Age and growth of yellowtail snapper and queen triggerfish collected from the U.S. Virgin Islands and Puerto Rico

Opaque rings on sectioned otoliths and sectioned dorsal spines were used to age yellowtail snapper, Ocyurus chrysurus (N = 654) and queen triggerfish, Balistes vetula (N = 665), taken from U.S Virgin Islands and Puerto Rico trap and hook-and-line fisheries in 1983 and 1984. Annulus formation, validated by marginal increment analysis, occurred from March to May for yellowtail snapper and from February through March for queen triggerfish.The maximum age for yellowtail snapper was 17 years, compared with only 7 years for queen triggerfish. Mean back-calculated fork lengths (FL, mm) of yellowtail snapper aged 1, 5, 10, 15 and 17 years were 117, 287, 375, 455 and 505, respectively. Mean back-calculated lengths for queen triggerfish aged 1–7 years were 161, 229, 274, 307, 332, 356 and 378 mm FL, respectively. The von Bertalanffy growth equations for yellowtail snapper and queen triggerfish were L_t=502.5 (1−e^{−0.139(t + 0.955)}) and L_t=415(1−e^{−0.30(t + 0.600)}) respectively, where t = age in years. The length-weight relationship for yellowtail snapper was W = 0.000117FL^2.6504, where W = weight in grams and was W = 0.000101FL^2.750 for queen triggerfish. Data revealed that yellowtail snapper live longer than previously reported and grow at a rate similar to other western Atlantic lutjanids. Queen triggerfish studied were not as old as expected, probably because of fishing gear selectivity.     

Research on intensive aquaculture: Proceedings of a German-Israeli seminar on aquaculture held from March 10 to 11, 1980 at Shefayim,Israel. H. Rosenthal and O.H. Oren (Editors). European Mariculture Society,Belgium, Special Publication No. 6, 1981. ii + 277 pp., BFr. 1150

A solar-heated greenhouse containing recirculating fish production systems was used to culture Tilapia nilotica and T. aurea. Fish production was maximized by sequential rearing, grading, and restocking of fish at high densities to utilize each system fully. Marketable-size (167 g) fish were produced from 29-g fingerlings in 137 days. No reproduction was recorded.Spawning in February was induced naturally by a $\text{16}\text{L}\text{8}\text{D}$ photoperiod, water temperature of 24°C, and reducing stock density.     

Heterozygosity in gynogenetic diploids and triploids estimated by gene-centromere recombination rates

We present methods for estimating the effect on heterozygosity of diploid gynogenesis and triploidy induced by suppressing the second meiotic division. The reduction in heterozygosity, as estimated by the fixation index (F), induced by a single generation of diploid gynogenesis is ($\text{1?}\text{y}$), where $\text{y}$ is the mean frequency of second meiotic division segregation. The fixation index in triploids at a single locus depends upon y and the number and frequencies of alleles present. A simple estimate of the maximum increase in heterozygosity is provided by $\text{F = ?(}\text{y}\text{2}\text{)}$; this estimate assumes that there are only two alleles at each locus. The minimum increase in heterozygosity at a locus with multiple alleles is $\text{F = ?(}\text{y}\text{n}\text{)}$, where n is the number of alleles present.     

Vulnerability of prey to predation by freshwater prawn,Macrobrachium malcolmsonii

The vulnerability of four prey species to predation by the freshwater prawn, Macrobrachium malcolmsonii, was found to be in order of decreasing vulnerability: tadpoles of frog (Rana cyanaphyctis) > minnow (Aplocheilus lineatus) > common carp fry (Cyprinus carpio) >Tilapia mossambica fry. The weight of the prey consumed per day was, respectively, 12.48 ± 1.45 g, 6.02 ± 1.15 g, 5.61 ± 0.40 and 2.89 ± 0.26 g; and the estimated 50% predation time was 1.25 ± 0.26 days, 1.66 ± 0.33 days, 2.0 ± 0.17 days, and 3.54 ± 0.72 days, respectively.     

Breeding-related growth of captive Sparus aurata (Teleostei,Perciformes)

Growth is arrested in male and female Sparus aurata during gonadal recrudescence and spawning. Growth and feeding rates of fish exposed to a constant long photoperiod ($\text{16L}\text{8D}$) were significantly higher than those of fish under a natural photoperiod. When the experimental photoperiod was shortened, fish underwent gonadal recrudescence and reduced feeding, and their growth was arrested. Fish under the long photoperiod regime reached the commercial weight of 350 g six months earlier than the controls.     

Growth of the green mussel, perna viridis L., in a sea water circulating system

Growth of the green mussel, P. viridis L., was studied in a sea water circulating system for 12 months. The maximum growth rate was recorded during March–May, coinciding with the maximum abundance of phytoplankton. The other hydrological parameters did not show any marked correlation with growth rate, which was chiefly influenced by the availability of food. A significant relationship was noted between the shell length and total weight of the mussel, i.e.

