjanus griseus) along the West Florida shelf (WFS). Juvenile gray snapper were collected over two consecutive years from seagrass meadows with a benthic scrape and otter trawl. Spawning, settlement, and growth patterns were compared across three sampling regions (Panhandle, Big bend, and Southwest) by using otolith microstructure. Histology of adult gonads was also used for an independent estimate of spawning time. Daily growth increments were visible in the lapilli of snapper 11–150 mm standard length; ages ranged from 38 to 229 days and estimated average planktonic larval duration was 25 days. Estimated growth rates ranged from 0.60 to 1.02 mm/d and did not differ among the three sampling regions, but did differ across sampling years. Back-calculated fertilization dates from otoliths indicated that juveniles in the Panhandle and Big Bend were mainly summer spawned fish, whereas Southwest juveniles had winter and summer fertilization dates. Settlement occurred during summer both years and in the winter of 1997 for the southern portion of the WFS. Moon phase did not appear to be strongly correlated with fertilization or settlement. Histological samples of gonads from adults collected near the juvenile sampling areas indicated a summer spawning period.

Seasonal growth of King George whiting (Sillaginodes punctata) estimated from length-at-age samples of the legal-size harvest

Samples of 11,000 King George whiting (Sillaginodes punctata) from the South Australian commercial and recreational catch, supplemented by research samples, were aged from otoliths. Samples were analyzed from three coastal regions and by sex. Most sampling was undertaken at fish processing plants, from which only fish longer than the legal minimum length were obtained. A left-truncated normal distribution of lengths at monthly age was therefore employed as model likelihood. Mean length-at-monthly-age was described by a generalized von Bertalanffy formula with sinusoidal seasonality. Likelihood standard deviation was modeled to vary allometrically with mean length. A range of related formulas (with 6 to 8 parameters) for seasonal mean length at age were compared. In addition to likelihood ratio tests of relative fit, model selection criteria were a minimum occurrence of high uncertainties (>20% SE), of high correlations (>0.9, >0.95, and >0.99) and of parameter estimates at their biological limits, and we sought a model with a minimum number of parameters. A generalized von Bertalanffy formula with t0 fixed at 0 was chosen. The truncated likelihood alleviated the overestimation bias of mean length at age that would otherwise accrue from catch samples being restricted to legal sizes.

Effect of sodium bicarbonate on hatching and on postembryonic growth of Brachydanio rerio, Cyprinus carpio, Labeo rohita, Cirrhinus mrigala and Catla catla

The treatment of sodium bicarbonate at the dosage of 100 to 1000 mg/litre has been tested experimentally on the hatching and postembryonic growth of Brachydanio rerio, Cyprinus carpio, Labeo rohita, Cirrhinus mrigala and Catla catla. Lower dosages of 100 to 200 mg have been found to reduce the hatching period, yolk absorption period and improve the survival and growth of the post embryonic larvae. The higher dosages of 500 to 1000 mg has been found to reduce the hatching percentage and post embryonic growth of the larvae. The findings indicate that application of sodium bicarbonate in the hatchery and nursery management of carps in the lower dosages of 100 to 200 mg/L to improve hatching and postembryonic growth.

Some key concepts in fisheries research and management, with emphasis on Mozambique

Some basic concepts of fishery economics and management, and fish population dynamics are recalled, as presented during a course held at the Instituto de Investigaçāo Pesqueira from 23 February to 15 March 1988 in Maputo, Mozambique. Also, some basic elements of length-based stock assessment are reviewed, with emphasis on their implementation through the “Compleat Elefan" package, used extensively during this course, when the participants analyzed their data and wrote first draft of manuscripts incorporating the results of these analyses. Some problems relative to sampling and to seasonal growth oscillations are discussed with special reference to conditions in Mozambique.

Status of fish broodstock management and seed production in Bangladesh

The study was conducted with the broad objectives to assess the existing situation of broodstock management and fish seed production in private fish seed farms in Bangladesh. The data were collected from 100 private hatcheries and 40 nurseries in seven upazilas under four districts. There was no shed in forty hatcheries and the owners faced many problems. Brood fish ponds were found suitable for rearing brood fish. About 66% of the hatchery owners collected brood fish from their own ponds and ponds of neighboring areas. Activities like pond preparation; manuring and supplementary feeding were done properly but stocking density of brood fish in 76% of the hatcheries was 3,000-7,000 kg/ha. Infection of argulosis was found in brood fish of 87% of the hatcheries. About 67% of the hatchery owners practiced inter-species crossing. Major problems faced by the hatchery owners were argulosis of brood fish, unavailability of pure brood stock, inadequate brood fish pond. The hatchery owners were found interested to find out the preventive measures of argulosis, develop pure brood stock of indigenous carp and import pure strain of exotic carp. According to the nursery operators, they cultivated hybrid fry because of high demand, rapid growth and good taste. Problems of using hatchery spawn as mentioned by the nursery operators were inbreeding, under sized and aged brood stock, stunted growth, physical deformities and high mortality of spawn due to unknown causes.

