Physiological ecology of juvenile chinook salmon (Oncorhynchus tshawytscha) at the southern end of their distribution, the San Francisco Estuary and Gulf of the Farallones, California

Juvenile chinook salmon, Oncorhynchus tshawytscha, from natal streams in California’s Central Valley demonstrated little estuarine dependency but grew rapidly once in coastal waters. We collected juvenile chinook salmon at locations spanning the San Francisco Estuary from the western side of the freshwater delta—at the confluence of the Sacramento and San Joaquin Rivers—to the estuary exit at the Golden Gate and in the coastal waters of the Gulf of the Farallones. Juveniles spent about 40 d migrating through the estuary at an estimated rate of 1.6 km/d or faster during their migration season (May and June 1997) toward the ocean. Mean growth in length (0.18 mm/d) and weight (0.02 g/d) was insignificant in young chinook salmon while in the estuary, but estimated daily growth of 0.6 mm/d and 0.5 g/d in the ocean was rapid (P≤0.001). Condition (K factor) declined in the estuary, but improved markedly in ocean fish. Total body protein, total lipid, triacylglycerols (TAG), polar lipids, cholesterol, and nonesterified fatty acids concentrations did not change in juveniles in the estuary, but total lipid and TAG were depleted in ocean juveniles. As young chinook migrated from freshwater to the ocean, their prey changed progressively in importance from invertebrates to fish larvae. Once in coastal waters, juvenile salmon appear to employ a strategy of rapid growth at the expense of energy reserves to increase survival potential. In 1997, environmental conditions did not impede development: freshwater discharge was above average and water temperatures were only slightly elevated, within the species’ tolerance. Data suggest that chinook salmon from California’s Central Valley have evolved a strong ecological propensity for a ocean-type life history. But unlike populations in the Pacific Northwest, they show little estuarine dependency and proceed to the ocean to benefit from the upwelling-driven, biologically productive coastal waters.

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.

Biology and morphometry study of Drepane punctata (Cuv and Val) at juvenile stage of Bombay coast

The metric and meristic characters of Drepane punctata from Versova Fish Landing Centre of Bombay have been studied. The meristic characters showed considerable variations. The number of dorsal fin rays were relatively stable characters. Statistical interpretation of metric data indicated that there is a direct relationship between the preanal, predorsal in relation to total length and eye-diameter in relation to head length.

Length-weight relationship of Drepane punctata (Cuv. & Val.) at juvenile stage off Bombay coast

The study of the length weight relationship is highly useful to the fishery biologists in the study of population dynamics of fish and for determining the pattern of growth of stock. The parabolic equation for the length-weight relationship of Drepane punctata juveniles off the Bombay coast, expresses the value of "n" 2.83, indicating that the growth rate is less than the cube length.

Gill pathology of juvenile carps in nursery ponds

Gill pathology of juveniles of two Indian major carps Labeo rohita and Cirrhinus mrigala were studied for a culture period of three months in a private and a government fish farm pond. Under histopathological observations, only protozoan parasite, Myxobolus sp., was recorded as cyst. These myxosporidian cysts were high in the gills of L. rohita of the government farm pond followed by C. mrigala of the private farm pond. Hypertrophic gill lamellae (primary and secondary) with loss of secondary lamellae were evidenced in C. mrigala of privately operated pond.

Some aspects of population dynamics of juvenile hilsa shad (Tenualosa ilisha Ham.) from the Meghna river, Bangladesh

Population dynamics of the juvenile hilsa shad (Tenualosa ilisha) in the nursery ground of the Meghna River have been studied on the basis of the length cohort analysis of 8023 specimens. The growth parameters viz; asymptotic length (Lα), curvature character (K) and initial time (t0) were found to be 30.69 cm, 1.2 yrˉ¹ and 0.45 yrˉ¹ respectively. Curvature parameter indicates that jatka is a fast growth performer. The natural, fishing and total mortality were found to be 1.37 yrˉ¹, 1.41 yrˉ¹ and 2.78 yrˉ¹ respectively. Survival rate (S) was found to be 6.2%. A small difference was found between the age at first capture (Tc) and the recruitment age (Tr). Stocks of jatka seem to be overexploited and need to be conserved.

Studies on the effect of compounded feeds on the growth of juvenile Banana prawn Penaeus merguiensis

Laboratory experiments were conducted to determine the effect of compounded feeds on growth of juveniles (3 to 4 cm) of the Banana prawn Penaeus merguiensis. In all, seven diets were prepared with different combinations of locally available ingredients. Diascure, a local tuber was used as source of carbohydrate and vitamin mineral mixture (1%) was used in all the diets. The results indicated that diets with groundnut cake (diet 2, 3, 5 and 7) produced better survival and growth. In diets 4 and 6 growth was good but survival was very poor. Amongst all the diets, diet 7 produced significantly better growth, survival and food conversion ratio.

Estimation of fishing mortality and migration coefficient of the fishery of juvenile Macrobrachium rosenbergii from Kalu River in Maharashtra

The freshwater prawn, Macrobrachium rosenbergii breeds in estuaries and the juveniles after completion of their larval stage start their upward migration towards rivers. It is at this stage fishing of juveniles takes place in river mouths. Kalu River near Titwala, in Maharashtra is estimated based on data presented by Indulkar and Shirgur (1995) for 1991 and 1992 fishing seasons. The fishing mortality was estimated to be 1.50 and 1.28 for a fishing season of 3 months in 1991 and 1992 respectively, while the migration coefficient was computed to be 3.53 during the fishing season. As the average exploitation rate during the study period was only 0.24, the juveniles are not heavily fished and there is a scope for almost doubling the present catch to about 4 million seeds per fishing season.

A CMOS analogue predistortion circuit for wideband optical fibre links

The laser is a major source of nonlinearity for optical fibre communication systems. In this paper, we propose a CMOS analogue predistortion circuit to reduce laser nonlinearity for wideband optical fibre links. The circuit uses a nonlinearity having the inverse transfer characteristic of the directly modulated vertical cavity surface emitting laser (VCSEL). It is shown by post-layout simulation that the predistortion circuit shows 12dBm improvement in the optical fibre system. The optical fibre transmitter front-end with predistortion lineariser is being fabricated using the austriamicrosystems (AMS) 0.3 5μm CMOS technology.