$\text{W = 3.7522 L}{}^{1.3007}$

The maximum growth rate (91.62%) was recorded at an early stage and was followed by a sharp decline to 5.78%. The growth pattern of the mussel fitted well with the von Bertalanffy growth equation:

$\text{Lt = 110 (1?e}{}^{\mathrm{?0.1124\; (t+0.0889)}}\text{)}$

     

The inhibition by ammonia of population growth of the rotifer, Brachionus rubens, in continuous culture

For the safe maintenance of microalgae and rotifers in mass culture, it is necessary to know the exact threshold concentration of ammonia for rotifers. In order to determine this threshold concentration, the continuous culture technique was used as a sensitive method to determine the influence of ammonia on the reproduction rate of the rotifer Brachionus rubens. As expected, only unionized (free) ammonia affected the population growth. Up to a concentration of 3 mg $\text{NH}{}_3\text{-N}\text{l}$ the reproduction of Brachionus was unaffected. In the range of 3–5 mg $\text{NH}{}_3\text{-N}\text{l}$ the reproduction rate decreased, although no animals were killed. This decrease was reversible and could be overcome by lowering the NH₃-N concentration. At concentrations over 5 mg $\text{NH}{}_3\text{-N}\text{l}$ the rotifers died within 2 days.     

A comparison of growth and survival of subtidal Crassostrea virginica (Gmelin) in South Carolina salt marsh impoundments

Four South Carolina salt marsh impoundments and their associated tidal creeks were assessed for the culture of subtidal Crassostrea virginica. The impoundments were chosen primarily for their diversity and ranged from old large impoundments with appreciable tidal exchange and surrounded by extensive low marsh, to new small impoundments with little tidal exchange and surrounded by maritime forest. Floating and bottom hardware cloth trays (1.22 × 0.61 × 0.14 m) each holding 200 seed oysters (initial length, $\text{y}\text{= 43.8}\text{mm}$) were placed at each location and sampled monthly for growth and survival. Coincidental monthly estimates of primary production (¹⁴C), phytoplankton concentrations and total organic carbon were performed. Ancillary data collected biweekly at all locations included standard hydrographic information (temperature, salinity, pH and turbidity) and nutrient determinations (nitrates, nitrites, orthophosphates and silicates).Results indicated that over a 6-month period (October–April) growth at all locations was significantly (α = 0.001) greater in ponds than in adjacent creeks and greater in floating than bottom trays. Growth means ranged from as little as 1.00 mm/month in the Wando River, to median values of approximately 2.25 mm/month in tidal creeks, to a relatively high growth rate of 3.11 mm/month in Blue Heron Pond (Kiawah Island). Survival was high in all areas ranging from 85.0% at Blue Heron Pond to 94.5% at Kiawah Creek. There was no significant difference in survival in comparisons among locations. A direct correlation of growth in oysters, primary production and phytoplankton biomass was established. This relationship was reiterated by indications of an inverse correlation between nutrient concentrations and growth.     

Preliminary studies on rearing of the gilthead seabream, Sparus aurata (L.), in brackish water ponds

The first attempt to rear the gilthead seabream, Sparus aurata, in brackish water ponds in Egypt was conducted from April 1976 to February 1977. Experimental ponds were stocked with Sparus aurata fry of about 32 mm and 1.5 g average length and weight respectively at a rate of 3000 fry per one feddan of pond water (i.e. 0.42 ha). The growth rate was recorded monthly. An average length and weight of 190 mm and 78 g respectively was attained after 8 months without supplementary feeding or fertilization of pond water. mathematical equations expressing length-weight relationship and condition factor were derived for both wild and reared fish. The higher values of condition factor obtained for the reared fish in comparison to the wild fish signify their improved condition and hence their suitability for farming in Egypt.     

Aquaculture development in less developed countries: Social,economic and political problems: Leah J. Smith and Susan Peterson. Bowker Publishing Company,Essex, U.K., 1982. 152 pp., US$ 29.50. ISBN 0-86531-235-4

Oxygen consumption and ammonia production in elvers of varying growth rates were studied. The allometric equation describing the relationship between oxygen consumption and weight is y =00.638 x^0,525, where y is the oxygen consumption (mg/h) and x is the mass (g). The weight specific allometric equation for the relationship between ammonia excretion and weight is $\text{y}\text{x}\text{= 0.0129 x}{}^{\mathrm{0,465}}$. Slow growing elvers were found to have higher respiratory rates (0.737 mg O₂ h^?1 g^?1) than would be expected for their size.     

