Fish recolonization in temperate Australian rockpools: a quantitative experimental approach

Understanding recolonization processes of intertidal fish assemblages is integral for predicting the consequences of significant natural or anthropogenic impacts on the intertidal zone. Recolonization of experimentally defaunated intertidal rockpools by fishes at Bass Point, New South Wales (NSW), Australia, was assessed quantitatively by using one long-term and two short-term studies. Rockpools of similar size and position at four sites within the intertidal zone were repeatedly defaunated of their fish fauna after one week, one month, and three months during two shortterm studies in spring and autumn (5 months each), and every six months for the long-term study (12 months). Fish assemblages were highly resilient to experimental perturbations—recolonizing to initial fish assemblage structure within 1−3 months. This recolonization was primarily due to subadults (30−40 mm TL) and adults (>40 mm TL) moving in from adjacent rockpools and presumably to abundant species competing for access to vacant habitat. The main recolonizers were those species found in highest numbers in initial samples, such as Bathygobius cocosensis, Enneapterygius rufopileus, and Girella elevata. Defaunation did not affect the size composition of fishes, except during autumn and winter when juveniles (<30 mm TL) recruited to rockpools. It appears that Bass Point rockpool fish assemblages are largely controlled by postrecruitment density-dependent mechanisms that indicate that recolonization may be driven by deterministic mechanisms.

Quantitative determination of the timing of otolith ring formation from marginal increments in four marine teleost species from northwestern Australia

The sectioned otoliths of four fish species from a tropical demersal trawl fishery in Western Australia revealed a series of alternating trans-lucent and opaque zones in reflected light. The translucent zones, referred to as growth rings, were counted to determine fish ages. The width of the opaque zone on the periphery of the otolith section as a proportion of the width of the previous opaque zone (index of completion) was used to determine the periodicity of growth-ring formation. This article describes a method for modeling changes in the index of ring completion over time, from which a parameter for the most probable time of growth-ring formation (with confidence intervals) can be determined. The parameter estimate for the timing of new growth-ring formation for Lethrinus sp. 3 was from mid July to mid September, for Lutjanus vitta from early July to the end of August, for Nemipterus furcosus from mid July to late September, and for Lutjanus sebae from mid July to mid November. The confidence intervals for the timing of formation of growth rings was variable between species, being smallest for L. vitta, and variable between fish of the same species with different numbers of growth rings. The stock assessments of these commercially important species relies on aging information for all the age classes used in the assessment. This study demonstrated that growth rings on sectioned otoliths were laid down annually, irrespective of the number of growth rings, and also demonstrated that the timing of ring formation for these tropical species can be determined quantitatively (with confidence intervals.

An evaluation of back-calculation methodology using simulated otolith data

I simulated somatic growth and accompanying otolith growth using an individual-based bioenergetics model in order to examine the performance of several back-calculation methods. Four shapes of otolith radius-total length relations (OR-TL) were simulated. Ten different back-calculation equations, two different regression models of radius length, and two schemes of annulus selection were examined for a total of 20 different methods to estimate size at age from simulated data sets of length and annulus measurements. The accuracy of each of the twenty methods was evaluated by comparing the back-calculated length-at-age and the true length-at-age. The best back-calculation technique was directly related to how well the OR-TL model fitted. When the OR-TL was sigmoid shaped and all annuli were used, employing a least squares linear regression coupled with a log-transformed Lee back-calculation equation (y-intercept corrected) resulted in the least error; when only the last annulus was used, employing a direct proportionality back-calculation equation resulted in the least error. When the OR-TL was linear, employing a functional regression coupled with the Lee back-calculation equation resulted in the least error when all annuli were used, and also when only the last annulus was used. If the OR-TL was exponentially shaped, direct substitution into the fitted quadratic equation resulted in the least error when all annuli were used, and when only the last annulus was used. Finally, an asymptotically shaped OR-TL was best modeled by the individually corrected Weibull cumulative distribution function when all annuli were used, and when only the last annulus was used.

