Effects of light administration and algae on first feeding of Atlantic halibut larvae, Hippoglossus hippoglossus (L.)

The aim of the study was to investigate the effects of two light regimes that independently had shown positive effects on feeding and growth in cultures of Atlantic halibut, Hippoglossus hippoglossus (L.), larvae. The regimes were low-intensity overhead light and submerged light at intermediate light intensities. Secondly, an alleged beneficial effect of algae was investigated. An experiment was designed to include four different regimes in the larval cultures: low-intensity overhead light with and without algae (Tetraselmis sp.), and submerged light with and without algae. The results showed that submerged light was superior to overhead light with respect to larval growth, survival and feeding incidence. It was further indicated that algae improved larval growth and survival, but no effect was shown on feeding incidence. There was, however, no interaction between the effects of algae and those of the light regime. The causal effect of the algae may be ascribed to indirect factors, such as light attenuation as well as a direct and indirect nutritional effect.     

3D conservation planning: Including aquifer protection in freshwater plans refines priorities without much additional effort

1. Groundwater has very rarely been included in modern systematic conservation planning methods that identify key areas for protection of aquatic organisms.
2. Three conservation plans were developed for aquatic ecosystems in the Hunter Valley, NSW, Australia using the planning software Marxan: one model for rivers and wetlands and two that consider groundwater ecosystems. The first of these groundwater inclusive models included aquifers in the initial planning process; the second retrofitted groundwater onto an existing conservation plan.
3. The results demonstrate that, if groundwater protection was included at the planning stage, the overall land that was needed only increased marginally. When included, groundwater protection led to an emphasis on groundwater recharge zones. A posteriori inclusion of GW protections, however, yielded a 30% increase in surface area needing protection.
4. We conclude that groundwater can be included in conservation planning but it is much more efficient to do so at the beginning of the planning process.
5. The next step is to refine the planning methods by including data on groundwater‐dependent organisms, either by genetic means or novel statistical techniques, and hence using a direct biotic signal instead of environmental surrogates.

     

THE EFFECT OF FISH MEAL CONTAINING DIFFERENT LEVELS OF FISH SOLUBLES ON THE GROWTH OF RAINBOW TROUT (Salmo gairdneri)

Two experiments were conducted to examine the effect of fish soluble additives in fish meal used as a protein source in dry diets to rainbow trout. Experiment I was made up by 3 dietary groups, run with 4 replicates of 100 trout on each diet. The protein sources examined were as follows: (1) presscakemeal, (2) whole meal, and (3) whole meal + lysine to the same levels as (1). The experiment was run for 12 weeks with ad libitum feeding three times a day. The results showed significantly lower (P < 0.05) weight gain for trout given presscakemeal as compared with whole meal. Experiment II evaluated 3 diets, run in triplicates with 100 trout in each aquarium. Presscakemeal (1), whole meal (2), and whole meal + extra addition of fish solubles (3) were examined as protein sources. The experiment was conducted for 16 weeks. The average weight gains were not significantly different among the dietary groups. The conclusion drawn from the experiments is that fish meal with fish soluble additives is preferred as a protein source in feed for rainbow trout.     

An Intensive Approach to Atlantic Halibut Fry Production

The larval stage is regarded to be the main bottleneck of halibut production. Halibut eggs were obtained from captive broodstock both by stripping and by natural spawning. Artificial photoperiods were used to increase the total spawning season. Yolk sac larvae are presently produced either in small stagnant units or in large flow through systems. A major consideration is to avoid stress of the larvae, caused by mechanical disturbances of the larvae and by high bacterial load or high ammonia levels in the water.
The experiments showed that halibut larvae began to ingest algae earlier than rotifers Brachionus sp. Supplementation of algae to first feeding tanks resulted in enhanced survival and growth rate of the larvae. Both rotifers and Artemia can be enriched with very high levels of highly unsaturated n-3 fatty acids (n-3 HUFA). Enriched live feed, containing high levels of n-3 HUFA and total lipids, enhanced both survival and growth of the halibut larvae. The highest growth rates were obtained with wild zooplankton and addition of algae, but enriched cultivated feed combined with algae resulted in growth of the same magnitude as with wild zooplankton.     

Glauconite from the Precambrian Belt Series, Montana

Glauconite from the upper part of the Missoula Group of the Belt Series, Flathead County, Montana, has been dated at 1070 million years by potassium-argon and rubidium-strontium analyses. This is the first glauconite of Precambrian age reported in North America.