Aquaculturists typically report growth using absolute (g/d), relative (% increase in body weight), and specific growth rates (%d). Less frequently, von Bertalanffy Growth Functions (VBGF) are used. Each of these rates is a numerical representation of growth which assumes a specific relationship between size and time (linear, exponential, or asymptotic). Aquaculturists typically determine size at time throughout their experiments. Unfortunately, the intermediate data points are usually ignored when computing growth rates (except for VBGF) and the appropriateness of the method for calculating growth for a particular data set is not tested. This paper reviews the basis and computation of each of the growth rates in an effort to encourage aquaculturists to use the appropriate growth rates.

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Phosphorous removal 1,000,000 tons Assumes phosphorous content 0.2% of dry weight. Represents 61% of the phosphorous input as fertilizer. Carbon assimilation 135,000,000 tons Assumes carbon content 27% of dry weight. Equals 6% of the carbon added annually to oceans from greenhouse gas emissions. Bioenergy potential 1,250,000,000 MWH Assumes 50% carbohydrate content, converted to energy. Equals 1% of annual global energy use. Land sparing 1,000,000 km 2 Assumes 5 tons/ha average farm yield. Equals 6% of global cropland. Freshwater sparing 500 km 3 Assumes agricultural use averages 1 m 3 water/kg biomass. Equals 14% of annual global freshwater withdrawals.

This study investigated endocrine control of branchial ionoregulatory function in Nile tilapia (Oreochromis niloticus) by prolactin (Prl188 and Prl177), growth hormone (Gh) and cortisol. Branchial expression of Na(+)/Cl(-) cotransporter (ncc) and Na(+)/K(+)/2Cl(-) cotransporter (nkcc) genes were employed as specific markers for freshwater- and seawater-type ionocytes, respectively. We further investigated whether Prl, Gh and cortisol direct expression of two Na(+), K(+)-ATPase (nka)-α1 subunit genes, denoted nka-α1a and nka-α1b. Tilapia transferred to fresh water following hypophysectomy failed to adequately activate gill ncc expression; ncc expression was subsequently restored by Prl replacement. Prl188 and Prl177 stimulated ncc expression in cultured gill filaments in a concentration-related manner, suggesting that ncc is regulated by Prl in a gill-autonomous fashion. Tilapia transferred to brackish water (23 ‰) following hypophysectomy exhibited a reduced capacity to up-regulate nka-α1b expression. However, Gh and cortisol failed to affect nka-α1b expression in vivo. Similarly, we found no clear effects of Gh or cortisol on nkcc expression both in vivo and in vitro. When considered with patterns previously described in euryhaline Mozambique tilapia (O. mossambicus), the current study suggests that ncc is a conserved target of Prl in tilapiine cichlids. In addition, we revealed contrasting dependencies upon the pituitary to direct nka-α1b expression in hyperosmotic environments between Nile and Mozambique tilapia.

Abstract. Three experiments were conducted to evaluate the potential for culturing tilapia in tanks and raceways with flowing sea water (39‐41 ppt salinity) in Kuwait. In the first and third experiments, fingerling tilapia were grown for 7 to 8 months under ambient conditions. In the second experiment, larger (50‐100g initial weight) male tilapia were grown for 6 months. Growth and mortality rates were determined. Oreochromis aureus (Steindachner) grew the slowest and survived poorly. O. spilurus (Günther) and O. aureus × O. spilurus hybrids had the best survival and moderate growth rates. A red tilapia from Taiwan grew the fastest but had high mortality rates during winter. O. spilurus and the hybrid were best suited for seawater culture under ambient conditions in Kuwait.

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During three S-month experiments in Thailand, earthen ponds of approximately 370m^ surface area were stocked with male Nile tilapia, Oreochromis niloticus (L.), fingerlings of 4~12g weight at densities of 0-5 to l-6fish/m^. Slocking and fertilization (with chicken manure, urea and TSP) in triplicated depth treatments of 0-6,10 and 1-5 m were proportional to pond volume in two experiments (wet and dry seasons) and to pond area in the other (dry season).Depth showed no direct effect on fish yields of 0-9-6-3t/ha/year. on survival rates of 66 to 98%, nor on final individual weights of 96-313 g/fish. Greater yields were obtained from deeper ponds when they received proportionally greater stocking and fertilizer inputs. Inputs per unit area were the most important factor accounting for yield variation.Temperature, dissolved N and P, and suspended solids showed little or no relation to depth treatments. Time-averaged chlorophyll concentrations and photosynthetic production of dissolved oxygen were greater in treatments receiving greater inputs of nitrogen per unit pond volume.Deeper ponds produced the greatest areal yields of fish, when fertilized in proportion to their volumes. Shallow ponds produced fish and dissolved oxygen at least as efficiently per unit input as did deep ponds, which is consistent with models of photosynthesis-depth relations.

SUMMARYThroughout the tropics, developing countries and territories are highly dependent on nearshore marine resources for food and income, however information on the sustainability and proper management of these fisheries is lacking. In Pohnpei, Micronesia, the sustainability of a coral reef finfishery was assessed by comparing coral reef fish demand to coral reef biocapacity using a marine ecological footprint (MEF) analysis. Based on geo-referenced satellite and aerial imagery, Pohnpei and surrounding atolls have 184.2 km2 of coral reef habitat with a sustainable finfish yield of 573–1118 t yr−1, however total harvest was estimated at 4068 t yr−1, exceeding biocapacity by 360–710%. The MEF was supported by observed impacts to coral reef resources, including (1) long-term declines in fish spawning aggregation density, (2) reductions in mean size, age and fecundity of key commercial species, (3) reliance on undersized fish, and (4) decadal declines in mean size and abundance of fishes of iconic value and critical to ecosystem maintenance. The commercial fishery was responsible for 68% of finfish catch volume, while reef fish consumption, at 93 kg person−1 yr−1, was among the highest in the region. To sustainably meet current demand, up to 833 km2 of additional reef area would be required. The study illustrates the MEF, at least rudimentarily, reflects biological reality on local reefs and represents a valuable analytical tool in a marine policymaker's toolbox.