Quantitative and qualitative studies on the bacterial flora of fresh sardines

Plate counts at R T and 8 C on the skin with muscle and the gut contents of absolutely fresh sardines (Sardinella longiceps) caught off Cochin showed a seasonal variation when sampling was done over a period of 12 months. The counts of the gut contents ran parallel with those of the skin with muscle, but at a higher level of magnitude. Qualitatively, the analysis of 360 strains of bacteria isolated from the skin with muscle and 100 strains from the guts during a year's study revealed a very high preponderance of Gram negative rods, mainly of Achromobacter, Vibrio, and Pseudomonas groups. The percentage of Gram positive organism was very low or nil at times in the ocean fresh sardines.

Quantitative survey of Sargassum along the south-west coast of Ceylon

Sargassum is a brown seaweed from which alginic acid is extracted. A survey was carried out off the south-west coast of Ceylon in December 1963 and January 1964 with the view to determining the quantity of Sargassum available.

Some considerations on methodology for catch assessment in Lake Niassa (Mozambique)

Lake Niassa fisheries are artisanal and are carried out by numerous fishing boats using various types of gear and operating from numerous fish landing places scattered along the shoreline. A frame survey was conducted in 1983 to get information on the size and structure of the fisheries in Lake Niassa. The methodology to be applied for a catch assessment survey is explained. The primary objective of the survey is to obtain reliable current estimates, for the Mozambican side of Lake Niassa, of the total quantity of fish harvested by the fishermen at the lake (in terms of live weight in tons). Secondary objectives include the species composition of the catch and the fishing effort involved in obtaining the catch.

Quantitative and qualitative assessment of plankton: some ecological aspect and water quality parameters of the river Meghna, Bangladesh

Investigation on the seasonal distribution and abundance of various major taxa of phyto and zooplankton and the corresponding physico-chemical characteristics were carried out in four selected stations between the latitude 22°35.494N N-23°23.987 N and longitude 90°35.793 E- 90°49.061 E of the Meghna river system, Bangladesh. Drop count method was followed for the qualitative and quantitative analysis of both phyto- and zooplankton. A total of 41 phytoplankton genera belonging to 17 families and 13 zooplankton genera belonging to 11 families were recorded. Zooplankton growth cycle was noticeably less (3.0%) than the phytoplankton abundance almost throughout the study period. Quantity of plankton registered to increase chronologically from the upper to lower stretches of the river. During summer investigation the load of phytoplankton was recorded maximum (11,300-51,850 No/1). Ratio-wise quantitative difference between zoo- and phytoplankton in composition of the total standing crop fluctuated between 1.0:5.5 and 1:1037. Among the phytoplanktonic groups, Chlorophyceae was found to be dominating (95.0%) in all sampling stations. Protococcus, a single genus of Chlorophyceae played a unique role during summer, contributing the highest density of about 74.0%. The pattern of qualitative and quantitative difference of plankton standing crop in different sampling sites can be attributed to the existing physico-chemical characteristics, mainly water temperature, pH and hardness.

The bacteriology of oil sardine (Sardinella longiceps) and mackerel (Rastrelliger kanagurta) caught from tropical waters off Cochin. 1 - Quantitative aspects

The total aerobic viable plate counts (TPCs) of skin, gills and intestine of newly caught oil sardine (Sardinella longiceps) and Indian mackerel ( Rastrelliger kanagurta) at four different temperatures, namely 36 ± 1°C, 28 ± 2°C (RT), 8 ± 1°C and 1 ±1°C, are reported. The total plate count at RT of the skin of oil sardine and Indian mackerel were in the range of l0 super(3) to 10 super(7) and 10 super(4) to 10 super(6) per cm², that of gills in the range of 10 super(5) to 10 super(9) and 10 super(4) to 10 super(8) per g and that intestine in the range of 10 super(5) to 10 sueper(9) and 10 super(5) to 10 super(8) per g respectively. The TPCs were markedly affected by the incubation temperature. Incubation at 28 ± 2°C gave the highest count; at 36 ± 1°C and 8 ± 1°C, the counts decreased by nearly 1-2 log cycles from that at RT. Incubation at 1 ± 1°C registered the lowest count. The peak values for bacterial counts of these fishes occurred at different periods of the year.