Some aspects of the growth and yield of Gracilaria tikvahiae in culture

A series of outdoor, continuous-flow seawater cultures (50 l; 0.23 m²) were used to investigate the effects of culture density (kg/m²), nutrient loading (total nitrogen input/day) with both NH₄⁺N and NO₃^?N, and turnover rate ($\text{flow rate}\text{culture volume}$) on the growth and yield of Gracilaria tikvahiae. Although specific growth rates as high as 60% per day were recorded for Gracilaria at low densities (0.4 kg wet wt/m²) in summer conditions, maximum year-round yields were obtained at densities of 2.0–3.0 kg wet wt/m². Above a minimal daily nitrogen loading the yield of Gracilaria was independent of (1) nutrient concentration, (2) nitrogen loading, or (3) whether nitrogen was in the form of NH₄⁺N or NO₃^?N, but was (4) highly dependent upon flow rate. The time weighted mean annual production during 1976–1977 was 34.8 g dry wt/m²·day or 127 t/ha·yr based on 12-months continuous operation at near optimal densities and flow rates in the non-nutrient limited culture system.     

Growth response of Tilapia zillii fingerlings fed isocaloric diets with variable protein levels

Six purified casein diets within a range of 21–53% crude protein were fed for 3 weeks to young tilapia (Tilapia zillii) to determine the optimum protein requirement and protein: energy ratio for growth. Growth rate increased proportionally to protein level of the diet to an incorporation rate of about 35%. Beyond this a gradual retardation in growth rate was observed. The diet containing about 30% crude protein with a protein: energy ($\text{P}\text{E}$) ratio of 81, however, appeared to be more efficiently utilized by the fish in terms of protein deposition and energy retention than diets with higher levels of crude protein. These results indicate that Tilapia zillii requires about 35% protein in the diet for optimum growth while 30% for the maximum bodily protein deposition when casein is used as the sole source of protein. All six diets, however, showed an excellent feed conversion. Protein efficiency ratio (PER) decreased with the increase in protein in the diet.     

Rearing of coregonid fishes (Coregonidae) in illuminated lake cages: I. Growth and survival of Coregonus lavaretus L. and Coregonus peled Gmel.

The paper presents the results of rearing whitefish (Coregonus lavaretus L.) and peled (Coregonus peled Gmel.) in illuminated lake cages during a period of 4 years. In 3 successive years about 97 kg of summer coregonid fry were produced during initial 2-month rearing. Whitefish fry reached a length of 30.0–49.5 mm and an average individual weight of 201 mg–1 g. Peled fry reached 31.0–38.3 mm in length and 300–370 mg in weight. Whitefish survival rates amounted successively to 72.6% in 1977, 51.4% in 1978, and 3.1% in 1979. Survival rates for peled were 57.8%, 63.1% and 6%, respectively. Fishes at the age of 1+ and 2+ years showed high mortalities. Their growth rate was slower than in wild populations, and they did not attain sexual maturity.     

Dependence of Coregonus albula embryogenesis rate on the incubation temperature

Eggs stripped from Coregonus albula were incubated at different constant temperatures. The duration of embryogenesis varied from 183 days at 1.1°C to 45 days at 9.9°C. We describe the course of embryogenesis using 16 easily recognizable developmental stages (DS j). Development rate (DR j) for any given stage (DS j) is expressed as the reciprocal of time (in days) from fertilization to attainment of a given developmental stage. The generalized equation relating rate of development to stages DS j with respect to temperature (x) is

The values of DR to the “eyed egg” stage and to 50% hatch, expressed as percentage per day of the total development period, were computed and tabulated for temperatures ranging from 0.1 to 9.9°C. To verify the derived regression model we observed the course of embryogenesis of C. albula eggs incubated in a commercial hatchery at fluctuating temperatures. The observed times of attainment of the successive developmental stages were compared to the predicted times based on mean daily water temperatures. The time observed agreed well with times predicted by the model; the only exception was the time of hatching, which was systematically overestimated (5 to 7 days) by the model. This was possibly due to the influence of dissolved oxygen on the time course of hatching processes, which was not considered in our regression model.     

The length-weight relationship,food habits and condition factor of wild juvenile milkfish in Sri Lanka

Wild juvenile milkfish (Chanos chanos) were obtained from Negombo lagoon in September 1984. Thirty-one specimens (92–186 mm FL) had a fork length-body weight relationship of log W = −5.6083 + 3.2598 log L. These fish were caught in the early morning and had empty guts. The mean condition factor (K) was 8.7. The intestine length to fork length ratio (I) was 3.7. Two large specimens (245 mm and 340 mm FL) caught around mid-day from the ocean off Negombo had full guts. Food was mostly blue-green algae, diatoms and detritus, with a number of copepods and nematodes. These fish had K values of 11.7 and 13.6 and I values of 8.1 and 8.5. The age and the month of spawning of these fish were back-calculated using known milkfish growth rates. It seems that in Sri Lanka, milkfish spawn from January to at least November.