Nursery management system of stinging catfish, Heteropneustes fossilis and walking catfish, Clarias batrachus in Bangladesh

A total of four experiments were conducted to develop nursery management system for the two important native catfishes viz. stinging catfish, Heteropneustes fossilis and walking catfish, Clarias batrachus during 2003 and 2004. Two experiments were conducted in on-station condition to determine stocking density efficacy in hapa and in earthen mini ponds for H. fossilis. This was followed by on-farm trial on stocking density in earthen mini ponds. In hapa, the highest survival rate was 60% for H. fosssilis at stocking density of 100/square meter; followed by 54.5 and 50% at stocking densities of 150 and 200/square meter, respectively. Similarly, gain in weight and length was also better in lower stocking densities. Similar survival rate (45 to 55%) was observed in three densities in earthen mini ponds. However, gain in weight and length showed no significant (p<0.05) differences. H. fossilis, C. batrachus showed almost similar survival rates (57.5-59.0%) in all the three stocking densities (100, 150 and 200/square meter) in earthen mini ponds in on-station condition. In terms of gain in weight and length showed no significant (p<0.05) differences in pond conditions. Almost similar result was obtained in terms of growth and survival in on-farm condition.

Management of euglenophytes in aquaculture ponds for improvement of fish production

Four experiments each with three replications were conducted in 12 experimental ponds to control the euglenophytes bloom viz. treatment 1 (T1, covering of one third of the water surface by duckweed (Lemna minor); treatment 2 (T2), application of 123.5 kg lime/ha/month; treatment 3 (T3), use of both duckweed as in T1 and lime as in T2; treatment 4 (T4) was considered as control where neither duckweed nor lime was applied. Fishes comprising of rohu (Labeo rohita), catla (Catla catla), mrigal ( Cirrhinus cirrhosus), silver carp (Hypophthalmichthys molitrix) and silver barb (Barbonymus gonionotus) were stocked at the rate of 1080 fishes/ha with the species ratio of 8:4:6:9:13, respectively. The lowest cell density of euglenophytes was found in the ponds of T3 followed by T2, and T1. In the ponds of T3, euglenophytes bloom did not occur possibly due to alkaline pH, shade and nutrient absorption by duckweed. Thin bloom was observed in the ponds of T1 where pH was neutral or slightly alkaline. The grazing on euglenophytes by the silver carp and silver barb also had some contribution in controlling the bloom. Growth of fishes was comparatively higher in the ponds of T3 and T1, which might be due to better water quality and availability of adequate food while the lower fish growth as recorded from the ponds of T4 might be due to euglenophytes bloom. Thick bloom inhibited light penetration which hampered photosynthesis and growth of other phytoplankton that are the preferred food of planktivorous fishes. Mortality of fishes in ponds having euglenophytes bloom was possibly due to formation of anoxic situation in the early morning or due to the combined effect of anoxic situation and toxic metabolites secretion by the euglenophytes.

Survival, growth and production of Penaeus monodon and P. indicus at different density combinations with milkfish

Penaeus monodon and P. indicus juveniles were stocked and reared for about 3 months in earthen ponds at different density combinations with Chanos chanos. The presence of either Penaeus species at any density ratio did not affect significantly the C. chanos survival. Survival rates of the penaeids indicated that intraspecific and interspecific competition occurred and were reduced with the reduction in stocking rate. It is concluded that further studies on higher density ratios and feeding and economic consideration would be of help to the development of this kind of fishpond management system.

Population dynamics and management of yellowfin tuna (Thunnus albacares) of the Oman Sea

The Yellowfin tuna was caught more than all other species in the southern waters of Iran (24000 tons in 1998). In order to come up with the responsible fishing pattern, there was a need to identify some of the biological characteristics and population dynamic parameters. This thesis was the first which covered the whole Yellowfin tuna distribution in the Oman Sea, included the fishing grounds of Berris, Ramin, Chabahar, Pozm and Jask. The data during 1998-99 from different fishing grounds were polled. Based on the exponential relationship between length and weight in the size range 38-173 Cm, the relationship (W=aL^ b) was calculated as W=0.000012L ^ 3.0831). The mean fork length,head length,girth and weight were calculated respectively 84.15 Cm, 23 Cm, 53 Cm, and 11828 g. Length infinity was estimated 189 Cm with growth parameters of 0.42 per year. Growth performance index was 4.18 which was in agreement with the findngs of the other studies in the Indian and Pacific Oceans. The mortality parameters and exploitation rate were estimated as below: Z = 1.75-1.85 M=0.6 F=1.25 E=0.68 Occurence of empty stomach was high (60%) in the speciemens obtained from the Oman Sea. Purpleback flying squid (Sthenoteuthis oualaniensis) was the most dominant prey species observed in the study (57% in females and 60% in males), occurrence of teleost fishes were found to be the second (38% in males and 42% in females). Crabs also were identified in the specimens(1-2%). The study on sex ratio indicated that males were predominant at all sizes above 120 Cm fork length. 50.82% of specimens were males and 49.18% females. The monthly gonadosomatic index was deriven higher values during January to June which could be indicated as spawning period.