Exploring Indonesian aquaculture futures

Aquaculture is the fastest-growing food production sector globally, with production projected to double within the next 15–20 years. Future growth of aquaculture is essential to providing sustainable supplies of fish in national, regional and global fish food systems; creating jobs; and maintaining fish at affordable levels for resource-poor consumers. To ensure that the anticipated growth of aquaculture remains both economically and ecologically sustainable, we need to better understand the likely patterns of growth, as well as the opportunities and challenges, that these trends present. This knowledge will enable us to better prioritize investments that will help ensure the sustainable development of the sector. In Indonesia, WorldFish and partners have applied a unique methodology to evaluate growth trajectories for aquaculture under various scenarios, as well as the opportunities and challenges these represent. Indonesia is currently the fourth largest aquaculture producer globally, and the sector needs to grow to meet future fish demand. The study overlapped economic and environmental models with quantitative and participatory approaches to understand the future of aquaculture in Indonesia. Such analyses, while not definitive, have provided new understanding of the future supply and demand for seafood in Indonesia stretching to 2030. The learning from this research provides a foundation for future interventions in Indonesian fish food systems, as well as a suite of methodologies that can be applied more widely for insightful analyses of aquaculture growth trajectories in other countries or regions.

A quantitative study of Vibrio parahaemolyticus (Sakazaki et al) in Etroplus suratensis (Bloch) and Metapenaeus dobsoni (Miers) from Cochin backwater

Seasonal variation of Vibrio parahaemolyticus in fish (Etroplus sauratensis) and prawn (Metapenaeus dobsoni) was monitored from March 1982 to February 1983. Analyses of total viable count, vibrio-like organisms, V. parahaemolyticus like organisms and V. parahaemolyticus showed that they occur more in prawn than in fish. In a more polluted environment, the counts of V. parahaemolyticus associated with fish were found to be higher than in prawn.

Selection and application of a suitable sampling method for quantitative and qualitative evaluation of lab-lab

Milkfish and prawn pond operation in the Philippines is often associated with lab-lab culture. Lab-lab is a biological complex of blue-green algae, diatoms, bacteria and various animals which form a mat at the bottom of nursery ponds or floating patches along the margins of ponds. This complex is considered the most favorable food of milkfish in brackishwater ponds. Variations in the quantity and quality of lab-lab between and within areas of a 1,000 sq. m. pond was determined over 2 culture periods (6 month duration) and the applicability and suitability of stratified random sampling as a method of sampling lab-lab was evaluated.

Methodology for valuing wetlands in Uganda

The wetlands in Uganda are undergoing rapid degradation. Swamps provide a habitat for birds, fishes and other animals. They have many ecological functions and, furthermore, supply people with multiple resources, such as reeds, herbs, fish and agricultural products. Although some'uses of wetland are sustainable, others lead to rapid deterioration. The main threat to swamps are human activities. One reason for the progressive destruction of wetlands is that the people may not appreciate the existence of and the treasures represented by wetlands even if they live in arm long distance from them. Another reason is that the two most important user groups of wetlands, farmers and fishermen, although having conflicting interests concerning the wetlands, hardly interact. A study, done as part of the Ecotone Project at the Fisheries Research Institute (FIRI), tries to evaluate in monetary terms how much Uganda loses with progressive destruction of wetlands. The study looks first at which uses of the wetlands are of importance and thereafter it examines, what data is needed and available to calculate the values of those uses.